PRACTICAL NUTRITIVE REQUIREMENTS OF POULTRY

PRACTICAL NUTRITIVE REQUIREMENTS

OF POULTRY

by Harry W. Titus ^

THIS article discusses the results of some of the many studies on which modern poultry-feeding practices are based. It might be called the theory

of poultry feeding, since it is concerned with the needs of the birds for the

various nutritive elements in relation to reproduction, egg production,

growth, and fattening. In another article, Practical Feeding of Poultry,

these needs are translated into terms of actual feedstuffs.

BECAUSE of the greater economic importance of chickens, their nutritive requirements have been studied more extensively than have those of turkeys, guineas, pigeons, ducks, and geese. As a result of these studies, much dependable information about the quantitative nutritive requirements of chickens for growth, egg production, and hatchability has been obtained. (Figure 1 shows the interior of a modern laboratory in which chemical analyses are made for the control of poultry-nutrition experiments.) During the last 6 or 7 years, nutrition experiments conducted with turkeys have greatly increased in number and have added materially to our knowledge of the nutritive requirements of this species. Relatively little is known about the quantitative nutritive requirements of guineas, pigeons, ducks, and geese.

Qualitatively the nutritive requirements of chickens are in many ways the same as those of other animals, but quantitatively they are appreciably different. In other words, most animals require proteins, fats, carbohydrates, vitamins, and minerals for normal growth and reproduction, but they do not require the same relative quantities of these nutrients. Another difference is that the feed of chickens consists mostly of concentrates, whereas that of cattle, horses, sheep, and goats includes a rather large portion of roughages. In this respect chickens are more like swine than they are like any of the other domestic animals.

Ordinarily chickens are kept primarily for the production of meat and eggs, and for this reason they are seldom rationed; that is to say,

1 Harry W. Titus is Senior Biological Chemist, in charge of Poultry Nutrition Investigations, Bureau of Animal Industry.

787

> 00 o o O -n

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I I fin re ¡.—interior of a modern laboratory, in wliielí ehenncal analyseH are made tor llie eonlrol of |«()iillr\-niilrilion experiments.

REQUIREMENTS OF POULTRY 789

instead of some suitable but fixed quantity of feed each day, they are usually fed all they can be induced to eat. Such full feeding is desirable because rapid growth is generally necessary for the economical production of meat, even though full-fed chickens utilize their feed somewhat less efficiently for growth than do chickens that consume appreciably less feed. Moreover, high egg production cannot be maintained if the feed supply is limited. For these reasons special care must be taken to balance the diets of chickens so that the economical production of flesh and eggs will be the ultimate result.

If considerably more protein, fat, and vitamins are supplied than are required, the chickens may be well but not economically nourished, because these three nutrients are usually the most expensive. It is not economical to force chickens to use protein and fat as sources of energy when the cheaper carbohydrates will serve the same purpose just as well, or even better; or to feed vitamins in gross excess of requirements; or, on the other hand, to supply too small quantities of minerals and vitamins and thus cause the chickens to use the protein in their diet less efficiently. It is more economical, however, to feed somewhat more protein and vitamins than may be required than it is to feed too little. This is also true of the mineral elements; but in attempting to supply adequate quantities of these there is likely to be a tendency to use too much because they are relatively cheap. Any great excess of minerals in the diet should be carefully avoided because in some cases such excess may be definitely harmful.

The nutritive requirements of chickens have been studied from several standpoints. What are the special requirements for high hatchability of the eggs that are to produce a new generation? What are the special requirements for high egg production, irrespective of hatchability? Are there special requirements for the growth of young stock? Finally, what are the requirements for fatteDing? At the risk of some repetition, this article will discuss nutrititive requirements in the order given in these four questions, bringing out differences in nutritive needs for each function. There will be a brief discussion of the nutrituve requirements of turkeys, and at the end, a table sum- marizing the available information for both chickens and turkeys.

EFFECT OF NUTRITION ON REPRODUCTION IN THE CHICKEN

Reproduction in the chicken is different in several ways from reproduction in the other farm animals. It is much more rapid, the embryo develops outside the body, and the food of the young is not prepared within the body of the mother. In the other farm animals the development of the embryo from its inception to its birth is influenced by the contemporary feed supply of the mother. In the chicken, as in all poultry, the feed supply of the developing embryo is fixed within a relatively short time after the egg is fertilized, and thereafter until hatching the development of the embryo is independent of the contemporary feed supply of the mother. Once a fertile egg is laid, the nutritional fate of the contained embryo is fixed, except insofar as it may be influenced by the egg's physical environment. Neverthe-

790 YEARBOOK OF AGRICULTURE, 1939

less, diet may affect reproduction just as markedly in chickens and other poultry as in cattle, sheep, and swine.

Three ways in which diet may affect reproduction in the chicken may be considered. (1) It may affect the quantit}^ and fertilizing- capacity of the sperm produced by the males and thereby affect the number of eggs fertilized; (2) it may affect the egg production of the females; and (3) it may affect the composition of the eggs and thus, in turn, the hatchability of those that are fertile.

DIET OF THE MALES

There is very little definite information about the effect of the diet of male chickens on their ability to produce sperm or on the fertilizing capacity of their sperm. Because a deficiency of vitamms A and E, either one or both, eventually leads to a failure of sperm production in the rat, it has been assumed that the same is probably true in other species. However, the writer has kept adult male chickens for more than 6 months on a diet that contained only about 10 International Units of vitamin A per 100 grams of feed—that is, about 6 to 10 percent of the minimum requirement of actively growing chicks—without observing any decrease in their sperm production. Similar results were obtained when a diet rendered deficient in vitamin E by treatment with a solution of ferric chloride in ether was fed for 5 months. Furthermore, Adamstone and Card (15) ^ found that male chickens could be kept on a diet deficient in vitamin E for at least a 3êar, and in. some cases for as long as 2 years, without losing their ability to fertilize. Thus it may be concluded that, although male chickens may eventually become sterile if kept on diets that are markedly deficient in either vitamin A or E or in both, they are able to subsist for a rather long time on such diets without losing their ability to fertilize.

It has been claimed that when male chickens are fed a diet in which the protein is derived from plant sources only they mate less frequently than when their diet contains some animal protein. Also, it has been reported that in one experiment the feeding of silage to male chickens tended to increase their sperm production. In both cases the experimental technique appears to have been faulty and incapable of yielding results from which reliable conclusions " could be drawn.

The available experimental evidence indicates that it is difficult to decrease the sperm production or the fertihzing capacity of adult male chickens by dietary means, unless a given deficient diet is fed for a rather long time or unless the dietary deficiency is such that it affects the general health of the males. Also, there is no acceptable experimental evidence that the sperm production or fertilizing capacity of healthy male chickens can be increased by diet.

DIET AND HATCHABILITY

There is an abundance of evidence that egg production in the chicken is affected by diet. This phase of the subject is discussed in a section of this article which deals specifically with egg production (p. 799).

Some of the earliest observations regarding the hatchability of chicken eggs were: (1) That eggs laid during the winter did not hatch so well as those laid during the spring or summer; (2) that fewer eggs

2 Italic numbers in parentheses refer to Literature Cited, p. 1075,


hatched if the chickens were confined than if they had access to sunshine and range; and (3) that the feeding of green feedstuffs generally improved hatchability. Research in poultry nutrition has supplied the explanation for these observations. Eggs produced during the winter did not hatch well chiefly because the chickens did not get enough vitamin D. For the same reason, fewer eggs hatched when the chickens were confined. Green foodstuffs tended to improve hatchability because they supply vitamin A and riboflavin (vitamin G), and other important nutritional factors as well. The discovery that cod-liver oil is an excellent source of vitamin D and that certain feedstuffs, such as alfalfa-leaf meal, are good sources of vitamin A and riboflavin has made it possible to improve greatly the hatchability of eggs laid during the winter or by chickens kept in confinement, even though no fresh green feed is supplied.

If the diet fed to chickens affects the composition of their eggs, it is logical to assume that it may also influence the development of the embryo and thus be an important factor in determining whether or not the eggs will hatch. There is ample evidence that diet may affect both the composition of eggs and their hatchability, and some of this evidence will now be presented and discussed.

Effect of Diet on the Composition of ttie Egg and tlie Embryo The writer and his associates {II4O) have obtained data that indi-

cate that diet has at least a slight effect on the composition of both the yolk and the white of eggs and that the composition of the former is more readily changed than that of the latter. The percentage of protein and fat in the dry matter of the yolk is most readily affected, but the magnitude of the effect is small. McFarlane, Fulmer, and Jukes (728) determined the quantity of the three amino acids, tyrosine, tryptophane, and cystine,^ in both the white and the yolk of eggs produced by hens that had received different diets and found no significant differences attributable to diet. Calvery and Titus (187) made somewhat more complete analyses of the white and yolk, and of the albumins and the vitellins,^ of eggs laid by pullets that had been raised and kept on three diets which differed only in the source of the protein. The three sources of protein were (1) wheat middlings, (2) corn and corn-gluten meal, and (3) soybean meal. They observed no marked differences in the composition of the proteins of the eggs. Thus, according to the experimental evidence just cited, diet may affect the percentage of protein in both the yolk and the white but not the composition of the constituent proteins.

It has been demonstrated that both the percentage of fat in the yolk (1140) and the composition of the fat (24^) may be influenced by diet. This was to be expected because the transference of fat from the feed to the maturing yolk may take place within 2 or 3 hours after the feed is ingested. According to Cruickshank^s experiments (242), the chicken utilizes ingested fats for direct deposition in the egg even when abundant carbohydrate is present for the synthesis of normal fat; however, if there is a deficiency of carbohydrate a greater proportion of the ingested fat will be deposited in the egg. This same inves-

3 See the article on Protein Requirements of Man (p. 173) for descriptions of the amino acids and their functions.

* The albumins and the vitellins are, respectively, the chief proteins of the white and of the yolk.


tigator concluded from her studies that although the degree of satura- tion and the proportion of the component fat acids in the egg could be considerably modified by the ingestion of unsaturated fat acids in the feed, the ingestion of saturated fat acids had relatively little effect in altering the normal composition of the mixed fat acids in the yolk.

Several groups of investigators have demonstrated that the vitamin content of eggs may be influenced by diet. The quantity of vitamin A and of vitamin D may be made to vary over a rather wide range by varying the quantity in the diet. As was shown by Hart and associates (492) the vitamin D content of the eggs of chickens confined without access to sunshine may be increased as much as ten- fold by subjecting the chickens to ultraviolet radiation. According to Kussell and Taylor (997) the output of vitamin A in eggs may be as much as 32 percent of the quantity consumed in the feed, whereas only about 10 percent of the vitamin D in the feed is found in the eggs. However, De Vaney, Munsell, and Titus (274-) were able to obtain a transfer of only a little more than 2 percent of the vitamin D from the feed to the eggs. There are few quantitative data on the relation between the output of the other vitamins in eggs and the quantity consumed; nevertheless it has been demonstrated that under experimental conditions the quantity of vitamins Bj and E and of riboflavin in eggs may be influenced by diet.

Likewise, it has been shown that the mineral content of eggs and of the developing embryos may be affected by diet and, in some cases, b}^ irradiation with ultraviolet rays. Buckner and Martin (Î65) observed that a limitation of the calcium in the diet of chickens caused thin shells to be formed but did not markedly affect the calcium content of the liquid portion of the egg. Buckner, Martin, and Peter (167) determined the calcium and phosphorus content of strong and weak chicks from hens of which some had received calcium carbonate in their diet and others had not. They found that both the quantity and percentage of phosphorus were approximately the same in strong as in weak chicks but that both the quantity and percentage of calcium were less in the weak than in the strong chicks. Insko and Lyons (576) were able to demonstrate that both the calcium and the phosphorus content of the embryos were less when no vitamin D was supplied than when the chickens received an adequate supply. Erik- son and CO workers (333) obtained evidence that either cod-liver oil or sunshine tended to increase the inorganic phosphorus content of the egg yolk. And Hart and associates (492) found that the embryos in eggs from hens which had been irradiated with ultraviolet rays contained about twice as much calcium after 21 days of incubation as did the embryos in eggs from hens which had not been irradiated.

The quantity of some of the other mineral elements in eggs may also be affected by diet. Lyons and Insko (705) showed that the manganese content of the feed markedly affected the manganese content of the eggs. Erikson and coworkers (332) found that the addition of 2 percent of cod-liver oil to the basal diet of their hens raised the percentage of both copper and iron in the yolk of the eggs, and that sunshine, but not filtered sunlight,^ had a similar effect. Strangely

* Sunlight from which the ultraviolet portion has been excluded by filtering, as through ordinary window glass.


enough, however, the combination of sunshine and cod-liver oil did not increase the iron content as much as did the cod-hver oil alone, but it caused a greater increase in the copper content. It has been reported that merely adding iron compounds to the diet of cliickens has no demonstrable effect on the iron content of the eggs, but it has been claimed that the feeding of plant materials rich in iron tends to increase the iron content.

Several investigators have shown that the iodine content of eggs can be readily increased by increasing the iodine content of the diet. That the iodine content of eggs is ordinarily quite low may be inferred from the observation, of Wilder, Bethke, and Record Í1220) that the daily feeding per bird of only 2 and 5 milligrams of iodine in dried kelp, iodized linseed meal, or potassium iodide increased the iodine content of the eggs approximately 75 and 150 times, respectively.

While studying fluorine toxicosis (a disease condition due to fluorine poisoning) in laying hens, Phillips, Halpin, and Hart {920) obtained evidence that a part of the fluorine in the feed is transferred to the yolk of the eggs and that probably it is deposited in combination with the complex lipoids ^ of the yolks. Evidence that the highly toxic element, selenium, may also be transferred from, the feed to the egg has been obtained by Poley, Moxon, and Franke {929).

Many other substances may be transferred from the feed to the ç^gg, some of which are benzoic acid, certain fat-soluble dyes, and several of the plant pigments, such as xanthophyll, zeaxanthin, cr^^pto- xanthin, and capsanthin.

Relation of Protein to Hatchability Some of the earliest studies of the effect of dietary protein on.

hatchability were made by Parkhurst {895) who coTîchided tliat to obtain maximum hatchability, the diet should contain sufficient animal protein and vitamins. In later studies made by Byerl}^, Titus, and Ellis {178) no correlation was found between hatchability and the percentage of protein in the diet, but it was observed that certain protein supplements were significantly better than others in their effect on hatchability. The experiments of these workers clearly indicated that the second-week embryonic mortality was greater wlien the chickens were fed diets containing plant-protein supplements than when they were fed diets containing animal-protein supplements. They found that a large number of chondrodystrophic ^ embryos were obtained when the former diets were fed and concluded that some of the protein supplements which they had studied were deficient either in some vitamin or in the quality of the protein itself. They also found that the chondrodystrophy was eliminated when the chickens were permitted to have access to range. This latter findirig explains in part the apparently contradictory observation made in earlier studies by Parkhurst and Rhys {896) that the kind of protein supplement had little effect on hatchability, because in the experiments of these workers the chickens had access to grass runs. In this connection it may also be stated that Parkhurst and Rhys observed that

6 Lipoids are fats or fatlike compounds containing nitrogen. ■^ Exhibiting an abnormal condition of the bones, presumably due to a defective or faulty nutrition of the

cartilage of the bone. In this case the chondrodystrophy was characterized by a shoitening of the leg bones and the development of a parrotlike beak.


hatcliability was better when mixed protein supplements were used than when the sole protein supplement was meat-and-bone meal.

Further evidence that proteins from different sources may affect hatchability differently has been obtained by Titus and associates (ÎI4I), who found that when liquid stick (the concentrated liquor from the steam rendering of fatty animal material) was used as a protein supplement, the egg production was almost as good as when a high- grade meat scrap was used, but the hatchability of the eggs was very much poorer. A mixture of blood meal and stick had an even more pronounced and deleterious effect on hatchability than did stick alone. With both supplements embryonic mortality increased throughout the incubation period, but the increase was most pronounced during the last 11 or 12 days. Smith and Branion {1075) found that a mixture of liver meal and dried buttermilk affected hatchability more advanta- geously than did either one alone and suggested that this combination of protein supplements supplies the same essentials as does good grass range.

In considering the effect on hatchability of the protein in the diet, it is of some significance that neither McFarlane, Fulmer, and Jukes {728) nor Calvery and Titus {187) were able to demonstrate that the source of the dietary protein has any appreciable effect on the composition of the proteins of either the white or the yolk of the resulting eggs. However, the observations of Patton {898)^ that when embryonic mortality is associated with chondrodystrophy the embryos contain less than the normal quantity of glycine (one of the amino acids), indicate that hatchability may be influenced by the protein in the diet or by factors which affect protein metabolism. It has been suggested that the difference between plant-protein and animal- protein supplements in their effect on hatchability is due to the fact that the latter contain one or more vitamins not present in the former. It is known that animal-protein supplements are, as a class, better sources of riboflavin (vitamin G) than are plant-protein supplements. However, in the study of packing-house byproducts made by Titus and associates {II4I), the stick and high-grade meat scrap they used had very nearly the same riboflavin content, but the hatchability was very much lower on the diets that contained the stick than on those that contained the high-grade meat scrap.

The effect of the quantity of protein in the diet on the hatchability of the eggs produced has received relatively little attention. Heiman, Carver, and St, John {501) concluded that the diet of laying hens should contain about 15 percent of protein, but in their experiments the best hatchability was obtained when the diets contained about 16 percent. The writer found that if the protein content of the diet is reduced sufficiently, the hatchability is decreased, and concluded from his experiments that for both good egg production and hatchability the diet should contain about 16 percent of protein of good quality.

Fat and Carbohydrate in Relation to Hatcliability The effect on hatchability of the kind or quantity of fat and carbo-

hydrate in the diet appears not to have been studied. However, in view of the fact that Titus, Byerly, and Ellis {II4O) and Cruickshank {242) found, respectively, that the percentage of fat in the yolk and the


composition of the fat may be influenced by diet, tlie study of the eíFect of dietary fat on hatch ability should yield some valuable results.

Vitamins and Hatchability

Vitamin A It is generally agreed that vitamin A is required for good hatcha-

bility, but there is conflictiug evidence about the quantity required. Tliis state of affairs is due in part to the fact that different investigators have used different breeds of chickens and have measured the requirement in diflerent units, and that there is some disagreement about the factors that should be used in converting from one system of units bo another. The writer interprets the data of Russell and associates (996) as indicating that at least 840 International Units of vitamin A per 100 grams (about 3.5 ounces) of feed are required for the heavy production of eggs of high vitamin content, especially if good hatchability is to be maintained. According to Bearse and Miller (73) a diet supplies enough vitamin A for breeding stocl^ if it contahis about 700 International Units per 100 grams. However, it may be concluded from the studies of Sherwood and Fraps (1057) that tlie diet should supply about 1,050 International Units per 100 grams of feed for the maintenance of health and the production of eggs of high vitamin A content. Unfortunately, most of the experimental work has been done for the purpose of determining the minimum rather than the optimum requirement of vitamin A for good hatchability, and in practical poultry husbandry the optimum requirement rather than the minimum requirement should be supplied. According to the writer's experience, the optimum level of vitamin A intake is about 1,040 In- ternational Units per 100 grams, or about 4,720 International Units per pound, of feed, and this value is in good agreement with that deduced from the work of Sherwood and Fraps (1057).

Vitamin Bt

Payne and Hughes (899) concluded that a deficiency of vitamin Bi will reduce hatchability; but their vitamin B-deficient diets were also deficient in riboflavin (vitamin G), and so their conclusion cannot be accepted. Ellis and associates (382) also used a diet that was deficient in vitamin Bi and riboflavin, and they foimd tliat only about 15 percent of the resulting eggs hatched and that the hatchability was not greatly improved by adding good sources of vitamin Bi (rice bran and rice middlings) to the diet. Chicks hatched from the eggs produced on this deficient diet showed symptoms of polyneuritis soon after hatching, but failed to show the symptoms when rice byproducts were added. In view of the fact that some of the eggs hatched on a diet so deficient in vitamin Bi that there was a high incidence of polyneuritis among the hens to which it was fed, it must be concluded tentatively that the essentiality of vitamin Bi fqr hatchability is doubtful, or that only an exceedingly small quantity of this vitamin is required.

Vitamin C

There is good evidence that the chicken is able to synthesize vitamin C, and hence it may be assumed that it requires this vitamin for the


performance of its normal body functions. It has been demonstrated by several workers, however, that the chicken does not require pre- formed vitamin C in its diet.

Vitamin D

Hughes, Payne, and Latshaw (So9) were among the first to show that vitamin D is necessary for the production of hatchable eggs. Carver and associates (i^5) have reported that although 67 International Units of vitamin D ^ per 100 grams of feed are sufficient for good egg production, 135 units per 100 grams of feed are required for good hatchability. Bethke and associates (98) found that only 54 International Units of vitamin D per 100 grams were enough for good hatchability. Mur- phy, Hunter, and Knandel (830) reported that Single Comb White Leghorn pullets, which had been confined without access to sunshine but which had received 78 International Units per 100 grams of feed from the time of hatching, gave satisfactory results from the standpoint of both egg production and hatchability. From unpublished observations, the writer concludes that the optimum level of vitamin D intake for heavy egg production is about 120 International Units per 100 grams or about 540 per pound of feed, and that if there is enough vitamin D in the diet to support heavy egg production there is enough for good hatchability.

The possibility of supplying too much vitamin D is demonstrated by the researches of Branion and Smith (148) and of Titus and Nestler (1144)' The first two workers found that an excess of vitamin D from viosterol (a solution of irradiated ergosterol in oil) markedly decreased hatchability. The second two workers confirmed this finding and demonstrated that an excess of vitamin D from cod-liver oil has the same effect.

Vitamin E

That vitamin E is essential for hatchability was first demonstrated by Card, Mitchell, and Hamilton (190) in 1930. Five years later Bar- num (62) concluded from his studies that vitamin E deficiency in the chicken is manifested by an increase in the first-week embryonic mortality. There are no reliable data on the quantitative vitamin E requirement for good hatchability. The available evidence on the subject indicates, however, that the ordinary poultry diets contain enough vitamin E to support good hatchability.

RihoHavin (Vitamin G)

Halpin, Holmes, and Hart (1242) observed that hens may lay the normal number of fertile eggs and appear to be healthy even though their diet is deficient in vitamin G, but that as a result of the deficiency many of their eggs fail to hatch. Bethke, Record, and Wilder (99) concluded that embryonic development of the chick is dependent on the vitamin G (complex) content of the egg. The quantitative vita-

8 The standard unit for the measurement of vitamin D potency is the International Unit. Assays of thé potency of sources of vitamin D are made, according to the deflnition of the International Unit, with rats; but chickens do not react to all sources of vitamin D in the same way as do rats. Accordingly, the Associa- tion of OiBcial Agricultural Chemists has devised a method of assay in which chicks 1 or 2 days old are used as the test animals. When the source of vitamin D being assayed is pure cod-liver oil, 1 A. O. A. O. chick unit is equal to I International Unit, but when other sources are being assayed, 1 A. O. A. O. chick unit may be equal to as many as 100 International Units. The potency of cod-liver oil or other sources of vitamin D that are to be used in the feeding of chickens should be stated in terms of A. 0. A. C. chick units.


min G requirement for good hatchability has been determined recently by Davis, Norris, and Heuser (^68). These workers concluded that about 245 micrograms ^ per 100 grams, or about 1,110 per pound, of feed are required; and this value is in good agreement with the earlier estimate of 230 micrograms per 100 grams of feed made by Norris and associates (863),

Unidentified Factors

When a diet already adequate in vitamins A, D, E, and G, which are known to affect hatchability, is supplemented by certain animal proteins or by green grass, the hatchability of the eggs is significantly improved. This was established by Nest]er and associates {84-6) and by Hunt, Record, and Betlike {562). Their work indicates that some unidentified factor in these feeds brings about the improvement. The unidentified factor is lacking in dried whey, since hatchability was not improved when this was used as the supplement.

Effects of Minerals on Hatchability

Calcium and Phosphorus

The importance of an adequate dietary supply of calcium for good hatchability was demonstrated by Buckner, Martin, and Peter {166^ 168). These workers concluded that the addition of calcium carbonate to the diet of chickens is essential for the maintenance of the hatchability of their eggs. That too much calcium may adversely affect hatchability was shown by Titus and associates (1142). These workers also found that the effect of an excess of calcium is conditioned by the phosphorus content of the diet and that as this is increased it is necessary to increase the calcium content also, if good hatchability is to be obtained. Suitable levels of calcium and phosphorus intake for both good egg production and hatchability are given farther on (p. 814).

Manganese

Shortly after it was found by poultry-nutrition investigators at Cornell University that perosis ^^ was due, at least in major part, to a deficiency of manganese, Lyons and Insko (705) reported that the hatchability on a basal diet which contained only about 6 parts per million of manganese wâs only about 5.2 percent and that the embryos exhibited many of the symptoms of chondrodystrophy which had been described by Byerly and associates (179). When, however, the same diet was fed after 40 parts per million of manganese had been added to it, the hatchability was increased to 49.4 percent and chondrodystrophy was eliminated. Lyons and Insko thus demonstrated that manganese plays an important role in the embryonic development

^ The standard unit for the measurement of vitamin G (riboflavin) potency is tlie microgram, or gamma, which is one-millionth of a gram or slightly less than one twenty-eight-millionth of an ounce. Most of the early assays of the vitamin G potency of poultry feeding stuffs were made by research workers in poultry nutrition at Cornell University. In these assays young growing chicks were used as the test animals and a unit of measurement which was dependent on the growth of the chicks was devised, This chick-grow^th unit has frequently been referred to as the Cornell chick unit. Later work showed that the original Cornell chick unit of vitamin G is approximately equal to 1 microgram of riboflavin.

10 Perosis is a condition in which there is faulty development of the skeleton, which is most readily observed in the bones of the legs. The symptoms are enlargement of the hock joints, bending and rotational twisting of the leg bones, and in advanced cases a slipping of the tendons from their normal position. The condition has been called '*hock disease" and "slipped tendons."


of the chicken. Their work and that of others indicates that for p:ood hatchability the diet should contain about 50 parts per milHon of manganese.

Selenium

The possibility that certain mineral elements, when ingested with the feed, may adversely affect embryonic development was clearly shown by Poley, Moxon, and Franke {929), These workers found that when a diet that contained about 15 parts per million of selenium (supplied by naturally grown grain) was fed for a period of 5 weeks, hatchability progressively decreased to zero. They also observed that 6 days after feeding of normal grain was instituted, the apparently toxic effects on embryonic development and on hatchabilit}^ disap- peared. ^ The practical importance of the findings of Poley, Moxon, and Franke is somewhat obscure at the present time, but it may be pointed out that there are a number of areas throughout the world in which the soil contains significant quantities of selenium.

Sunshine and Hatchability It has been known for a number of years that permitting chickens

to have access to sunshine has a beneficial effect on the hatchability of their eggs. The major part of this effect is undoubtedly due to the fact that when animals receive sunshine they are able to make at least a part of the vitamin D that they require. However, Smith {1074) obtained evidence that there is a difference in the degree to which sunshine improves the hatchability of eggs depending on the kind of protein supplement in the feed. This raised the question as to whether sunshine supplies another factor than vitamin D that is necessary for good hatchability. Somewhat later Byerly and associates {180) demonstrated that this was the case. With the diet used in their experiments, egg production was significantly greater in pens receiving direct sunlight than in confined pens adequately supplied with cod- liver oil. The exact nature of this factor has not yet been established.

Adaptation to Diet and the Effect of Age and Stage of Development on Hatchability Byerly, Titus, and Ellis {177) studied the hatchability of the eggs

produced by pullets that received diets in which the protein was derived solely from (1) wheat middlings, (2) corn and corn-gluten meal, and (3) soybean meal. Some of the pullets were fed these diets from the time they were hatched and some only after they had been raised to sexual maturity on a well-balanced diet. The hatchabiUty of the eggs from the pullets that were raised on these diets was signiè- cantly greater than that of the eggs from the pullets that were raised on the well-balanced diet. These workers concluded that this must mean that, of the birds reared on the diets in which the protein was derived from these single sources, those that were less able to utilize such restricted sources of protein died before they reached maturity. In any case, the writer suggests that it is desirable to feed to breeding stock diets composed of essentially the same feedstuff s as were used in the diet on which the chickens were raised.

On the other hand, the possibility must not be overlooked that the age or stage of development of chickens may affect their ability to


utilize certain diets. Byerly and associates {180) found that if pullets were fed diets in which the chief protein supplement was soybean meal, the percentage of hatchability of the resulting eggs progressively decreased from October to January, after which it again increased to relatively high levels. These same workers also found (results unpublished) that if the same diet were fed to yearling hens, there was no marked decrease in hatchability from October to January. Moreover, Titus and associates {114-2) observed that pullets and hens do not react in the same way to high and low levels of calcium intake. In their experiments the hens laid more eggs than the pullets on the least calcium but on the diets containing the most calcium the pullets laid more than the hens. They found that the deleterious effect of a high level of calcium intake on hatchability was more pronounced in the eggs from hens than in the eggs from pullets.

Time of Occurrence of Embryonic IVIortality

Byerly, Titus, and Ellis {177, 178) and Titus and associates {llJfl, 1142) have made extensive studies of the relation between the time of occurrence of embryonic mortality and diet. They observed that when the protein of the diet was derived chiefly from products of plant origin there was a marked increase in the second-week embryonic mortality. They also found that the percentage of embryonic mortality increased during the last 3 days of incubation if the calcium intake was increased to excessive levels and that this increase was greater when the phosphorus intake was 0.9 percent of the diet than when it was 1.2 percent. These same workers also observed that the inclusion of stick, or of a mixture of stick and blood meal, in the diet as the chief protein supplement markedly increased the mortality throughout the entire period of incubation, but that the increase was greatest after the tenth and eighth days, respectively.

It was found by Insko and Lyons {576) that the third-week embryonic mortality, which they observed when a diet deficient in vitamin D was fed, was markedly decreased when vitamin D was supplied. Lyons and Insko {705) also observed that the embryonic mortality during the third week was reduced more than 60 percent when manganese was added to diets that contained only a very small quantity of this element.

As previously noted, Barnuni {62) associated increased first-week embryonic mortality with vitamin E deficiency of the diet.

From the information available on the time embryonic mortality takes place it is evident that the mortality occurring during the third week may be caused by several different factors and thus is attributable to cumulative effects. On the other hand, the second-week mortality and, perhaps to an even greater extent, the first-week mortality, when attributable to diet, seem to be due to immediate causes.

NUTRITION AND EGG PRODUCTION IN THE CHICKEN

^ The e.gg of the chicken is normally a complete and balanced combination of all the nutritive elements required for the full development of the^ chick embryo. It contains everything necessary for the formation of blood, nerve, and brain; muscle, tendon, and bone; skin, nail, and feather; and enough nourishment to enable the chick to


break through its shell and survive for several days without feed. Moreover, the chicken egg is highly prized as human food.

The egg is readily separable into three parts—the white, the yolk, and the shell. The white in turn may be separated into four parts— an outer envelope of fluid white, an inner envelope of firm white, an inner envelope of fluid white, and a small portion of firm white that is attached to the yolk. The yolk consists of alternate, concentric layers of white yolk and yellow yolk. The shell is made up of several layers of calcium carbonate and an outer cuticle, or skin. Attached to the inner surface of the shell and separating the shell from the white are the outer and inner shell membranes. The white is separated from the yolk by the vitelline membrane which completely surrounds the latter.

COMPOSITION OF THE EGG

On an average, the white accounts for about 58 percent by weight of the whole egg, the yolk for about 32 percent, and the shell for about 10 percent. The white consists of nearly 87 percent of water, nearly 12 percent of protein, and very small quantities of fats, sugars, minerals, and other substances. The yolk contains about 49 percent of water, about 32 percent of fat, about 17 percent of protein, and comparatively small quantities of sugars, minerals, and other substances. The shell consists mostly of calcium carbonate but contains some organic matter, water, and mineral substances other than calcium carbonate.

The proteins in eggs supply all the amino acids necessary for growth and maintenance. The fats contain an appreciable quantity of at least one of the so-called essential fat acids, i. e., linoleic acid. The mineral elements always present in eggs include calcium, magne- sium, potassium, sodium, iron, aluminum, manganese, zinc, copper, lead, silicon, phosphorus, sulfur, chlorine, iodine, and fluorine; and traces of arsenic, boron, titanium, and vanadium have also been found.

In general, eggs are a good source of riboflavin (vitamin G), and a fair source of vitamin A and vitamin D; they also contain some vitamin Bi, vitamin E, and vitamin K. Although the fresh egg contains no vitamin C, it can be demonstrated that appreciable quantities are formed after the fourth or fifth day of incubation.

PHYSIOLOGICAL PROCESSES OF EGG FORMATION

The organs primarily concerned with the formation of the egg are the ovary and the oviduct. A short time before egg production begins several of the ova begin to grow, the calcium content of the blood increases two to two and one-half times, and finally one of the ova is released as a matured yolk. Upon its release from the ovary, or shortly thereafter, the yolk is grasped by the mouth of the oviduct and slowly forced toward the vent. As the yolk passes through the oviduct the white is laid down and then the shell is formed. By the time the egg reaches the end of the oviduct it is complete and ready to be laid. Between 14 and 16 hours are required for completing the egg after the ova is released. The time that elapses between the completion and the laying of an egg may vary from 10 to 14 hours;


however, when a chicken is producing heavily, about 24 to 26 hours elapse between the la3dng of consecutive eggs in a clutch.

The various physiological processes involved in the development of the ova and the oviduct, and in the laying down of the white and the shell, are not fully known. However, there is some evidence that a hormone secreted by the anterior lobe of the pituitary gland starts the development of the ova in the ovary and, in turn, the ovary appears to secrete a hormone that stimulates the development of the oviduct and keeps it in a functioning condition after it is fully de- veloped. The stimulus for the laying down of the white and the shell appears to be largely mechanical, that is to say, the presence of the yolk or of any small object in the oviduct first causes the white to be secreted and then the shell to be formed.

Egg production niay be quite markedly affected by the treatment of the chickens, by interruptions of the feed supply, and by environ- mental temperatures. Frequent handling of chickens, until they become accustomed to it, tends to decrease egg production. Moving them from one environment to another, especially during the early part of the molt, or just before, tends to cause a break in egg production. During the period of the molt, egg production is usually greatly reduced and in many instances is stopped entirely. Irregularity of feeding and the temporary withholding of the feed adverse^ affect production. Sharp drops in temperature may cause egg production to cease entirely for a few days or even several weeks. During periods of high temperature there is a tendency for the weight of the eggs to decrease, and if the temperature is sufficiently high egg production may decrease or even stop.

NUTRITIVE REQUIREMENTS FOR EGG PRODUCTION

Although the potential egg-laying capacity of a chicken is largely determined by its inheritance, the number of eggs laid, within this capacity, is dependent on the quantity and kind of feed eaten. A part of the feed consumed by a pullet is used for growth and the re- mainder for maintenance and egg production. In yearling and older hens, most of the feed is used for the last two purposes, but some is used for regaining the weight lost during the molt.

The economic maintenance requirement (p. 431) of White Leghorn pullets weighing 4 pounds is between 0.145 and 0.160 pound of feed per bird per day, and for pullets weighing only 3.6 pounds it is between 0.134 and 0.148 pound per bird per day. The economic maintenance requirement of chickens of the heavier breeds is appreciably greater; for example, in the case of Khode Island Red pullets that weigh e5K pounds it is between 0.205 and 0.227 pound per bird per day, and for pullets that weigh only 5 pounds it is between 0.186 and 0.206 pound per bird per day. The economic maintenance requirement of hens of any given live weight is essentially the same as that of pullets of the same live weight.

It has been found that after the growth and maintenance requirements have been taken care of, the quantity of feed required to produce an average 2-ounce egg is between 0.078 and 0.1 pound, or on an average about 0.09 pound. Apparently, the first determination of the quantity of feed required, in addition to the economic maintenance

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AVERAGE NUMBER OF EGGS LAID PER PULLET PER YEAR

Figure 2,—The more eggs a pullet produces in a year, ihe less leed is required per dozen eggs. A White Leghorn pullel producing fOO eggs a year consumes ahnost twice as much feed per dozen eggs as a pullet producing 200 eggs a year. (Data obtained in different years from two different lots of White Leghorn pullets at the U. S. Animal Husbandry Experiment Farm, Beltsville, Md., and from Md. Agr. Expt. Sta!

Bull. 359 {1178), Data graduated by the method of least squares.)

requirement, to produce an egg was made in 1928. This quantity of feed was found to be about 0.089 pound {1139). Ten years later Brody and others {löö) of the Missouri Agricultural Experiment Station made a detailed study of the efficiency of feed utihzation for Qgg production and found this quantity to be about 0.087 pound. The agi-eement between the two values is exceptionally good, but undoubtedly accidental.

Feed Cost and Efficiency of Egg Production

A more or less fixed quantity of feed is required per day for the maintenance of a laying chicken, no matter what its rate of egg production may be. The quantity required for the making of an egg is always less than this daily maintenance requirement. It follows that the total feed cost per egg is much less w^hen the average production of a flock is high than when it is low. It also follows that the eflaciency of egg production, that is, the number of eggs produced


per unit weight of feed consumed, increases as egg production increases.

The relation between the feed cost of a dozen eggs and the average annual egg production is shown in figure 2, in which the feed consumed per dozen eggs is plotted against the average number of eggs laid per bird per year. According to these curves a White Leghorn pullet will consume between 7.7 and 8.7 pounds of feed per dozen eggs, if she lays 100 eggs per year, but only from 4,4 to 4.9 pounds, if she lays 200 eggs. This clearly demonstrates the importance of hav- ing chickens that can be depended on to produce a large number of eggs.

Figure 3 shows the relation between the efficiency of egg production and the average number of eggs laid per bird per year. It shows very definitely that chickens of the heavier breeds lay fewer eggs per pound of feed than do those of the lighter breeds and indicates that pullets lay more eggs per pound of feed than do hens. Notwith- standing, it must be recognized that difi'erent strains of the same breed may be appreciably diflêrent in their ability to utilize feed for egg production, as is suggested by the three curves in figure 2. Q 4.25 ÜJ 2 4.00 CO

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AVERAGE NUMBER OF EGGS LAID PER BIRD PER YEAR

Figure 3,—The breed and the age of chickens affect the efficiency of feed utilization for egg production. Pullets are more efficient producers than hens; ihe lighter breeds are more efficient than the heavier breeds. (Data from U. S. Animal Husbandry

Experiment Farm, Beltsville, Md., graduated by the method of least squares.)


Specific Requirements It has been demonstrated several times that it is possible to com-

pound two diets on which the egg production will be practically the same but on which the hatchability will be very different. It has been found, however, that the eggs of chickens that lay a large number tend to hatch better than those of chickens that lay a much smaller number. This suggests that it is always best to feed diets that will permit the chickens to produce eggs of high hatchability, because poor hatchability may be the result of a dietary deficiency too slight to decrease egg production but suiBcient gradually to undermine the health of the chickens. The nutritive requirements for good hatchability have already been discussed; the specific nutritive requirements of chickens for egg production follow.

That egg production is dependent on the nature of the diet may be demonstrated easily in a number of ways. If nothing but grain is fed, a high level of egg production cannot be maintained because grain usually does not supply enough protein and that which it does supply is not of suitable quality. If the diet contains too little calcium, egg production ceases rather promptly; and if the chickens do not get enough vitamin D they cannot properly use a, supply of calcium that would otherwise be adequate. Also, if the diet is deficient in vitamin A, the general health of the chickens will be adversely affected and egg production will decline or cease entirely. According to the existing knowledge about poultry nutrition, if the diet furnishes enough protein of good quality and adequate supplies of the necessary minerals and vitamins, it is suitable for egg production, provided it contains no harmful ingredients.

Protein Requirements

An egg that weighs 56.7 grams (2 ounces) contains slightly more than 7 grams of protein of very high biological value, or quality; to produce such an egg a chicken requires from 10.5 to 12.5 grams of digestible protein; and to supply this, 12.5 to 15 grams of feed protein of good quality is required. Inasmuch as the chicken has a rather limited capacity for storing protein that can be used for making eggs, the feed consumed each day should furnish not less than 12.5 grams of protein of good quality, if a constantly available supply thereof for making eggs is to be maintained.

It has been found that very good egg production—200 eggs or more per year—may be obtained on diets containing as little as 12 to 13 percent of protein. In spite of this, it has been observed that egg production, especially in pullets, tends to increase as the protein content of the diet is increased from 13 to 18 or even 20 percent. Several groups of investigators have found that both live wêight and good egg production can be maintained on diets containing 15 percent of protein. It is safer, however, to rely on a protein content between 16 and 17 percent. This is particularly true in the case of pullets during their first 4 months of egg laying, when protein is required for both growth and egg production.

What has just been said about suitable percentages of proteins in the diet for egg production applies only when the protein is of good quality. To insure that the protein will be of suitable quality, not


less than 20 percent of it should be from feedstuiïs of animal origin such as liquid skim milk, liquid buttermilk, dried skim milk, dried buttermilk, meat scrap, and fish meal.

Mineral Reqûirements

A chicken that la^^s 200 eggs per year puts into those eggs about 400 grams of calcium or about 13 to 15 times as much as there is in her entire body. If the diet is deficient in calcium, a chicken can draw on its skeleton for only enough calcium to make about 3 or 4 eggs. From this it is evident that the calcium requirement of laying chickens is very high and that the feed must supply virtually all the calcium that goes into the eggs.

The proper percentage of calcium in the diet is dependent on (1) the number of eggs laid per bird, (2) the quantity of feed consumed, and (3) the phosphorus content of the diet. Inasmuch as the laying chicken can readily adapt her physiological processes to diets that contain somewhat more calcium and phosphorus than she needs, it is possible to set up standards for the calcium and phosphorus content of the diet that will be applicable under all ordinary conditions. Table 1 shows approximately how much calcium diets of different phosphorus content should contain.

TABLE 1.—Corresponding approximate percentages of phosphorus and calcium for all' mash diets and for laying mashes with ivhich grain is to be fed

All-mash diets Laying mashes

(with which grain is to be fed)

A-ll-mash diets Laying mashes


Ali-mash diets Laying mashes


Phos- phorus

content

Cal- cium

content

Phos- phorus content

Cal- cium

content

Phos- phorus

content

Percent 0.9 1.0 1.1

Cal- cium

content

Percent 2.3 2.4 2.5

Phos- phorus

content

Cal- cium

content

Phos- phorus

content

Cal- cium

content

Phos- phorus content

Cal- cium

content

Percent 0.6 .7 .8

Percent 1.9 2.0 2.1

Percent, 0.8 .9

1.0

Percent 3.7 3.8 3.9

Percent LI 1.2 1.3

Percent 4.1 4.2 4.3

Percent 1.2 1.3

Percent 2.7 2.8

Percent 1.4 1.6

Percent 4.4 4.6

Occasionally the feed of laying chickens may contain too little phosphorus, especially if it contains very little dried skim milk, dried buttermilk, meat scrap, meat-and-bone scrap, or fish meal. In case the total phosphorus content of the diet is appreciably less than 0.7 percent, enough steamed bonemeal should be added to bring it up to at least this value.

Ordinarily the feed consumed by laying chickens does not contain enough salt unless some is added. The quantity to add depends to some extent on the other ingredients of the feed mixture. If the feed mixture contains as much as 15 percent of meat scrap, meat-and-bone scrap, fish meal, or any combination of these feeding stuffs, not so much salt need be added as when other protein supplements are used. In any case, if the total feed contains about 0.5 percent of added salt, all the salt requirements of the chickens will be t\A\j met and there will be little likelihood of any harmful excess.

It has been found that many of the usual feed mixtures fed to poultry may not contain enough manganese. This deficiency can be niade up


by using in place of plain salt a mixture of 100 parts of salt and 1.7 parts of anhydrous manganous sulfate (or 2.5 parts of manganous sulfate tetrahydrate). One-half of one percent of this mixture in an all-mash diet can be depended on to supply enough salt and enough manganese; but in a laying mash with which grain is to be fed 1 percent should be included.

Vitamin Requirements

Although the importance of several of the vitamins in the feeding of chickens has been recognized by poultry-nutrition workers for at least a dozen years, precise knowledge of the optimum requirements for egg production is still lacking. However, enough is known to enable one to state levels of vitamin intake that are adequate under ordinary conditions. If the eggs are not to be used for hatching, the following quantities of vitamins per pound of feed will usually be adequate: 3,150 International Units of vitamin A, 180 International Units of vitamin Bi, 360 A. O. A. C. chick units " of vitamin D, and 680 micrograms (gammas or Cornell chick units ^^) of riboflavin (vitaniin G). However, if the eggs are to be used for hatching, the following quantities per pound of feed are recommended: 4,720 International Units of vitamin A, 180 International Units of vitamin Bi, 540 A. O. A. C. chick units of vitamin D, and 1,250 micrograms (gammas or Cornell chick units) of riboflavin (vitamin G). As has been stated already, it is probably always best to feed diets that will permit the chickens to lay eggs of high hatchability ; the levels of vitamin intake that are recommended here for producing hatching eggs are therefore to be preferred to those given as being adequate for producing eggs not intended for hatching.

EFFECT OF DIET ON EGGS

As has been shown (p. 791), the diet of chickens affects the composition of the eggs and consequently their market value as human food.

It has been reported that certain feedstuiïs, such as onions, rape, turnips, and some fish meals and oils, if fed to chickens in excessive quantities, may have an undesirable effect on the flavor of the resulting eggs. However, if undesirable flavors are found in eggs, it is best to examine a few eggs from each individual chicken in the flock, because it has been found that an occasional bird produces eggs that have an objectionable flavor, regardless of the kind of feed consumed. If only a few chickens are found to be producing off-flavored eggs these should be removed from the flock. However, if the number of such chickens is quite large, the feed may be at fault and an attempt should be made to identify and eliminate the ingredient that is causing the trouble.

No acceptable evidence has been obtained that the feed aftects the physical properties, or the so-called ''quality,'^ of the white of eggs. On the other hand, the color of the yolk and the ability of eggs to stand up well in cold storage may be readily affected by diet. Very light- colored yolks may be obtained by eliminating green feed from the diet and by replacing the yellow corn with oats, barley, or white corn.

1Î See footnote 8, p. 796. 12 See footnote 9, p. 797.


The richer shades of yellow may be obtained through the use of yellow corn and alfalfa-leaf meal; and deep orange-red yolks may be obtained by feeding 0.5 to 2 percent of ground pimiento pepper or chili pepper. Cull peppers are best for this purpose because of their relative cheap- ness. Cull peppers may be fed also to increase yolk color in the winter when green feed is scarce or not to be had at all.

On some markets a premium is paid for eggs with yolks of light color, but ordinarily uniformity of yolk color is more important than lightness. The best method of obtaining yolks of uniform color is to feed a well-balanced all-mash diet and not permit the chickens to have access to green range. Both a grain mixture and a laying mash may be fed, however, if the ingredients of tlie grain mixture are so proportioned that it supplies about the same quantity of the coloring matters that affect yolk color as does the mash. The proper proportion of the ingredients of the grain mixture may be determined by trial—the maximum effect of any given diet on yolk color can usually be observed within a week after the diet is first fed.

Cottonseed meal tends to have an undesirable effect on the color of both the yolk and the white. If large quantities are fed the yolks of the resulting eggs may have a brown mottled appearance when laid. And even if small quantities—as little as 5 percent—are fed, the yolks tend to acquire a similar appearance after the eggs have been in cold storage for 6 weeks or longer. Cottonseed meal and weeds of the same botanical family as the cotton plant tend to produce a pink tint in the white. Eggs produced on diets containing cottonseed meal do not stand up well in cold storage; and in addition to the tendency for the yolks to become mottled, there is a tendency for the yolk membranes to become weakened.

The market value of eggs is also affected by the quahty of the shells. A deficiency of vitamin D in the diet affects the thickness of the shells and their abihty to resist breakage. A deficiency of calcium has the same effect. Also it has been claimed that a deficiency of manganese tends to cause the production of poor shells. Means of insuring against a deficiency of vitamin D, calcium, or manganese have already been discussed.

Egg soilage may also be affected by diet. A diet that tends to cause the droppings to be loose and watery also tends to increase egg soilage. Among the causes of loose droppings are too much salt and too much bran in the diet. Too much salt may be introduced through the use of fish meal of high salt content; such fish meals should not be used. To avoid the effect of too much bran, middlings may be substituted for a part of the bran. At times, the inclusion of 2 or 3 percent of linseed meal in the diet has the desirable effect of making the droppings less watery; more than this quantity should not be used, however, because it tends to have the opposite effect.

NUTRITIVE REQUIREMENTS FOR GROWTH AND FATTENING OF POULTRY

THE UTILIZATION OF FEED FOR GROWTH

As is generally known, the very young animal utihzes feed for growth much more efficiently than does' the nearly grown animal. As the


Hfiiirc I.—Kegiilar weighing of birds is nctcssury in llie sliidy of growth.


live weight of an animal increases there is a gradual but very definite decrease in the gain that results from the consumption of a pound of feed. This is due chiefly to the increase in the maintenance requirement, but it is also due in part to the change in the composition of the gain. The general relationship between live weight and feed consumption is illustrated by figure 2 (p. 451). Regular weighing of the birds is necessary in the study of growth. Figure 4 shows a young turkey being weighed in connection with growth studies.

It was formerly believed that animals consume less feed per pound of gain in live weight when they are allowed to eat all they want thaii when they are fed somewhat less than this quan tity. Ho we ver, Ellis a n d Zeller {3Ï9, 320) have shown that this is not true in the case of swine, and the work of Hammond, Hendricks, and Titus {468) clearly indicates that it is not true in the case of chickens. In an experiment conducted by the last-named investigators, seven lots of chickens were fed for a period of 52 weeks all they would eat of seven diets of different protein content, and another seven lots were fed 70 percent as much of the same diets. On each diet the feed was utilized more efficiently by the lot that was fed at the 70-percent level of feed intake. On the diet that contained the least protein (13 percent) the efficiency of the utilization of feed for growth was only about 4 percent greater at the 70-percent level than it was at the full-feed level, but as the percentage of protein in the diets increased the differences in efficiency became more and more pronounced. On the diet of highest protein content (25 percent) the efficiency was about 38 percent greater at the 70- percent level than at the full-feed level.

TABLE 2.—Effect in male chickens of the heavier breeds of the level of feed intake on the relative efficiency of utilization of feed for growth, the relative maximum live weight attained, the relative quantity of feed required for attaining the maximum live weight, and the relative length of time required to attain maximum live weight on a diet containing about

19.4 percent of crude protein

Level of feed intake as percent of full feed

30_. 40__ 50. _ 60__ 70-. 80. _ 90... 100.

Relative averapfe

efficiency of utilization

of feed for growth

Percent 90.7 93.3 97.2

100.0 99.] 96.8 94.8 93.1

Relative maximum

live weight 1 attained

Percent 19. J 51.1 77.7

100.0 114.9 127.7 138,3 148.9 150.6

Relative quantity

of feed required for attaining maximum

live weight '

Percent 21. 1 54,7 79.9

100. 0 116.0 131. 9 145.9 159.9 169.2

Relative length of

time required to

attain maximum

live weight 1

Percent 105. I 103. f) 101.0 100.0 98.1 94.9 89.9 82.0 73.2

1 This refers to the maximum live weight that is eventually attained after a prolonged period of feeding at the levels indicated in the first column.

In order to get additional information about the efiect of the level of feed intake on the efficiency of the chicken in utilizing feed for growth, the writer reexamined both published {114^) and unpublished data obtained with chickens at the Agricultural Research Center, Beltsville, Md. Some of the results of this reexamination are sum-


marized in table 2. This table contains data only for male chickens that were fed a diet which contained about 19.4 percent of protein. Apparently, the feed was utilized most efficiently for growth when the level of intake wâs between 50 and 60 percent of full feed. However, other data obtained by the writer indicate that the maximum efficiency is sometimes observed between the 60- and 70-percent levels. In any case, it may be concluded that a full-fed, growing chicken makes a smaller gain per pound of feed than a growing chicken fed at a much lower level of feed intake, if the diet contains between 13 and 25 percent of protein.

In the practical production of chickens for meat it would not be economical to feed growing stock at a level of feed intake that is only 50 to 60 percent of full feed, even though the feed is utilized more efficiently for growth at such a level. The data in table 2 indicate why this is true. According to these data it would require more than twice as much time, with the same brooding and housing facilities, to produce the same weight of live chickens at the 50-percent level of feed intake as it would at the full-feed level. Or, to state it another way, by feeding only 69 percent more feed at the full-feed level of intake one would get nearly 57 percent more live weight, in about 27 percent less time, than would be obtained by feeding at the 50-percent level. Moreover, the chickens that would be produced on this low level of feed intake would have little fat, and hence would have a lower market value per pound than those produced on full feed.

TABLE 3.—Quantities of feed required to obtain certain selected average live iveights with different kinds of poultry

Average live weight (pounds)

0.5_. 1.0_. 1.5_. 2.0.. 2.5.. 3.0. 3..5_. 4.0.. 4.Ó.. ñ.O..

Kind of poultry and quantity of feed required per bird

White Leghorn chickens

(males and females) '

Cross-bred 2 chickens (males)

Rhode Island Red chickens (males)

Turkeys 3 (males)

Pounds 1.20 3.18 5.27 7.75

10.80 14.75 20. 39

Pounds Pounds Pounds 1.29 1.12 0.95 2.91 2.53 2.20 4.65 4.05 3.49 6.52 5.69 4.83 8.56 7.49 6.21

10.78 9.46 7.65 13.24 11.66 9.15 15.97 14.13 10.70 19.07 16.95 12. 32 22.62 20.25 14.02

! White Pekin

: ducks , (males and ; females) '

Pounds 0.83 2.01 3.28 4.66 6.17 7.83 9.68

11.77 14.17 16.99

1 For a group containing approximately the same number of birds of each sex. 2 The male offspring resulting from mating Barred Plymouth Rock females to Rhode Island Red males. 3 Several different breeds from parent stock which had been selected for small size.

All breeds of chickens are not equally efficient in their utilization of feed for growth; likewise different kinds of poultry are not equally efficient. According to the few data that are available, both ducks and turkeys are more efficient than the heavier breeds of chickens, which in turn are more efiBcient than the lighter breeds. Some data on the feed required to obtain certain selected average live weights with different kinds of poultry are given in table 3. Since no two of the diets that were fed in obtaining these data were the same, it is not


possible to make exact comparisons of the efficiencies of the different kinds of poultry in utilizing feed for growth. Nevertheless, diets suitable for each kind of poultry were fed, and hence the data indicate in a general way the relative abilities of chickens, turkeys, and ducks to utilize feed for growth.

NUTRITIVE REQUIREMENTS FOR GROWTH

On the nineteenth or twentieth day of incubation the yolk sac is drawn into the body of the embryo and on the twenty-first day a fully formed chick is normalh^ ready to emerge from its shell. Whether or not the embryo develops into a fully formed chick is dependent to a considerable extent on the diet that was consumed by the mother. Likewise the viability of the hatched chick is dependent, at least íTI part, on the diet of the parent stock. The unabsorbed yolk in the body of the hatched chick is a concentrated reserve supply of nutrients on which the chick may subsist for several days even, though it receives no feed. Experience has shown, however, that it is best to supply both water and feed when the chick is about 1 day old, while it still contains some unabsorbed yolk.

If the diet of the newly hatched chick is deficient in proteins, vitamins, minerals, or the energy-producing nutrients, carbohydrates and fats, growth will be retarded and development will be abnormal. If the deficiency is great enough, the chick soon dies. From the standpoint of nutrition, the most critical period in the life of a chick is the first few weeks after hatching (fig. 5). It is during this period that special care should be taken to feed a diet that is fully adequate for the maintenance of health and growth. However, it is good husbandry to provide such a diet throughout the entire growing period.

If the diet is composed of the feedstuffs usually fed to chickens and if it furnishes enough protein of good quality and adequate supplies of the necessary ^minerals and vitamins, it is not likely to be deficient in carbohydrates or fats; and if it is not too finely or too coarsely ground and contains no harmful ingredients, it is suitable for feeding to growing chicks. Hence, in devising diets for growing chicks special attention should be given to the matter of supplying the proper quantity of protein of good quality and fully adequate but not excessive quantities of minerals and vitamins.

Protein Requirements Many workers at the State experiment stations in this country

have studied the protein requirements of growing chickens and a largo amount of information has been accumulated on this important subject. The majority of these workers are in agreement that the optimum percentage of protein in the diet of young growing chickens is not less than 18 or 19 percent, and several of them concur in the belief that the protein content of the diet should be decreased as the chicks become older.

One of the more recent studies of the effect of the percentage of protein in the diet of chickens on their growth and utilization of feed is that of Hammond, Hendricks, and Titus (4^8). Their data have been carefully graduated and the results are given in table 4. The figures in the second column of this table indicate that as the protein content


Figure 5.—From the standi)oint. of nutrition, the most critical period in the life of a chick IS the first few weeks after hatching.


of the diet increases from 13 to 21 percent there is a definite increase in the average efl&ciency of the utihzation of feed for growth, but as the protein content increases from 21 to 25 percent there is a rather sharp decrease in the efficiency. ^ Whether the optimum level of protein intake is exactly 21 percent, as indicated in table 4, or some slightly lower value, cannot be determined from the data, but the optimum level is very probably between 20 and 21 percent. Undoubtedly the optimum level varies with the biological value of the protein,'^^ being somewhat less for protein of a high biological value.

TABLE 4.—Effect in the male chicken of the leve] of protein intake on the relative efficiency of the utilization of feed for growth, the relative maximum live iveight attained, the relative quantity of feed required for attaining the maximum live weight, and the relative length

of time required to attain the maximum live weight

Relative Relative Relative quan- Relative Relative quan- Relative

Relative average Relative tity of length Relative average Relative tity of length level of effi- maxi- feed re- of time level of effi- maxi- feed re- of time protein ciency mum quired required protein ciency mum quired required

intake as of the live for at- to attain intake as of the live for at- to attain percent of utiliza- weight 1 taining maxi- percent of utiliza- weight J taining maxi- total feed tion of at- maxi- mum total feed tion of at- maxi- mum consumed feed for tained mum live consumed feed for tained mum live

growth live weight 1

weight 1

growth live

weight 1 weight 1

Percent Percent Percent Percent Percent Percent Percent Percent 13 67 7 97 6 144 1 119 9 20 99 7 99 8 100.1

100.0 100.5 100.0 14 80.6 97.9 121. 8 111.7 21 100.0 100.0

15 87 3 98 2 112 5 107 8 22 97 9 100 '^ 102.3 106 4

99.7 99.5 99.4

16 91.5 98.6 107* 7 104 6 23 94 3 100 4 17 94.6 98.9 104.6 102. 6 24 90.2 ioo! 5 111.4 18 97.2 99.2 102.1 101.5 25 85.6 100. 6 117.6 99 2 19 98.7 99.5 100.7 101.0

1 This refers to the maximum live weight that is attained when the birds are fully grown.

Apparently the level of protein intake, so long as it is not less than about 13 percent of the total feed consumed, has little effect on the maximum live weight ultimate^ attained; however, the time required to reach the maximum live weight is greatly increased as the level of protein intake is decreased from 21 to 13 percent. As the level of protein intake is increased from 21 to 25 percent there is only an insignificant decrease in the time required to reach the maximum live weight.

Even though the optimum level of protein intake is, from the physiological standpoint, about 21 percent, from the standpoint of economy it may be only 18 or 19 percent, because the efficiency of feed utilization for growth is only slightly less at these levels than it is at the 21- percent level. In most cases the difl'erence in cost between a diet that contains 21 percent of protein and one that contains only 18 or 19 percent will be an important factor in determining the most economical level of protein intake. In any case, the writer has found that it is a good practice to feed a diet that contains 20 to 21 percent of protein until the chickens are about 12 weeks old and then to gradually decrease the protein content to about 16 or 17 percent by the time the pullets are ready to lay. The pullets may then be placed on a diet that contains about the same quantity of protein, that is, 16 to 17 percent, but which is more suitable for the production of eggs.

13 See the article on Protein Requirements of Man, p. 173.


The protein requirement of young growing tin-keys (fig. 6), according to the few data available on the subject, is nearly 20 percent greater than that of young growing chickens. The optimum level of protein intake is about 25 percent for the first 12 weeks, but after that it may be reduced gradually to about 17 by the time the turkeys are 24 weeks old, and then to 14 or 15 by the time they are ready for market. After the thirtieth week the turkeys that are being kept as breeding stock may be fed a diet that contains only 13 or 14 percent of protein; but about a month before eggs are to be obtained for hatching, the protein content of the diet should be increased to about 16 or 17 percent and held there until the breeding season is over.

Mineral Requirements After reviewing the literature on the calcium and phosphorus

requirements of farm animals, Mitchell and McClure (803) concluded that the young growing chicken's average minimum requirements for these elements are represented by concentrations of about 0.70 to 0.75 percent of calcium and about 0.4 percent of phosphorus in the diet. From the studies of Mussehl and Ackerson (833) it may be concluded that the minimum requirement of turkeys for calcium is about the same as that of chickens, or possibly slightly greater.

In the practical feeding of poultry it is desirable to guard against possible deficiencies by feeding somewhat more of all the necessary nutrients than the minimum quantities required. This is true of the several mineral elements, as it is of protein and the vitamins, but, especially in the case of minerals, care should be taken not to supply too much. Although there is little accurate information about the optimum calcium and phosphorus requirements of growing chickens and turkeys, it is possible to state levels of intake that can be depended on to give satisfactory results.

A satisfactory level of phosphorus intake is 0.7 percent of the diet, but many practical diets contain much more than this. Since the utilization of calcium is intimately associated with that of phosphorus, it is desirable to know what the level of calcium intake should be for any given level of phosphorus intake. Apparently the chicken can readily excrete the excess calcium and phosphorus in any ratio from about 1.3:1 (1.3 parts calcium to 1 part phosphorus) to about 2:1 (2 parts calcium to 1 part phosphorus). Also, according to the studies of Ackerson and associates (9, 10, 11, 12,13), the ratio of the retained calcium to the i-etained phosphorus varies in the young growing chicken from 1.3:1 to nearly 1.7:1, with an average value of about 1.5:1. From this it may be concluded that the ratio of calcium to phosphorus in the diet may vary from 1.3:1 to 2:1. The optimum ratio is probably between 1.5:1 and 2:1, and experience has shown that a ratio of about 1.6:1 is quite satisfactory. Therefore it may be considered a good practice to have the diets of both chickens and turke^^s contain not less than 0.7 percent of phosphorus and to adjust the calcium content so that there is about 1.6 times as much calcium as phosphorus.

So far as is known, the salt requirements of growing chickens and turkeys are about the same as those of laying chickens (p. 805), or about 0.5 percent of added salt.

Figure 6.—The prolein requiremeiil of young growing turkeys is apparently almost 20 percent greater than thai of young growing chickens. ¡^

81Ó YEARBOOK OF AGRICULTURE, 1939

The optimum quantity of manganese in the diet is about 50 parts per million, or 50 milligrams per kilogram (p. 797). Inasmuch as certain types of diets commonly fed to poultry may not contain this much manganese, it is a good practice to guard against a possible deficieucy by adding about 30 parts per million. One-half of one percent of a mixture of 100 parts of salt and 1.7 parts of anhydrous manganous sulfate (or 2.5 parts of manganous sulfate tetrahydrate) is sufficient in all-mash diets, but in growing mashes as in laying mashes with which grain is to be fed 1 percent should be included.

There is no acceptable evidence that the usual diets fed to chickens or turkeys are likely to be deficient in any of the mineral elements other than those just discussed.

Vitamin Requirements During recent years the vitamin A requirement of growing chickens

has been carefully studied {951^ 969), and it is now possible to state both the approximate minimum requirement and the approximate optimum level of intake. The minimum requirement is about 150 International Units of vitamin A per 100 grams of feed, or about 780 units per pound. The optimum level of intake is at least 320 Inter- national Units of vitamin A per 100 grams of feed, or about 1,450 units per pound. Several times this quantity may be fed without harm; and when somewhat more than this quantity can be supplied at no appreciable increase in the cost of the feed, it is recommended that this be done.

The vitamin A requirement of growing turkeys has not been determined as carefully as has that of growing chickens. However, the relatively little information that has been obtained on the vitamin A requirements of turkeys indicates that they require at least 2 to 2K times as much as chickens. Hence a suitable, practical level of vitamin A intake for growing turkeys would be about 800 International Units of vitamin A per 100 grams of feed, or about 3,630 units per pound.

The minimum vitamin Bi requirement of growing chickens is about 20 International Units per 100 grams of feed; however, it is well to feed diets that contain about 40 units per 100 grams, or about 180 International Units per pound. So far as is known the vitamin Bi requirement of growing turkeys is essentially the same as that of growing chickens.

The growing chicken's requirement for vitamin D has been studierl more extensively than has its requirement for any of the other vitamins. Most of the workers agree that the minimum requirement is between 15 and 20 A. O. A. C. chick units of vitamin D per 100 grams of feed, but the studies of Couch, Fraps, and Sherwood (230) indicate that for certain levels of calcium and phosphorus intake the minimum requirement may be appreciably less. However, the optimum level of vitamin D intake is probably as much as 40 A. 0. A. C. chick units per 100 grams of feed, or about 180 A. O. A. C. chick units per pound.

According to Baird and Green (54) the growing turkey requires between 60 and 70 A. O. A. C. chick units per 100 grams of feed, which is appreciably more than the growing chicken requires. The optimum level of vitamin D intake for young growing turkeys is


probably about 80 A. O. A. C. chick units per 100 grams of feed, or about 360 A, O. A. C. chick units per pound.

It is very probable that the young growing chicken requires vitamin E for normal growth and development but its requirement for this factor has not been determined. Most poultry-nutrition workers agree that good, typical diets for growing chickens contain all the vitamin E that is required and that it is both unnecessary and a waste of money to use such expensive sources of vitamin E as wheat- germ oil to increase the vitamin E content of the diet. In any case, dependable information about the growing chicken's vitamin E requirement is very desirable and should be obtained.

D-ribofiavin, or riboflavin, is sometimes referred to as vitamin G. The growing chicken has a relatively high requirement for this vitamin. Most of our knowledge of the vitamin G requirement of growing chickens has resulted from the studies of Norris and associates (862) at Cornell University. The proper level of vitamin G intake for young growing chickens appears to be about 370 micrograms (gammas) of riboflavin per 100 grams of feed, or about 1,670 micrograms of riboflavin per pound. Apparently, young growing chickens and turkeys have about the same vitamin G requirement.

Certain fat acids, that is, linoleic, linolenic, and arachidonic acids, have been referred to as vitamin F. Whether or not the growing chicken requires these fat acids is not known. In addition to the vitamins which have been discussed here, the growing chicken requires the (1) chick antidermatosis factor, (2) vitamin K, (3) the anti-gizzard- erosion factor, and probably (4) vitamin B4. There is, however, little information about the quantitative requirements of the growing chicken for the last three of these four factors. According to the available information, the feed of growing chickens should contain about 0.9 modified Jukes-Lepkovsky unit ^^ of the chick antidermatosis factor per pound.

NUTRITIVE REQUIREMENTS OF CHICKENS BEING FINISHED (FATTENED) FOR MARKET

The nutritive requirements of chickens that are being finished, or fattened, for market depends on their age. Broilers should be fed essentially the same kind of diets that are usually fed to growing chickens, but roasters, capons, and fowls are best finished on diets that contain considerably less protein.

Ordinarily no advantage is gained by feeding broilers a special finishing diet; however, fish oils and fish meals are best omitted from the diets of growing chickens about 2 weeks before they are to be marketed, or the flesh of the chickens may have a fishy taste. Some- times, however, a special diet is fed to broilers for several days before they are killed. This is done primarily for the purpose of improving the market quahty and hence the value of the carcass. Finishing diets for broilers should contain about 18 percent of protein (air-dry basis), and they should possess all the nutritive properties of a growing diet but need not contain any special sources of vitamin D. How- ever, when the finishing diet contains no source of vitamin D, it is necessary for the dietary calcium-phosphorus ratio to be increased to

14 This unit for the measurement of the quantity of chick antidermatosis factor in feeding stuffs is desig- nated as the Jukes-Lepkovsky unit because these two workers at the University of California were the first to devise a method of assaying foodstuffs for this factor.

141304°—39 53


about 2.3:1 to prevent the development of brittle wing and leg bones. Diets for finishing roasters, capons, and fowls need not contain

more than 14 to 15 percent of protein. The quantities of the several vitamins may be reduced to about one-half of those recommended for growing chickens. It is desirable that the calcium and phosphorus content of diets for finishing these classes of market chickens be about 1 and 0.5 percent, respectively, or in the ratio of about 2 to 1.

Finishing diets should contain between 6 and 10 percent of fat (air- dry basis). Most finishing diets for market poultry do not contain this much fat, so it is a good practice to add some. Corn oil has been found to be quite well suited for this purpose, although if the finishing period is proloriged it tends to make the skin of the birds yellow, which is not desirable on some markets. Other oils, such as red palm oil, rapeseed oil, and peanut oil may be used. The quantity of oil to add to a finishing diet depends on its fat content; ordinarily the proper amount is between 2.5 and 6 percent,

SUMMARY OF THE NUTRITIVE REQUIREMENTS OF CHICKENS AND TURKEYS

The nutritive requirements of chickens and turkeys are summarized in table 5. In using this table reference should be made to the text. It will also be desirable to refer to the article that deals with the practices and economics of feeding poultry (p. 819).

TABLE 5.—Requirements of different classes of chickens and turkeys for protein, minerals and vitamins for satisfactory growth and development under various conditions observed

in practice

CHICKENS

Class

I

Protein i as proportion of total

feed

Growing chicks Laying stock... Breeding stock.

Growing poults. Breeding stock.

Percent 21 16 16

Phos- phorus as proportion of total

feed

Percent 0.7 1.0 1.0

Calcium as proportion of total

feed

Manga- nese in total feed

Vitamin A per pound

Vitamin B per pound

Inter na- Parts per tional

Percent million Units 1.1 50 1,450 2.4 50 3,150 2.4 50 4,720

of total i of total feed 2 I feed

Interna- tional Units

180 180 180

Vitamin D per pound of total

feed

A.O.A.C. chick units

180 360 640

Vitamin G (riboflavin)

per pound of total

feed

Gammas (or micro-

grams) 1,670

680 1,250

TURKEYS

1.0 1.0

1.6 2.4 4,720

180 180

360 540

1,670 1,250

1 The protein must be of reasonably good quality: and it is desirable that not less than derived from animal sources.

2 If the feed is to be stored for more than should be derived from plant sources-

percent be

month before it is fed, not less than 70 percent of the vitamin A

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PRACTICAL NUTRITIVE REQUIREMENTS OF POULTRY

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