Soyhulls as an Alternative Feed for Lactating

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REVIEW: SOYHULLS FOR DAIRY COWS 1053

Consequently, one could anticipate that the increasingavailability of SH in the US will promote their utiliza-tion in diets for ruminant animals.

Feed costs account for 35 to 50% of the total costs toproduce milk (Hutjens, 2001). Thus, dairy producersattempt to minimize the costs of feeding their herds,particularly when milk prices are low, in order to max-imize the efciency of production. In several areas of theUS, SH are readily available and usually at competitiveprices; hence, feeding this byproduct to dairy cows mayrepresent an excellent opportunity to reduce feed costs.

In addition to the potential of providing an economi-cal alternative, replacing cereal grains with SH in dietsfor dairy cows may contribute to elevated intakes of energy while preventing a disruption of rumen func-tionality. Alternatively, SH can be successfully used asa source of ber in rations for dairy cattle when forageseither are of poor quality or are in short supply.

In view of the aforementioned reasons and others, itappears that feeding SH to dairy cows, and to otherruminants, is a practice that will continue to increasein popularity among nutritionists and producers of ru-minant animals.

The objectives of this paper are to review the currentknowledge regarding the potential nutritional value of SH for lactating dairy cattle and the effects of replacingcereal grains or forages with SH on ruminal fermenta-tion, nutrient digestion and utilization, and productionby dairy cows. This review will also point out areaswhere additional research is needed to enhance SHutilization by lactating dairy cows.

NUTRITIONAL VALUE OF SH

Chemical Composition

In part, the nutritional value of SH for ruminants isdetermined by the chemical nature of the hulls. As formany other byproduct feeds, the chemical compositionof SH usually varies widely among processor plants(Belyea et al., 1989; Arosemena et al., 1995; DePeterset al., 1997). In some cases, part of this variation canbe explained by the misclassication of SB mill run andSB mill feed as SH (Titgemeyer, 2000). Whereas SBmill run and SB mill feed contain a portion of meat and

hulls, SH are composed mainly of pericarp (i.e., seedcoat). Other factors presumably associated with the variable chemical composition of SH include the follow-ing: differences between and within processing methods(DePeters et al., 1997), lack of rigorous quality-controlprograms during the production and handling of by-product feeds (Belyea et al., 1989), genetic differencesamong plant materials (Westgate et al., 2000), and dif-ferences in cultural (e.g., planting date and nitrogenfertilization) and environmental (e.g., temperature and

Journal of Dairy Science Vol. 86, No. 4, 2003

Table 1. Chemical composition of soyhulls. 1

Item Minimum Maximum Mean SD n

(%)CP 9.4 19.2 11.8 2.3 27 ADF 39.6 52.8 47.7 3.9 27NDF 53.4 73.7 65.6 5.0 27Cellulose 29.0 51.2 43.0 8.4 5Hemicellulose 15.1 19.7 17.8 2.7 3Uronic acids 2 11.1 14.8 13.0 2.6 2 ADL 3 1.4 3.9 2.1 0.8 13NSC 5.3 12.8 7.9 3.4 4Starch 0.0 9.4 2.9 3.2 8EE 0.8 4.4 2.7 1.6 9

1Data from: Quicke et al., 1959; Nocek and Hall, 1984; Hsu et al.,1987; Anderson et al., 1988; Garleb et al., 1988; Belyea et al., 1989;Nakamura and Owen, 1989; Cunningham et al., 1993; Shain et al.,1993; Faulkner et al., 1994; Manseld and Stern, 1994; Arosemenaet al., 1995; Bhatti and Firkins, 1995; Piwonka and Firkins, 1996;Stone, 1996; DePeters et al., 1997; Garce s-Yepez et al., 1997; Batajooand Shaver, 1998; Miller and Hoover, 1998; Mowrey et al., 1998;Bach et al., 1999; Mulligan et al., 1999; van Laar et al., 1999; Shiveret al., 2000; Miron et al., 2001; Ipharraguerre et al., 2002a, 2002b.

2Determined by colorimetric assay (Blumenkrantz and Asboe-Han-sen, 1973).

3 Acid detergent lignin.

water supply) conditions during SB growth (Westgateet al., 2000).

The chemical composition of SH reported in severalresearch publications is summarized in Table 1. Mironet al. (2001) found that carbohydrates, predominantlypolymers of glucose, make up approximately 80% of theDM in SH and that most of these carbohydrates ( 75%)derive from polysaccharides recovered in the NDF frac-tion. This is because the hulls, whose primary functionis to protect the endosperm of the SB, consist mainlyof thick cell walls ( 62% of SH DM [van Laar et al.,1999]). According to the NRC (2001), SH contain 60.3%NDF and 44.6% ADF on a DM basis. Nevertheless, theber content of SH has been shown to be variable (Table1), and this variation seems to be directly related tothe meat content of the products classied as SH (Tit-gemeyer, 2000). For instance, Anderson et al. (1988)found that well-cleaned SH contained 73.7% NDF and50.8% ADF, whereas DePeters et al. (1997) reportedthat SH, which apparently contained some meat, had

57.5 and 45.4% NDF and ADF, respectively. The berfraction of SH, which contains relatively large quanti-ties of both cellulose ( 43% of SH DM) and hemicellu-lose ( 18% of SH DM), is poorly lignied (Table 1). Thelignin content of SH ranged from 1.4% (Mulligan et al.,1999) to 3.9% (Anderson et al., 1988) when measuredas acid detergent lignin and averaged 4.3% (Hsu etal., 1987) when measured as permanganate lignin. Inaddition, SH have low concentrations of ferulic and p-cumaric acids, which are the primary phenolic mono-


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IPHARRAGUERRE AND CLARK1054

mers involved in the cross-linking between lignin andhemicelluloses (Garleb et al., 1988).

There are few studies in which the NSC or starchcontent of SH has been measured (Table 1). Although very low or even negligible amounts of these carbohy-drates might be expected in SH, the starch content of SH has been shown to range from 0 (Hsu et al., 1987)to 9.4% (Batajoo and Shaver, 1998) and averaged 2.9%(Table 1). DePeters et al. (1997) calculated an averagecontent of about 20% nonbrous carbohydrates ( NFC )for three different batches of SH, which increased toabout 24% when corrections for ber-bound proteinwere made. When determined by an enzymatic method,however, the NSC content of SH seems to be consider-ably lower ( 8%; Table 1). This apparent discrepancyis largely caused by the considerable concentration of uronic acids or pectin substances in the cell walls of SH (Table 1), which are only accounted for by the NFC

fraction. In fact, pectin represents the largest propor-tion (62%) of NFC in SH, whereas starch (19%) andsimple sugars (19%) are only minor components(NRC, 2001).

The CP content of SH averaged 11.8% (Table 1),which is within the range (13.9% 4.6) reported bythe NRC (2001). In studies where SH were thoroughlycleaned, the CP percentage ranged from 9.4 (Andersonet al., 1988) to 9.6 (Shiver et al., 2000). On the otherhand, Batajoo and Shaver (1998) found that SH cancontain up to 19.2% CP, but they suggested that somemeat must have been present in the hulls because of their high concentration of starch (9.4%).

Similar to SBM, SH are a rich source of Lys (0.71 to0.72% of DM), but not of Met and Cys, which are evenmore decient in SH (0.30 to 0.33% of DM [Cunninghamet al., 1993; Degussa, 1996]). In comparison to proteinfrom SBM, CP from SH is lower in Arg ( 35%), Ile(27%), Leu ( 25%), Val ( 16%), Phe ( 28%), Thr(16%), and Trp ( 18%), but higher in Tyr ( 30% [De-gussa, 1996; Rackis et al., 1961]). On average, proteinfrom SH contains about 3.5% less nonessential AA thanSBM protein, but protein from SH has an uncommonlyhigh Gly content,which is about 48% higher than that of the SBM fractions (Rackis et al., 1961; Degussa, 1996).

The fat content of SH, measured as ether extract,has been shown to be highly variable (Table 1). Thereis not a clear relationship between the content of fat inSH and either their CP or NDF concentration (Titgem-eyer, 2000). Belyea et al. (1989), for instance, observedthat SH from three different sources averaged 4.3%ether extract, 72.5% NDF, and 11.8% CP, whereas DeP-eters et al. (1997) reported similar ether extract values(4.4%) in SH with signicantly lower NDF (57.5%) andhigher CP (13%) concentrations.


Ruminal Digestion Kinetics

The nutritional value of SH is affected by the rate atwhich they are digested in the rumen and by the rateat which they pass from the rumen to the lower gastro-intestinal tract (Firkins, 1997; Grant, 1997; Titgem-

eyer, 2000). Data from in situ and in vitro experimentshave shown that ruminal microorganisms are capableof extensively fermenting SH at high rates (Table 2).For example, in seven in situ studies (Table 2), the NDFfraction of SH was fermented at an average rate of about 5.6%/h, and, in four studies, total NDF disappear-ance averaged about 90% after 96 h of incubation. Ap-parently, the low content of lignin and phenolic mono-mers in SH (Garleb et al., 1988), as well as therelativelylarge thickness and particle size of SH cell walls (vanLaar et al., 1999), allow therapid and extensivefermen-tation of the ber fraction. However, when diets con-taining SH and concentrates are used, the in vitro andin situ digestion kinetics parameters (i.e., lag time, di-gestion rate, and extent) of SH do not remain constant(Firkins, 1997). Piwonka and Firkins (1996) found thatthe in vitro rate of digestion of SH was reduced when2 ml of a glucose solution (0.0721 g/ml) were added tothe incubation medium that contained 30 ml of inocu-lum and 0.5 g of SH. Sarwar et al. (1992) reported that,after 96 h of in situ incubation, the extent of digestionof NDF in SH decreased about 23% when thepercentageof concentrate (50% of ground corn) in the diet increasedfrom 61 to 73%. In addition, for a given source andamount of dietary concentrate, the digestion kineticscan vary markedly among sources of SH because of differences in their chemical or physical characteristicsor both.

Although fermentation of SH by ruminal microbes isrelatively rapid and almost complete, in vivo digestionof the SH is much lower than fermentation in vitro andin situ (Quicke et al., 1959; Johnson et al., 1962; Hintzet al., 1964; Hsu et al., 1987; Anderson et al., 1988).These differences were even greater when SH were fedalone or constituted the major ingredient of the diet.For example, Quicke et al. (1959) measured the in vitrodigestibility of cellulose and crude ber in SH after 48h as 96 and 97%, respectively. In contrast, when SH

were fed ad libitum as the sole feed to sheep, in vivodigestibility coefcients for cellulose and crude berwere 54 and 57%, respectively. In another early study(Johnson et al., 1959), the in vitro digestibility of cellu-lose present in feces from sheep fed soybran akes (i.e.,steam-treated SH aked by rolling) was considerablyhigher than the digestibility of fecal cellulose of sheepfed other roughages (60 to 80% vs. 0 to 20%). Thesendings suggest that the rate at which SH pass fromthe rumen to the lower tract may be too rapid to max-


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Table 2. Characterization of digestion of soyhulls in situ and in vitro.

Digestion parameters

Study Diet Extent, %/time, h Rate, h -1 Lag time, h

In situ DM disappearanceNocek and Hall (1984) 25% Hay crop silage,25% corn silage, 50.6/24 0.025 NR 1

50% concentrateHsu et al. (1987) Alfalfa hay 104.0/36 0.077 NRKerley et al. (1992) 39 to 93% brome hay, 0 to 58% soyhulls 95.5/96 0.044 NRDePeters et al. (1997) 70% forage, 30% concentrate 87.2/72 0.047 NRBatajoo and Shaver (1998) 55% al falfa si lage , 45% concentrate 97.7/72 2 0.039 NRMulligan et al. (1999) 15% forage, 85% concentrate 100.0/72 0.042 NR

In situ NDF disappearanceNocek and Hall (1984) 25% hay crop silage, 25% corn silage, 53.5/24 0.030 NR

50% concentrateHighll et al. (1987) 73% fescue hay, 27% soyhulls 95.6/96 NR NR Anderson et al. (1988) Alfalfa hay 95.0/96 0.074 NRSarwar et al. (1991) 27% forage, 73% concentrate 65.9/96 0.036 NR

39% forage, 61% concentrate 88.7/96 0.033 NRPantoja et al. (1994) 40% forage, 60% concentrate 95.7/96 0.046 4.9

40% forage, 55% concentrate, 5% fat 95.8/96 0.054 6.0DePeters et al. (1997) 70% forage, 30% concentrate 95.8/72 0.038 NR Abel-Caines et al. (1998) 50% forage, 48% concentrate, 2% fat 95.3/72 0.092 8.6

40% forage, 60% concentrate 95.8/72 0.103 8.3In vitro NDF disappearance Anderson et al. (1988) Alfalfa hay 93.0/96 0.060 NRBelyea et al. (1989) Alfalfa hay 87.0/36 0.113 NRBhatti and Firkins (1995) Grass and legume hay 82.8/96 0.033 5.7Piwonka and Firkins (1996) Alfalfa hay, 1 kg corn grain 94.6/96 0.031 11.3Trater et al. (2001) 40% forage, 30% sorghum grain, 30% corn grain 80.7/48 NR NR

1Data not reported or determined.2Predicted by nonlinear regression.

imize ber digestion by ruminal microbes. Nakamuraand Owen (1989) determined the fractional rate of pas-sage of SH in lactating dairy cows consuming diets in

which SH replaced corn to supply either 25 or 48% of the dietary DM. They reported that the rate of passageof SH was 8% faster when SH constituted 48% of thedietary DM; moreover, the rate at which SH exited therumen for diets that contained 25 and 48% SH (0.093/ h and 0.10/h, respectively) almost doubled that of theforage (0.054/h and 0.055/h). Even though differencesamong treatments were not signicant, Nakamura andOwen (1989) suggested that an 8% increase in the pas-sage rate could be enough to account for the lower di-gestibility of NDF and ADF observed for the diet thatcontained 48% SH.

The relatively rapid passage rate of SH can be ex-

plained by their small particle size and high specicgravity when hydrated (Titgemeyer, 2000). Based onthe small particle size of most nonforage ber sources,Grant (1997) postulated that the functional specicgravity of those feeds, and not their particle size, isthe most likely determinant of their ruminal rate of passage. Data from experiments with cattle suggestthat particles with specic gravity ranging from 1.2 to1.5 have the highest rate of passage (Murphy et al.,1989). For SH, Bhatti and Firkins (1995) reported that


their functional specic gravity remained between 1.48and 1.35 during 27 h of in vitro incubation. Weidnerand Grant (1994a) found that the initial specic gravity

of 60% of SH particles ranged from 1.2 to 1.4 and, after3 h of ruminal incubation, the specic gravity of mostof them increased above 1.4.

Nevertheless, rate of passage reects other factorsthat might affect intake and rumen characteristics,such as restricted feed intake and diet composition (Of-fer and Dixon, 2000; Poppi et al., 2000). Woods et al.(1998) observed an average decline of 14% in the digest-ibility of OM from SH as the feeding of a mixture of 85% SH and 15% hay (DM basis) increased from main-tenance to two times maintenance for cattle and sheep.Mulligan et al. (1999) hypothesized that the depressionin digestibility was the result of an increase in the

ruminal passage rate of SH as DMI was doubled. Totest this hypothesis, stulated steers were fed a dietthat contained 83% SH, 15% hay, and 2% SBM (DMbasis) at two DMI, maintenance and twice mainte-nance. Digestion of SH was depressed only 8% at thehighest DMI, and the rumen outow rate of SH wasincreased by about 12%. As expected, when DMI in-creased, the passage rate of SH increased; however, themagnitude of the increased passage rate, as well asthe resulting effects on ruminal ber digestibility, are


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apparently dependent upon some other factors. For ex-ample, lactating dairy cows were fed three diets, a con-trol diet in which alfalfa silage and corn silage (1:1, wt/ wt, DM basis) supplied 60% of the DMI or diets inwhich a portion of the DM from the silage mixture wasreplaced with 25% SH or with 25% SH plus 20% longalfalfa hay (Weidner and Grant, 1994a). Although notsignicant but biologically important, the rate of pas-sage of SH decreased by 16% when SH and long hayreplaced part of the silage mixture, as opposed to whenonly SH were substituted for part of the silage mixture.Inclusion of long alfalfa hay in the diet that contained25% SH increased the ruminal mat consistency, whichin turn may have retained potentially escapable parti-cles of SH through ltration and mechanical entangle-ment (Weidner and Grant, 1994a). In contrast, Trateret al. (2001) reported that replacing SH in SH-baseddiets ( 96% of dietary DM) with alfalfa hay to supply0, 10, 20, and 30% of the dietary DM fed in limitedamounts to steers (1.75% of BW) increased the exit ratefrom the rumen of the liquid and solid fractions. Inspite of the accelerated passage rates, the addition of alfalfa hay to the diet decreased DMI and had positiveassociativeeffects on the apparent total-tract digestibil-ity of DM, OM, and NDF. The authors suggested thatreplacing SH with alfalfa hay may have stimulatedrumination and the ow of saliva to the rumen, re-sulting in higher ruminal pH, ber digestion rates, anddilution rates. These observations suggest that the out-ow rate of SH from the rumen does not restrict theapparent total-tract digestibility of the diet when rumi-

nants are fed limited amounts of feed.Data indicate that the addition of coarse forage todiets that contained SH and were fed ad libitum re-sulted in large positive associative effects by increasingthe time that SH were retained in the rumen and,hence, the time allowed for ruminal fermentation. Un-der these conditions, diet composition seems to affectthe feeding value of SH by altering the consistency of the ruminal forage mat, which in turn inuences theirruminal retention time. On the other hand, when rumi-nants are limited-fed diets containing SH the relativelylow DMI negates any increase in the ruminal rate of passage that may be expected from the addition of SH

to their diets.

Physical Form

The physical form of SH is another factor that mayaffect their nutritional value for ruminants. Prior tofeeding, SH are normally ground, pelleted, or groundand pelleted to increase bulk density and reduce ship-ping cost. Anderson et al. (1988) evaluated the effect of physical processing methods on digestion and nutri-


tional value of SH for lambs and cattle. They fed dietsthat contained 38% corn stalkage, 3% molasses, 8%proteinconcentrate, and 51% SH that were ground (1.5-mm screen), pelleted (0.95 x 7.62-cm die), or not pro-cessed (i.e., whole) to lambs and observed that onlygrinding depressed digestibility of NDF (62, 61, and56% for whole, pelleted, and ground SH, respectively).However, the negative effects of grinding on digestibil-ity of SH were not evident when larger screen sizeswere used (3.2 and 4.8 mm). Likewise, the growth per-formance of steers fed ad libitum a forage-based dietsupplemented with either whole or ground SH was notimpacted by the physical form of the SH when steersreceived 1.05 kg/d of SH. In contrast, when the amountof SH increased up to 2.1 kg/d per steer, ground SHresulted in a lower gain-to-DMI ratio than whole SH(0.105 vs. 0.120). Thus, feeding ground SH at high DMImay result in negative associative effects because of reduced ruminal retention time (Anderson et al., 1988).Based on this limited information, it appears that onlyne grinding ( < 1.5 mm) diminishes the feeding valueof SH for ruminants.

PERFORMANCE OF LACTATINGDAIRY COWS FED SH

Replacing Cereal Grains with SH

The performance of dairy cows fed diets in which SHpartially or totally replaced cereal grains is summa-rized in Table 3. In most studies, SH provided less than25% of the dietary DM, except for four trials in which

SH provided more than 30% of the dietary DM (Conradand Hibbs, 1961; Nakamura and Owen, 1989; Sarwaret al., 1992; Ipharraguerre et al., 2002a). In 13 of the15 studies reviewed, the grain supplied in the concen-trate mix was either high-moisture or dry ground corn.Nearly all of these experiments, except for those of Pan-toja et al. (1994) and Elliott et al. (1995), were conductedto evaluate the effects of replacing a portion of the di-etary starch or NSC provided from corn with ber fromSH. However, only in one (Conrad and Hibbs, 1961)was the dietary content of starch reported, in three(Cunningham et al., 1993; Elliott et al., 1995; Stone,1996) dietary NFC content was calculated, and in three

others (Sarwar et al., 1992; Manseld and Stern, 1994;Ipharraguerre et al., 2002a) dietary NSC or total non-structural carbohydrates was enzymatically deter-mined.

Multiple regression analyses were conducted usingdata from selected studies to facilitate the interpreta-tion of the relationship between the performance of dairy cows and the substitution of SH for corn grain.Data from 10 studies (Macgregor and Owen, 1976; Na-kamura and Owen, 1989; Bernard and McNeill, 1991;


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Table 3. Performance of lactating dairy cows fed diets in which soyhulls replaced cereal grains or forages.

Study DIM Parity 1 Dietary treatments 2 DMI M

Soyhulls replaced grains (kg/d)Conrad and Hibbs (1961) 3 NR NR Ct: 44% MH, 16% CM, 28% O 17.4 19.6

NR NR T1: 24% MH, 28% CM, 48% SH 16.4 21.4*Wagner et al. (1965) 4 NR NR Ct: 23% AH, 49% CS, 19.5% CM, 8.5% O 29.7 22.6

NR NR T1: 23% AH, 49% CS, 19.5% CM, 8.5% SH 28.3 22.3 MacGregor and Owen (1976) NR M Ct: 44% AS, 48% GC 18.1 18.6

T1: 43% AS, 35% GC, 15% SH 19.1 19.6T2: 42% AS, 23% GC, 28% SH 18.6 18.5

Nakamura and Owen (1989) 130 M Ct: 50% AS, 45% GC 23.4 29.8 T1: 50% AS, 21% GC, 25% SH 23.8 28.9T2: 50% AS, 48% SH 24.0 27.

Bernard and McNeil (1991) 150 M Ct: 46% CS, 34% GC 21.3 27.7 T: 48% CS, 11% GC, 23% SH 22.5 27.7

Firkins and Eastridge (1992) 28 M, P Ct: 10% AS, 31% CS, 34% GC 24.4 37.0 T1: 10% AS, 31% CS, 13% GC, 20% SH, 11% RSB, 0.43% CaS 22.5 38.9

Sarwar et al. (1992) 57 P Ct: 22% AS, 22% CS, 38% GC 19.4 24.7 T1: 22% AS, 22% CS, 20% GC, 19% SH, 7% RSB 19.9 25.9T2: 22% AS, 22% CS, 4% GC, 34% SH, 13% RSB, 1% CaS 20.4 27.7

Cunningham et al. (1993) 31 M Ct: 10% AH, 40% CS, 25% HMC 24.1 37.4 T1: 10% AH, 40% CS, 14% HMC, 12% SH 22.7 35.5 T2: 10% AH, 40% CS, 2% HMC, 25% SH 23.2 35.8

Pantoja et al. (1994) 43 P Ct: 16% AS, 24% CS, 34% GC 19.3 29.5 T: 16% AS, 24% CS, 16% GC, 20% SH 17.8 27.3

Manseld and Stern (1994) 78 M Ct: 14% AH, 6% GH, 32% CS, 28% GC 20.2 28.7 T: 14% AH, 6% GH, 32% CS, 30% SH 20.7 27.7

Elliott et al. (1995) 29 M, P Ct: 22% AS, 22% CS, 36% GC 19.8 23.8 (Experiment 1, main effects) T: 22% AS, 22% CS, 18% GC, 18% SH 19.3 22.8

Elliott et al. (1995) 31 M Ct: 22% AS, 22% CS, 36% GC 23.5 24.5 (Experiment 2, main effects) 147 T: 22% AS, 22% CS, 18% GC, 18% SH 22.6 25.7

Stone (1996) 8 M Ct: 26% AS, 26% CS, 23% HMC 20.7 40.7 T: 26% AS, 26% CS, 9% HMC, 14% SH 22.6 41.7

Stone (1996) 8 P Ct: 26% AS, 26% CS, 23% HMC 16.6 31.5

T: 26% AS, 26% CS, 9% HMC, 14% SH 17.1 31.5Ipharraguerre et al. (2002a) 112 M Ct: 23% AS, 23% CS, 40% GC 23.8 29.5 T1: 23% AS, 23% CS, 30% GC, 10% SH 24.8 I 2T2: 23% AS, 23% CS, 21% GC, 20% SH 24.4 I 2T3: 23% AS, 23% CS, 11% GC, 30% SH 22.9 I 2T4: 23% AS, 23% CS, 1% GC, 40% SH 22.7 I 2

J o ur n al of D ai r y S c i en c eV ol . 8 6 ,N o.4 ,2 0 0 3


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Table 3. (continued) Performance of lactating dairy cows fed diets in which soyhulls replaced cereal grains or forages.

Study DIM Parity 1 Dietary treatments 2 DMI Milk

(kg/d)Soyhulls replaced forages

Firkins and Eastridge (1992) 28 M, P Ct: 10% AS, 31% CS, 34% GC 24.4 37.0 33.T1: 10% AS, 20% CS, 38% GC, 7% SH 23.5 37.3 T2: 10% AS, 20% CS, 37% GC, 7% SH, 1% NaB 23.2 35.1

Sarwar et al. (1992) 57 P Ct: 22% AS, 22% CS, 38% GC 19.4 24.7 2T1: 18% AS, 18% CS, 40% GC, 5% SH 19.8 24.2 T2: 16% AS, 16% CS, 41% GC, 9% SH 19.4 25.2

Cunningham et al. (1993) 31 M Ct: 10% AH, 40% CS, 25% HMC 24.1 37.4 34T1: 10% AH, 29% CS, 25% HMC, 12% SH 23.5 L 37.3 T2: 10% AH, 18% CS, 26% HMC, 25% SH 22.3 L 35.4

Pantoja et al. (1994) 43 P Ct: 24% AS, 36% CS, 17% GC 18.3 27.5 2T: 16% AS, 24% CS, 16% GC, 20% SH 17.8 27.3

Weidner and Grant (1994b) 34 NR Ct: 30% AS, 30% CS, 17% GC 23.2 31.9 30151 T1: 22% AS, 22% CS, 17% GC, 15% SH 22.5 31.5

T2: 17% AS, 17% CS, 15% GC, 25% SH 23.2 31.8 T3: 13% AS, 13% CS, 20% AH, 19% GC, 15% SH 22.3 30.0 T4: 7% AS, 7% CS, 20% AH, 17% GC, 25% SH 25.8* 34.7*

Stone (1996) 8 M Ct: 26% AS, 26% CS, 23% HMC 20.7 40.7 T: 12% AS, 26% CS, 19% HMC, 14% SH 23.9* 45.9*

Stone (1996) 8 P Ct: 26% AS, 26% CS, 23% HMC 16.6 31.5 T: 12% AS, 26% CS, 19% HMC, 14% SH 18.6* 34.1

1 Not reported or determined; M = multiparous, P = primiparous.2 AH = alfalfa hay, AS = alfalfa silage, CaS = Ca salts of palm fatty acids, CM = concentrate mix, CS = corn silage, Ct = Control, GC

= high-moisture corn, MH = mixed hay, NaB = Na bicarbonate, O = oats, RSB = roasted soybeans, SH = soyhulls, T = treatment. Protein, mare not included.

3Concentrate and SH were fed as a mixture and to ad libitum intake. Hay was offered in restricted amounts. Dietary treatments reported are the actucomposition of the experimental rations consumed by dairy cows.

4Concentrate and SH were fed as a mixture and to supply 454 g of CM/1.4 kg of FCM produced. Forages were fed ad libitum. Dietary treatments reporteingredient composition of the experimental rations consumed by dairy cows.

*Signicant effect ( P < 0.05).Signicant effect ( P < 0.10).LSignicant linear effect ( P < 0.05).I

Signicant linear effect ( P

0.05). For DMI, these results might be expected consid-ering that in 13 of 15 studies no signicant differenceswere detected between the control diets and those con-taining SH (Table 3). In one study, replacing 14% of theDMI supplied as high-moisture corn with SH increasedDMI of multiparous cows ( 2 kg/d), but did not affectDMI of primiparous cows (Stone, 1996). Stone (1996)suggested that higher-than-recommended dietary lev-els of starch in the control diet led to subclinical acido-sissubsequently depressing DMI. However, thestarch content of the control and experimental dietswas not reported. Conversely, when SH were gradually

increased in the diet of lactating dairy cows to replace0, 10, 20, 30, and 40% of the DM supplied as corn, DMIdecreased ( P < 0.06) linearly, but the larger decrease(1 kg/d) occurred when SH supplied more than 30%of the dietary DM (Ipharraguerre et al., 2002a). Basedon data of Batajoo and Shaver (1994), Harmison et al.(1997), Mertens (1997), andIpharraguerre et al. (2002a,2002b), it appears that including > 30% of dietary DMas SH in high grain diets ( 50%) that have a shortageof physically effective ber may elevate the concentra-


Figure 1 . The relationship between DMI (kg/d) and the amountof dietary NDF supplied from SH (% of dietary DM). Data pointscorrespondto data from differentstudies (Macgregor andOwen,1976;Nakamura and Owen, 1989; Bernard and McNeill, 1991; Cunning-ham et al., 1993; Manseld and Stern, 1994; Pantoja et al., 1994;Elliott et al., 1995; Stone, 1996; Ipharraguerre et al., 2002a, 2002b).

tion of acids in the rumen and decrease DMI of cows.However, the lack of sufcient data from experimentsin which SH supplied more than 30% of the dietary DMlimits this analysis.

The NDF content of the experimental diets (Table 3)increased as SH were increased in thediet (NDF rangedfrom 27 to 58%). It is well known that the dietary con-centration of NDF and DMI are inversely and strongly

correlated (Hoover, 1986; Mertens, 1994; Armentanoand Pereira, 1997). Diets that contain more than about32% NDF can limit DMI of cows producing approxi-mately 40 kg/d of milk (Mertens, 1994). Considerablymore dietary NDF ( 44%) is required to restrict DMIof cows producing 20 kg/d of milk. Although the NDFcontent of several diets in which corn was replacedwith SH was similar to or higher than those limits, norelationship between DMI and dietary NDF concentra-tion from SH was evident from the regression and corre-lation ( P = 0.33) analyses (Figure 1). Likewise, Armen-tano and Pereira (1997) pooled data from 32 studiesand indicated that the correlation between DMI and

the NDF content of diets from nonforage ber sourceswas not signicant. An explanation for the apparentdiscrepancy between the effects of forage and nonforageNDF on DMI may be the dissimilar chemical and physi-cal nature of the NDF of forages and SH. First, thereis a clear inverse relationship between DMI and dietaryNDF concentration from studies in which forages werethe major ( 0.58 [Hoover, 1986]) or the sole ( 0.31 [Ar-mentano and Pereira, 1997]) source of NDF. Second,SH contain a pool of potentially degradable NDF that


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is larger than that of most forages used in those studies(e.g., alfalfa silage, corn silage, and alfalfa hay or hay-lage [Sarwar et al., 1991; Pantoja et al., 1994]). In addi-tion, as discussed previously, NDF from SH can be de-graded extensively in the rumen at rates similar to orgreater than that of NDF in forages (Firkins, 1997;Table 2). Third, SH have a small particle size and highspecic gravity that, compared with forages, could dou-ble the passage rate from the rumen (Nakamura andOwen, 1989). Therefore, NDF from SH may not affectDMI to the same extent that NDF from forages doesbecause of differences in their digestion kinetics andphysical bulk.

The linear correlation between milk yield and thepercentage of SH in the diet from the 10 trials thatwere pooled was low ( 0.12) and nonsignicant ( P =0.51). This relationship would be anticipated becauseonly minor changes in milk production have been re-ported when SH either partially or totally replaced ce-real grain in the diet (Table 3). Furthermore, the mech-anism by which SH improved milk yield when theyreplaced grain (Conrad and Hibbs, 1961; Sarwar et al.,1992) could not be identied. For example, Sarwar etal. (1992) reported a linear increase in milk yield of early lactation cows after replacing either 19 or 34% of the DMI supplied as corn with SH. However, roastedSB and inert fats also were added to the SH diets (Table3); therefore, the effect on milk yield was confoundedwith the higher fat content of the experimental rationsin relation to that of the control ration. Only one study(Nakamura and Owen, 1989) reported a signicant de-

crease in milk yield when SH replaced corn in the diet(Table 3). In that trial, Nakamura and Owen (1989)observed that the complete replacement of corn withSH (48% of dietary DM) in diets containing 50% forageand 50% concentrate decreased milk production byabout 2.5 kg/d (Table 3). They suggested that the lowstarch content of the diet that contained SH limitedmilk yield, but the lower DM digestibility of the experi-mental ration (61.3 vs. 69.9% for control) may have alsocontributed, at least in part, to reduce milk production.Unfortunately, the paucity of data from experiments inwhich SH supplied more than 25 to 30% of the dietaryDM restricts this analysis, as well as any attempt to

establish the maximal substitution of SH for corn.Milk fat content from the 10 pooled trials was notcorrelated with the concentration of SH in the diet orthe dietary NDF from SH. The same lack of correlationbetween milk fat concentration and those variables wasevident after removing the variation due to unequalreplications and unequal variation of the means acrossstudies (Figure 2).

Data indicate that the NDF from SH is effective formaintaining or slightly increasing milk fat percentage


Figure 2 . The relationship between the weighted content of fatin milk and the amount of dietary NDF supplied from SH (% of dietary DM). Data points correspond to data from different studies(Macgregor and Owen, 1976; Nakamura and Owen, 1989; Bernardand McNeill, 1991; Cunningham et al., 1993; Pantoja et al., 1994;Elliott et al., 1995; Stone, 1996; Ipharraguerre et al., 2002a, 2002b).

when SH are used to replace grain consumed by cows.In effect, in the studies summarized in Table 3 thedifference between the control diets and those con-taining SH averaged + 0.11 percentage units, and onlyin four trials were differences among treatments sig-nicant (Nakamura and Owen, 1989; Pantoja et al.,1994; Elliott et al., 1995; Ipharraguerre et al., 2002a).In three of those studies, however, the replacement of

18 (Elliott et al., 1995), 20 (Pantoja et al., 1994), or45% of the dietary DM (Nakamura and Owen, 1989)supplied as corn with SH actually reestablished milkfat content to levels near the average of the breeds(Holstein and Jersey) used in the experiments (Table3). In addition, the enhanced concentration of fat in themilk of cows fed diets in which increasing amounts of SH replaced corn grain could not be clearly linked toan additiveeffect of SH on milk fat percentage (Ipharra-guerre et al., 2002a).

The lack of consistent effects of dietary SH on milkyield and milk fat in the trials that were included inthis analysis resulted in a nonsignicant correlation

between the amount of SH used to replace corn and theproduction of FCM. Only one study (Sarwar et al., 1992)reported a linear increase in FCM yield when theamount of SH that replaced corn increased from 19 to34% of the dietary DM (Table 3); however, that effectwas confounded by the addition of fat to the SH diets.In two of the four studies where SH improved milk fatcontent (Nakamura and Owen, 1989; Pantoja et al.,1994), milk production decreased and yield of FCM didnot differ (Table 3).


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Replacing cereal grains with SH signicantly (Fir-kins and Eastridge, 1992; Sarwaret al.,1992; Manseldand Stern, 1994; Pantoja et al., 1994) or numerically(Conrad and Hibbs, 1961; Macgregor and Owen, 1976;Bernard and McNeill, 1991; Elliott et al., 1995; Ipharra-guerre et al., 2002a) depressed the protein content of milk (Table 3). The depression of milk protein concen-tration ranged from 0.8 to 8% when SH provided from18 to 48% of the dietary DM, respectively. This responsemay arise partially because of the low content of NSCin diets that contained high levels of SH, which in turnmay limit microbial protein synthesis in the rumen(Sarwar et al., 1992). Nonetheless, Manseld and Stern(1994) reported that even though the complete replace-ment of corn with SH (30% of dietary DM) reduceddietary NSC from 33 to 23%, microbial populations inthe rumen, microbial N ow to small intestine, andefciency of microbial protein synthesis were not differ-ent. However, milk protein percentage tended ( P < 0.09)to be depressed and milk protein yield was depressedby the SH diet. More recently, the replacement of in-creasing amounts of corn grain with SH to supply 0,10, 20, 30, or 40% of the dietary DM reduced the per-centage of dietary NSC from almost 36 to about 16 andalso did not affect the synthesis of microbial protein inthe rumen of lactating dairy cows (Ipharraguerre et al.,2002b). These data indicate that when SH replace cornto supply 30 to 40% of the dietary DM, changes in theruminal synthesis of microbial protein are not likely tooccur but there might be a reduction in milk proteinoutput.

Based on the higher intestinal availability of NSC incows fed corn versus SH, Manseld and Stern (1994)suggested that more glucose for milk synthesis wasavailable when cows consumed corn. Elliott et al (1995),however, found that the plasma concentration of glu-cose tended ( P < 0.06) to increase when cows receiveddiets in which ground corn was replaced with SH tosupply 18% of the dietary DM. They hypothesized that,although the addition of SH to the diet reduced themolar proportion of propionate, the ruminal concentra-tion of total VFA was enhanced (Table 4); therefore,propionate production and glucose synthesis may haveincreased if total ruminal VFA production increased.

Even though similar shifts in the molar proportion of ruminal VFA were observed, the plasma concentrationof glucose in dairy heifers was not affected by the com-plete replacement of corn with SH, which accounted for30 and 60% of total dietary DM (Nosbush et al., 1996).

Any increase in milk protein output due to higherenergy availability requires an adequate supply of AAto support milk protein synthesis in the mammarygland (Reynolds et al., 1997). Only three studies (Cun-ningham et al., 1993; Manseld and Stern, 1994; Iphar-


raguerre et al., 2002b) have measured the AA ows tothe small intestine of dairy cows fed diets in which SHreplaced corn. In the Manseld and Stern (1994) trial,feeding SH diets decreased Met as a percentage of thetotal proportion essential AA reaching the small intes-tine below that indicated by Schwab et al. (1992) foroptimal AA utilization by mid-lactation cows. Likewise,Cunningham et al. (1993) reported a linear decline inthe total amount of Met delivered to the small intestineas SH increased from 12 to 25% of the dietary DM,but the proportion of Met in total essential AA in theduodenum was about 4.0% for all diets. Differenceswere attributed to the lower Met content of SH in rela-tion to corn (Cunningham et al., 1993; Manseld andStern, 1994) and to the numerically larger DMI of cowsconsuming the control diet (Manseld and Stern, 1994).In contrast, replacing up to 40% of the dietary DMprovided as corn with SH did not alter the passage of

Met to the duodenum of dairy cows (Ipharraguerre etal., 2002b). These few studies suggest that from earlyto mid-lactation, diets in which more than 25% of thedietary DM from corn grain is replaced with SH mightreduce the output of milk protein by limiting the intakeof NSC, the supply of Met to the small intestine, orboth. Conversely, it appears that from mid- to late lacta-tion large amounts of dietary SH can be supplied with-out negatively affecting the concentration of protein inmilk; however, the optimum level is unclear.

Replacing Forage with SH

Although the rst evaluations of SH as an alternativefeed for lactating dairy cows was conducted during theearly 1960s (Conrad and Hibbs, 1961; Wagner et al.,1965), the assessment of their ability to replace foragesin diets of dairy cattle started almost 30 years later(Table 3). With the exception of two studies (Weidnerand Grant, 1994a, 1994b), control diets that contained 50% of the dietary DM as forage were used to deter-mine the potential reduction of negative associative ef-fects of NSC on ruminal digestion of ber when SHreplaced forages. The amount of SH that replaced for-ages ranged from 5 to 25% of total dietary DM, and the

grain was supplied as ground or high-moisture corn.The forages replaced with SH were alfalfa (hay or si-lage), corn silage, or a portion of both. Even though theNDF content of the control (29 to 35%) and SH rations(31 to 37%) was similar among treatments across stud-ies, NDF from forages ranged from about 71 to 86% forthe control diets and from 40 to 60% for the SH diets.In two experiments (Sarwar et al., 1992; Weidner andGrant, 1994b), the proportion of NDF from roughagewas 60% regardless of the dietary level of SH (9 to 15%),


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which suggests that caution should be taken when com-paring results from different reports.

On average, replacing forage with SH increased DMI0.3 kg/d, milk yield 0.7 kg/d, and FCM production 0.4kg/d (Table 3). However, if data are grouped by theNDF concentration from forage for the SH diets andby the forage content of the control diets (DM basis)contrasting inferences can be drawn. First, includingSH in diets that contained 60 to 70% NDF from foragedid not affect DMI or milk yield regardless of the foragecontent in the control diet. For instance, Firkins andEastridge (1992) reported no treatment effects on DMIand milk production when feeding control and treat-ment diets formulated to contain 62.5% NDF from for-age. Eleven percent of the DM in the control diet sup-plied as corn silage was replaced with 7% SH and 4%ground corn on a DM basis to form the SH diets. Simi-larly, performance of cows was not affected when anequal mix of corn silage and alfalfa silage was replacedwith about 15% SH in diets that contained 60% forage(control), which reduced NDF from forage from 86 to60% of total dietary NDF (Weidner and Grant, 1994b).Second, replacing 11 and 22% of the DM supplied ascorn silage in the control diet (50% forage) with SHdecreased NDF supplied as forage from 76% to 58 and40%, respectively (Cunningham et al., 1993). In thatstudy, as SH increased in the diet, DMI decreased lin-early and milk production declined numerically by 2kg/d per cow (Table 3). Third, when 45 to 50% of theNDF in SH diets and more than 50% of the DM incontrol diets was supplied as forages, inclusion of SH

signicantly or numerically improved DMI and milkproduction. Indeed, Stone (1996) found that the addi-tion of 14% of the dietary DM as SH to replace alfalfasilage in a control diet that contained 53% forage in-creased DMI and milk production of multiparous Hol-stein cows. In this experiment, forages provided 71 and47% of the dietary NDF in the control and SH diets,respectively. When the same dietary treatments werefed to primiparous dairy cows, the SH diet numericallyincreased DMI and milk yield, but only DMI was sig-nicantly enhanced (Stone, 1996). Likewise, DMI andmilk production were greater when SH (25%) and al-falfa hay (20%) replaced corn silage (23%) and when

alfalfa haylage (23%) and forages supplied 46% of thetotal dietary NDF, compared with the control diet thatcontained 60% forage and supplied 62% of the NDFfrom forage (Weidner and Grant, 1994b).

In general, there was little change in milk composi-tion when cows were fed diets in which SH partiallyreplaced forages (Table 3). Milk protein concentrationwas increased in one trial (Stone, 1996) and decreasedin another (Weidner and Grant, 1994b), but reasonsfor these changes were not given. As highlighted by


Titgemeyer (2000), two studies (Pantoja et al., 1994;Weidner and Grant, 1994b) reported opposite responsesfor milk fat percentage in spite of the similar amountof SH and type of forage fed to the cows. Weidner andGrant (1994b) observed that replacing 15 and 25% of the DM supplied as a 1:1 (wt/wt) silage mixture (alfalfaand corn) with SH in a diet that contained 60% foragedecreased milk fat content (8 and 10%, respectively).On the other hand, for diets containing 60% forage, thereplacement of 8 and 12% of the total DM from alfalfasilage and corn silage with SH (20% of dietary DM)enhanced milk fat concentration by about 15% (Pantojaet al., 1994). In those studies, the contrasting milk fatpercentages were positively correlated with oppositechanges in the ruminal acetate-to-propionate ratio (Ta-ble 4). Interestingly, in the study of Weidner and Grant(1994b) when a portion of the silage mixture was re-placed with 20% alfalfa hay (coarsely chopped) in the

SH diets, the replacement of the silages with SH in-creased milk fat percentage (Table 3). They reportedthat the inclusion of SH decreased the mean particlesize of all diets, but less so when long alfalfa hay wasadded. Furthermore, as dietary SH were increased, to-tal chewing time declined, but the decrease was par-tially or totally prevented by the addition of coarse hay.Thus, the SH diets used by Weidner and Grant (1994b)and Pantoja et al. (1994) may have presented differentphysical effectiveness for stimulating rumination andsalivation, resulting in opposite changes in ruminal fer-mentation and milk fat percentage. Stone (1996) re-placed 14% of the dietary DM supplied as alfalfa hay-lage with SH in a diet that contained 53% forage andestimated that the effectiveness of NDF in SH was 53%of that in alfalfa ber for promoting rumination. Feed-ing diets with as little as 34% forage (mixture of alfalfaand corn silages) and as much as 23% SH also failedto sustain total chewing activity per unit of NDF con-sumed (i.e., time spent eating and ruminating per kgof NDF intake; Slater et al., 2000). However, milk fatpercentage was depressed only when ruminally degrad-able starch was increased by the partial replacementof corn (8%) with wheat (12%). Diets that containedonly 23% forages, almost 31% SH, and about 27% cereal

grain, which was supplied as corn or as mixture of corn (55%) and wheat (45%), did not affect milk fatconcentration or milk production of Jersey cows duringearly lactation (Harmison et al., 1997). In both studies(Harmison et al., 1997; Slater et al., 2000), the lackof a milk fat response coincided with similar ruminalacetate-to-propionate ratios for the control and SH diet.Even though the physical effectiveness of the diet (mea-sured as stimulation of chewing) decreased as SH re-placed forage, the potential benets on ruminal fermen-


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tation (chemical effectiveness) of NSC dilution withSH may prevent milk fat depression.

These data suggest that SH might be used to replaceforages in dairy diets when the supply of effective ber,which includes a chemical and a physical component,remains adequate after including SH. In cases whereforages constitute 50% or less of total dietary DM orhave small particle size, their replacement with SHmay depress dairy cow performance as a result of aninadequate supply of effective ber. On the other hand,in situations where forages represent 50% or more of dietary DM and have a particle size that guaranteesadequate physical effectiveness, the substitution of SHfor forages may not affect or may improve the perfor-mance of dairy cows. Furthermore, SH may enhancemilk fat percentage because of the replacement of NSCor starch rather than from the stimulation of chewingactivity. Therefore, the source, amount, and physicalform of forages largely affect the use of SH in dairydiets (Grant, 1997).

RUMINAL FERMENTATION CHARACTERISTICS

The inclusion of SH in dairy diets has resulted in aruminal fermentation pattern that has either main-tained or enhanced the ruminal concentration of total VFA (Table 4). That response has consistently beenobserved in a number of studies in which different di-etary forage-to-concentrate ratios were used or evenwhen forages or grains were replaced with SH. Forinstance, when Cunningham et al. (1993) added 12 or25% of thedietary DM as SH to replace similar amountsof either corn silage or high-moisture corn, the concen-tration of VFA in ruminal uid increased for the SHdiets even though the NFC concentration of these dietswas lower (Table 4). Based on similar ndings, Mans-eld and Stern (1994), Pantoja et al. (1994), and Sarwaret al. (1992) proposed that the high content of fer-mentable NDF present in SH might allow a more exten-sive ruminal fermentation, possibly resulting in higher VFA concentrations. In fact, the in situ rate and extentof degradation of NDF in SH remained high under awide range of dietary conditions (Table 2). Further-more, the amount of dietary NDF apparently digested

in the rumen of lactating dairy cows either increased(Pantoja et al., 1994) or did not change (Cunninghamet al., 1993) when SH were substituted for forages butconsistently increased when SH replaced corn (Cun-ningham et al., 1993; Manseld and Stern, 1994; Iphar-raguerre et al., 2002b).

In contrast, the replacement of either forages orgrains with SH has resulted in dissimilar shifts in themolar proportion of individual VFA, pH, and NH 3Nconcentration of ruminal uid (Table 4). Substitution


of SH for corn, which ranged from 12 to 40% of thedietary DM, diminished the molar proportion of propio-nate and butyrate and enhanced that of acetate (Table4). Consequently, feeding diets that contained SH hasconstantly increased the ruminal acetate-to-propionateratio. Moreover, in all experiments that ratio reached values of 2.5:1, which is greater than the minimumrequired to sustain normal milk fat percentages (Erd-man, 1988). Nonetheless, the molar proportion of totallipogenic VFA (i.e., acetate and butyrate) in ruminaluid slightly increased or remained unaffected, whichmay explain, at least in part, the lack of changes inmilk fat content observed in most of those studies.Manseld and Stern (1994) concluded that the above-described changes in the molar proportion of VFA inruminal uid revealed a shift from fermentation of NSCto ber in the rumen. They noted that the replacementof 30% of dietary corn with SH decreased the amount

of NSC apparently digested in the rumen by 21% andincreased that of NDF by 48%.Despite the shift in ruminal fermentation, feeding

SH in place of grains to ruminants usually failed toaffect the pH of the ruminal uid (Table 4). Sarwar etal. (1992) indicated that replacing 19 and 34% of thetotal dietary DM supplied as ground corn with SH inhigh grain diets attenuated the characteristic postfeed-ing decline of ruminal pH, but that improvement wasonly signicant at 9 h postfeeding. In addition, mostreports (Highll et al., 1987; Anderson et al., 1988;Galloway et al.,1993; Manseld andStern, 1994; Elliottet al., 1995) indicate that feeding SH in place of grainsresulted in an average ruminal pH ( 6.0) that appearsto be adequate to support ruminal microora and cellu-lolysis (Mould et al., 1983; Mould and Orskov, 1983;Hoover, 1986; Grant and Weidner, 1992).

Replacing forage with SH in dairy diets to supplyfrom 5 to 25% of dietary DM usually increased themolarproportion of propionate in ruminal uid (Table 4), butalterations in molar percentages of acetate and buty-rate were infrequent or inconsistent. In part, these re-sults may have arisen from differences in the amountof forages fed in those experiments. The addition of SHto replace forages in diets that contained more than

50% forage did not affect the molar proportion of acetateand butyrate (Weidner and Grant, 1994a, 1994b; Stone,1996). Conversely, when forages provided less than 50%of total dietary DM, the inclusion of SH in the dietsignicantly decreased the molar proportion of acetate(Sarwar et al., 1991, 1992) and butyrate (Sarwar etal., 1992; Cunningham et al., 1993). Hsu et al. (1987)suggested that the highly fermentable ber of SH mightlead to a concentrate-type ruminal fermentation pat-tern when SH are used to replace forages. That effect


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14/22


T a

b l e 4 ( c o n t i n u e

d ) . R u m i n a l f e r m e n t a t i o n c h a r a c t e r i s t i c s o f l a c t a t i n g d a i r y c o w s f e d d i e t s i n w h i c h s o y h u l l s r e p l a c e d c e r e a l g r a i n s o r f o r a g e s .

S t u d y

D i e t a r y t r e a t m e n t s

1

p H

N H

3 N

2

V F A

A c 3

P r 4

B u 5

A c : P r 6

S o y h u l l s r e p l a c e d g r a i n s

( m g / d l )

( m

M / L )

( m o l / 1 0 0 m o l

)

S t o n e

( 1 9 9 6 )

C t : 2 6 % A S

, 2 6 % C S

, 2 3 % H M C

N R

N R

N R

6 4 . 3

2 0 . 6

1 1 . 2

N R

T : 1 2 % A S

, 2 6 % C S

, 1 9 % H M C

, 1 4 % S H

N R

N R

N R

6 3 . 5

2 2 . 0

1 0 . 8

N R

1 A H

=

a l f a l f a h a y , A S

=

a l f a l f a s i l a g e ,

C a S =

C a s a l t s o f p a l m f a t t y a c i d s , C S

=

c o r n s i l a g e ,

C t

=

c o n t r o l ,

G C

=

g r o u n d c o r n ,

G H

=

g r a s s h a y , H M C

=

h i g h - m o i s t u r e c o r n ,

R S B

=

r o a s t e d s o y b e a n s , S H

=

s o y h u l l s , T

=

t r e a t m e n t . P r o t e i n

, m i n e r a l ,

a n d v i t a m i n s u p p l e m e n t s a r e n o t i n c l u d e d .

2 N H

3 N

=

A m m o n i a n i t r o g e n .

3 A c e t a t e

.

4 P r o p i o n a t e .

5 B u t y r a t e

.

6 A c e t a t e - t o - p r o p i o n a t e r a t i o

.

7 N o t r e p o r t e d o r d e t e r m i n e d

.

* S i g n i c a n t e f f e c t

( P

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Soyhulls as an Alternative Feed for Lactating

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