Milk Production Characteristics and Productivity of N'Dama Cattle KeptUnder Village Management In The Gambia

K. AGYEMANG1Intemational Uvestock Centre for AfrIca

ethiopia

R. H. DWINGER, A. S. GRIEVE, and M. L. BAHInternational Trypanotolerance centre

P.M.B. 14BanjUl, The Gambia

ABSTRACT

Our objective was to quantify the milkproduction of N'Dama cattle kept undervillage conditions as part of an epidemio­logical study designed to identify produc­tion constraints and to develop strategiesto improve livestock productivity offanners with small holdings. Milk andcomponent yields were monitoredmonthly by measurement of milk ex­tracted for human use (milk offtake) plusthat consumed by the calf, estimated frombody weight changes. Least squaresanalyses of 668 lactations recorded over 4yr gave mean lactation length, 420 d;milk offtake, 404.3 kg; fat, 5.1%; protein,3.2%; calf weaning weight, 88.1 kg; andcalving interval, 641 d. A productivityindex incorporating milk offtake, calfweaning weight, calving rate, and viabil­ity gave a mean annual 140.6 kg ofweaner calf plus the weight equivalent ofmilk offtake per 100 kg of cow metabolicweight. The index was higher than thatrecorded for larger Zebu (Bos indicus)cattle managed under similar productionsystems elsewhere in Africa. Theseresults show that the trypanotolerantN'Dama cattle appear to be more produc­tive than previously thought and shouldtherefore be considered when promotinglivestock development in Africa, espe­cially in tsetse-infested areas where otherbreeds cannot survive.

Received March 1, 1990.Accepted July 25, 1990.lIntemational Trypanotolcrance Centre, PMB 14 Ban­

jul, The Gambia. Author to whom reprint requests shouldbe addressed.

(Key words: N'Dama cattle, milk, yield)

Abbreviation key: Ix =once daily, 2x =twicedaily.

INTRODUCTION

Approximately 10 million km2 of Africa'shumid and subhumid region is infested withtsetse flies, and the trypanosomes they transmitcause trypanosomiasis in humans and livestock.These tsetse-infested areas, which also includesome of the best watered and fertile lands ofthe region, are thus rendered largely unsuitablefor livestock farming. It has been argued that alarge part of these infested areas could be put toimmediate use for livestock or mixed agricul­tural development if trypanosomiasis could becontrolled. Previous efforts to rid the areas oftrypanosomiasis have included tsetse control bythe use of insecticides, clearing of large areasof tsetse habitat, and use of trypanocidal drugsto treat infected livestock. These approaches arebecoming increasingly less attractive in manysituations because of high failure rates, highcost, or concerns for environmental pollution ordegradation.

Another approach that has generated muchinterest recently is the use of trypanotolerantlivestock in these tsetse-infested areas.Trypanotolerant livestock are known to surviveand maintain reasonable production in spite ofthe presence of tsetse and trypanosomes (10).In order to gain a better understanding of thefactors that influence the trypanotolerant trait,the International Trypanotolerance Centre wasset up in The Gambia. At the Centre, multidis­ciplinary teams of scientists have been investi­gating the productivity of trypanotolerant live­stock, in particular, N'Dama cattle.

The N'Dama has been and currently is usedin several traditional production systems as amultipurpose breed providing milk, meat, ma-

1991 I Dairy Sci 74:1599-1608 1599

1600 AGYEMANG ET AL.

nure, and traction. Much of the production dataon N'Dama has been collected at governmentor university research stations at which almostinvariably only meat production characteristicswere studied. Therefore, information is notavailable on milking characteristics and, hence,productivity of the breed in tenns of meat andmilk under traditional management systems. Aspart of a large-scale epidemiological study toestimate the productivity of N'Dama cattle 00­

der different degrees of tsetse challenge, a milkrecording scheme was initiated in selected vil­lages in The Gambia. The objective of thispaper is to report on milk production character­istics and the contribution of milk extracted forhuman consumption to the overall productivityof the breed.

MATERIALS AND METHODS

The Study Area

The studies were carried out in four villagesin the Republic of The Gambia, latitude 13·05'to 13·5O'N and longitude 13·47' to 16·5O'W.The climate is Sudano-Guinean with mean an­nual rainfall of 800 to 1000 nun, decreasingfrom coastal to inland areas. Mean annual rain­fall recorded for 1987 and 1988 in each of thefour villages were for Gunjur, Pirang, Keneba.and Nioro Jattaba 1383, 1540, 1074, and 1509mm, respectively. Tsetse challenge in theseareas varies. Gunjur and Nioro Jattaba are clas­sified as low challenge areas and Keneba andPirang are low to seasonally medium. Thisclassification was based on tsetse fly catchesand trypanosome infection rates in flies (W. F.Snow, personal communication) and cattle inthese villages.

Herd Management

N'Dama are descendants of taurine Hamiticlonghorns, which arrived in the Nile Delta fromthe Near East some 7000 yr ago (6, 17). Underthe village management systems in The Gam­bia, animals are tethered overnight on groundsclose to the homestead. Breeding is open withone or more bulls running with the herdthroughout the year. Calvings occur throughoutthe year, but more than 80% occur from July toDecember with peak calving occurring in Au­gust and September (11). Extraction of milk for

lomnal of Dairy Science Vol. 74, No.5, 1991

human use begins 1 to 2 wk after calving.Milking is done once daily (Ix) in Nioro Jat­taba and twice daily (2x) in Gunjur, Pirang, andKeneba. Morning milking starts at approxi­mately 0600 h and evening milking between1800 and 2200 h, depending on the season ofthe year. Cows are hand-milked with the calf atfoot. Milk ejection is initiated by pennitting thedam to suckle the calf briefly. The cow ispartially milked with some residual milk leftfor the calf.

FIeld RecordIng and LaboratoryAnalytical Procedures

Approximate year of birth was assigned toeach animal at the time of initial identificationbased on dentition and breeding history pro­vided by herd owners and herds persons. Theassigned year of birth was incorporated into theidentification number. For breeding females,the number of calves produced by the time ofinitial registration was recorded. Animals sub­sequently born or bought into the herds wereear-tagged by veterinary or milk recording as­sistants based in the villages. Quantities of milkextracted for human use (milk offtake) over andabove that consumed by the calf was measuredin a calibrated cylinder for individual cowsduring evening and the subsequent momingmilkings, once a month at an interval of 25 to35 d. Milk recording started 1 to 2 wk aftercalving. A 2Q-ml sample from the momingmilking was collected to determine fat percent­age using the Gerber method and protein per­centage using a formaldehyde titration method.Milk fat and protein testing were started 8 and12 mo after milk recording began. Therefore,fewer records were available for statisticalanalysis. The cow and suckling calf wereweighed at the time of milk measurement usingportable electronic scales (Barlo, Australia).Animals were also bled every month, and theblood was examined for trypanosomes usingthe dar.k ground method (14). The extent ofparasitaemia was quantified by a scoring sys­tem (16).

Data Preparation andStatlsUcal Analyses

All measurements were stored on microcom­puter files for each cow-calf pair for eachmonth. Evening and morning milk were added

MILK. PRODUCTION OF VILLAGE-RAISED N'DAMA CATILE

TABLE 1. Frequency distribution of milking termination codes for village N'Dama cattle berds.

Termination Number of PercentageCode Reason n::cords of total

1 Normal termination with weaned calf 657 73.22 Dead or lost calf 158 17.73 Protracted sickness of cow 10 1.14 Cow sold 29 3.25 Death of cow 43 4.8

Total 897 100.0

1601

to obtain a daily offtake value. These monthlydaily offtake values were summed to obtain thecwnulative lactation offtake for each cow bythe use of the modified test interval method(28). One liter of milk. was asswned to weigh Ikg. Fat and protein yields from the milk ex­tracted were calculated as the product of the fator protein percentage and the milk offtake. Atotal of 897 completed or terminated lactationsfrom cows were recorded from October 1985 toSeptember 1989. Distribution of the data set byreason of termination of lactation is given inTable 1. Of this total, 116 records were ex­cluded from the data on the grounds of incom­plete blood sampling information. The finaldata set used for analyses was obtained fromrecords meeting one of the following condi­tions: 1) a normally terminated lactation record,2) abruptly terminated lactations that lasted for180 d or more, and 3) abruptly terminatedlactations independent of duration if the damwas found to have been infected with trypano­somes any time during the lactation. Thisresulted in 668 records for analyses of lactationlength and lactation milk. offtake, 531 for fat,333 for protein, 668 for calf birth weight, 582for calf weaning weight, 642 for average post­partum weight of cow, 326 for calving interval,and 348 for productivity indices. Milk offtake,calf weaning weight, average postpartum cowweight, calving interval, and indicators of calfviability were combined to calculate three mea­sures of productivity indices. These indiceswere calculated as index 1 = kilogramsIiveweight of weaner calf produced plusliveweight equivalent of milk offtake for hu­man use per cow maintained per year =[(liveweight of calf at weaning + lactation milkofftake/9) x 365]/subsequent calving interval.The factor of 9 as a divisor of lactation milkofftake is based on reports of Drewry et at. (5)

that showed an additional unit of calf gain forevery 9 units of additional milk. conswned.Calculations based on data of Montsma (13)indicate that for N'Dama cattle this value isabout 8. The divisor 9 was used to allow com­parison with others (Wagenaar et aI. (27»; in­dex 2 = kilograms liveweight of weaner calfproduced plus liveweight equivalent of milkofftake for human use per 100 kg of cowmaintained per year =(index l/average postpar­tum weight of cow) x 100; and index 3 =kilograms liveweight of weaner calf producedplus liveweight equivalent of milk offtake forhuman use per 100 kg of metabolic weight ofcow maintained per year =(index l/cow aver­age postpartum weight .73) x 100. Becausesubsequent calving interval is needed for cal­culating productivity indices, only cows withmultiple parturitions were considered; and be­cause most cows calve every other year (11),for the present purpose, calvings initiated afterJune 1987 were excluded from the analyses.

For cows calving prior to July 1987 (7.6%)and still in the herds but with no subsequentcalving by the time of analysis in October1989, an arbitrary calving interval of 1095 d (3yr) was assigned based on the expectation thatthey would have calved by June 1990. Exclu­sion of such cows from the data would havebiased the mean interval downward In order tocalculate indices for each cow, the followingrules were adopted: indices were set to zero ifthe cow died during or after lactation sincethere was no opportunity to have a subsequentinterval; for cows with calves that died beforeweaning, the liveweight of weaner calf was setto zero, and milk offtake from such cows up tothe time of death of calf was the sole portion ofproduction considered The inclusion of recordsof cows that died and zero weights for deadcalves accounted for cow and calf mortality in

Journal of Dairy Science Vol. 74, No. S, 1991

1602 AGYEMANG ET AL.

TABLE 2. Unadjusted means, standard deviations. 8Dd range for production parameters.

Parameters

Lactation length, dMilk offtake, kgFat percentage, %Protein percentage, %Fat yield, kgProtein yield, kgCalf birth weight, kgCalf weaning weight, kgAvg. postpartum cow weight, kgCalving intel'Val, dProductivity index I, kgProductivity index 2, kgProductivity index 3, kg

Number ofrecords

668668531333531333668582642326348348348

Mean

420404.3

5.13.2

18.811.617.588.1

225.764173.532.6

140.6

SD

138.6183.1

1.0.3

10.55.92.7

27.328.2

200.833.714.462.2

Range

7G-I0182~1071

2~7.9

2.3-4.1l.l-<iO.8.5-33.3

8-2426-20314~329

31~1069

G-153.0G-64.2G-269.7

the indices. All analyses were carried out byusing least squares procedures (8). The generalmodel assumed was

Y=XB+e

where Y is a vector of observations of thedependent variables listed in Table 2, X is aknown fixed design matrix for the trait lDlderconsideration, B is an unknown vector of fixedeffects, and e is an lDlobservable vector ofrandom errors, identically and independentlydistributed with mean zero and variance-covari-

ance matrix Ia;. The fixed effects included the

following factors: system of milking manage-­ment (lx, 2x milking), parity of cow (first, twoto four combined, and all parities greater thanfour combined), trypanosome infection status incow during lactation (uninfected, infected), sexof suckling calf (male, female), year-season ofcalving [1985, 1986, 1987, 1988 in combina­tion with wet season (July through October)and dry season (November through June)], andherd nested within system of milking (8 in Ixand 16 in 2x milking systems). Herds withinthe 2x milking system were situated in threelocalities, two of them near the coast and thethird further inland A statistically significanteffect due to herds could reflect the differencesin annual amOlDlts of precipitation and hencefeed resources in these localities. Large differ­ences among herds in a given locality couldindicate differences in herd management suchas choice of grazing sites, frequency of water-

Journal of Dairy Science VoL 74, No.5, 1991

ing animals, and changing of holding groundsto avoid build up of intemal parasites. Similarlyfor herds within the Ix system, all of whichwere situated in one locality, a statisticallysignificant difference could be ascribed to herdmanagement.

Interaction effects were dropped from themodel as preliminary analyses indicated non­significance (P > .60). The identities of servicesires were not known; therefore, sire effectswere not considered in the analyses.

Least squares means for each value of aneffect were obtained from solutions to the leastsquares equations. These means are individu­ally adjusted for other effects in the model;hence, they may differ from the raw or unad­justed means.

Repeatabilities were estimated from intra­cow correlations using the mixed model

Y = XB + Zu = e,

where Y is a vector of observations for thetraits listed in Table 2 where adequate numbersof cows with multiple measurements existed, Xis a known fixed design matrix, B is a knowndesign matrix representing herd, year-season,and parity of cow, Z is a known design matrix,u is an lDlobservable vector of random coweffects nested within herds with mean zero andvariance-covariance matrix I~, and e is anunobservable random vector of errors with a

mean zero and variance-covariance matrix Ia;.

Variance components for cows and errors were

MILK. PRODUCTION OF VILLAGE-RAISED N'DAMA CATILE 1603

calculated, and repeatability was computed as

~(~ ~) with estimates obtained from

mixed model options of Harvey's least squaresprogram (8).

RESULTS AND DISCUSSION

Published work on long-term studies ofN'Dama production in traditional systems andon milk offtake in particular in villages isscarce. The few reports available on milk pro­duction were carried out at research stations (9,13) over short periods of lactation, and milkcomposition was not included. Therefore, com­parison of results with others under similarmanagement conditions is not possible. Whereapplicable, results obtained on herds maintainedat research stations will be used to highlight thedifferences between station and village produc­tion systems, and to demonstrate the trade-offsbetween milk and beef production. Similarly,productivities of Zebu cattle will be discussedto compare trypanotolerant N'Dama andtrypanosensitive cattle kept under similar man­agement systems. Frequencies, means, standarddeviation, and ranges of the traits studied are inTable 2. About 18% of all lactations wereterminated due to the death or disappearance ofsuckling calves. The most common cause ofcalf mortality was black leg (clostridial infec­tions).

lactation Length and lactationMilk O:ftake

Effect of milking management system wassignificant for lactation length (P < .01) andmilk offtake (P < .001). Cows were milked onaverage 51 d longer in the Ix than in 2xmilking system (Table 3). Despite the shorterlactation length for 2x milking, 66% more milk(158 kg/cow) was extracted than in the Ix(Table 3), which was as expected (18).

Herd effect was significant (P < .001) formilk offtake in 2x milking but not in Ix sys­tem. Ranges in herd milk offtake in the 2xsystem was wider (280 to 539 kg) than in Ix(176 to 301 kg). Among herds in a givenlocality there was a tendency for smaller herdsto extract more milk per cow per day of lacta­tion. Year-season of calving effect was signifi­cant (P < .001) for both Iactation length andmilk. offtake, mainly due to shorter lactation

length associated with lactations initiated in1988. Cows with longer lactations were still inmilk and were not included in the analyses.Within years, except for 1988, cows that calvedin the wet season tended to have a higher milkofftake and longer lactation length than thosecalving in the dry season. Milk offtake per dayof lactation showed little effect of wet and dryseason calvings. The better than expected per­formance of cows calving in the dry seasoncould be explained by the increase (50 to 75%)in daily milk production that occurred 3 to 5mo after dry season calving due to the onset ofrains in July. For cows calving in the wetseason, daily milk offtake declined at a slowerrate, but in this case, the nutritional boost fol­lowing the next rain did not occur until 9 to 12mo postcalving (2). It appears that inadequatenutrition in lactating females is a limiting factorin milk yields under village management. Thepositive effect of feed supplementation to lac­tating cows on milk yield was demonstrated byRiley el at (19).

Parity effect was significant (P < .01) onmilk offtake but not on lactation length; highestmilk offtake was from cows in second to fourthlactations, followed in decreasing order by pri­miparous cows and cows in lactation greaterthan four. The pattern of peak milk productionoccurring in midcareer cows has been foundboth in Bos indicus and Bos taurus in tropicalenvironments (25, 29). Results of lactation milk.offtake of the past were mostly based on fieldobservations or farmer interviews and gave un­adjusted means of 60 to 100 kg for a lactationlength of 1 yr (10, 23).

The mean of 404 kg over a lactation lengthof approximately 14 mo observed in the currentstudy was four to six times previous estimates.The lactation length achieved may be related toherd management and cultural practices gearedtowards maximum milk extraction, but it alsoshows that the short Iactation lengths usuallyassociated with tropical indigenous cattlebreeds may not be a production constraint forthe N'Dama. This observation, coupled withannual milk offtake of 600 kg for individualcows, gives an indication of the potential todevelop the N'Dama as a dual purpose breed.Milk offtake from cows uninfected withtrypanosomes during the lactation period was24 kg more than those infected at least onceduring lactation (Table 3), although the differ-

Jomnal of Dairy Science Vol. 74, No.5, 1991

1604 AGYEMANG ET AL.

TABLE 3. Least squ.area means for milk: offtake and component traits.

Least squ.area means

Lactation Milklellg1h offtake Fat Fat Protein Protein

Factors (n) (d) (kg) (n) (%) (kg) (n) (%) (kg)

Overall mean 668 411 317.5 531 4.9 14.1 333 3.2 8.6System of milkingl

70 3.2 6.2Ix 138 437 238.6 127 4.7 9.52x 530 386 396.4 404 5.2 18.7 263 3.2 10,9Average SE 16.6 19.3 .13 1.2 .OS .8

Parity of cow9.01 204 428 314.7 164 5.0 14.0 110 3.3

2-4 352 414 344.6 277 4.9 15.3 166 3.2 9.2>4 112 393 293.1 90 4.9 13.0 57 3.2 7.6Average SE 16.5 19.1 .12 .12 .OS .9

Infection statusInfected 45 413 305.7 29 5.0 13.8 17 3.3 8.8Unmfected 623 410 329.3 502 4.9 14.4 316 3.1 8.4Average SE 17.1 13.2 .12 1.3 .05 .9

Sex of calfMale 342 416 323.6 267 4.9 14.3 173 3.2 8.2Female 326 4m 311.3 264 4.9 14.0 160 3.2 9.0Average SE 15.2 17.7 .12 1.1 .OS .8

Year-season of calving1985, Wet 13 473 332.61985, Dry 39 444 331.61986, Wet 168 454 393.0 110 5.2 19.21986, Dry 95 434 352.4 68 4.9 17.21987, Wet 176 449 353.1 176 4.8 15.9 176 3.2 10.91987, Dry 118 418 332.9 118 4.7 14.7 98 3.2 10.31988, Wet 18 266 170.0 18 5.2 6.4 18 3.2 4.71988. Dry 41 354 274.2 41 4.7 1l.2 41 3.2 8.4Average SE 23.8 27.6 .16 1.5 .06 1.0

lMillcing occurred ooce (IX) or twice (2x) daily.

ence was not significant (P = .34). Agyemanget al. (l) estimated a larger difference in milkofftake between uninfected and infectedN'Dama cows during the first 6 mo after infec­tion. The smaller difference in milk offtakebetween infected and uninfected observed inthis study could be partly because over anextended lactation period climatic conditionsthat lead to increased feed availability tend toreduce the negative impact of trypanosome in­fections on productivity (1).

Milk Composition

System of milking management, year-seasonof calving, and herd within 2x milking systemall had significant effects (P < .01) on fatpercentage, and the effects of parity and herdwere significant on protein percentage. Fat per­centage recorded for cows milked 2x was .5

Journal of Dairy Science Vol. 74, No.5, 1991

unit (11%) higher than for Ix (Table 3). Cowsthat initiated lactations during the wet seasonproduced about .3 unit (6%) higher percentageof fat than those that initiated lactation in thedry season (Table 3). This difference could beexplained by the fact that a greater proportionof the milk: offtake from cows calving in thedry season is extracted during the subsequentwet season. when the lowest fat concentrationsare observed (2). The mean fat percentage of5.1 was obtained from milk extracted in themorning. The actual milk fat percentage basedon a composite of evening and morning milkcould be even higher as fat percentage fromevening milk is generally higher than that ofthe morning milking (22). It is also thought thatthe portion of the milk consumed by the calfafter milk offtake may be higher in fat percent­age than the estimated value as milk stripping

MILK PRODUCTION OF vnLAGE-RAISED N'DAMA CATILE 1605

has been reported to be high in fat. Because themilk consumed by the calf prior to handmilkingwould be lower in fat percentage than that ofthe residual, fat percentages based on the morn­ing milk should be about average for the N'Da­mao Nevertheless, the mean recorded washigher than for crosses between Friesian andZebu cattle (12) and similar to that of an Flcross between N'Dama and Jersey cattle in atropical environment (20). The mean proteinpercentage of 3.2 was similar to values reportedfor other breeds of cattle. The high fat percent­age of N'Dama cattle, kept under a manage­ment system in which calf nutrition is likely tobe inadequate in the dry season, is desirable forcalf growth.

Milk Component YIelds

Factors that significantly influenced milkofftake also affected fat and protein yields.

L1veweight Traits

System of milking, parity, year-season, sexof calf, and herd within system of milking hadsignificant effects on calf birth weight. Birthweight of calves born in 2x milking system(17.3 kg) was 1.5 kg (10%) heavier than calvesin the Ix milking system. Mean calf birthweight was lowest for primiparous cows.Calves born during the wet season in a givenyear were .3 to 1.0 kg heavier than those bornin the dry season. Males averaged 1.3 kg (8%)heavier than females at birth. Birth weight was1 to 2 kg heavier for herds at the coastal thanthat found in the interior locations. The meanbirth weight of 17.5 kg in the village herds wassimilar to that of N'Dama cattle in station­managed herds (7, 26) and 17% heavier thanthat reported by Carew et al. (4) for a stationherd in Sierra Leone.

Weaning weight was influenced by systemof milking and year-season of birth (P < .001),sex of calf (P < .05), and herds. Weaningweight was 22 kg (29%) heavier in the Ix thanin the 2x milking system. Year-season effectswere mainly due to lighter weaning weightsassociated with shorter weaning period forcalvings initiated in 1988. Male calves wereweaned at a heavier weight than females (88.7vs. 84.7 kg). Liveweight at 14 mo in this studywas only 75 to 85% of that achieved at 8 to 9mo at research stations in Senegal (7) and inThe Gambia (15).

Effects of system of milking management,parity, and herds on 2x milking were all signif­icant (P < .01) for postpartum cow weight.Cows averaged 9.6 kg heavier in 2x milkingherds. Primiparous cows were lightest, fol­lowed in descending order by cows with two tofour parities and those of parities greater thanfour. Cows tended to be heavier at the coastalthan inland localities. Weight of village cowswas 20% less than that of cows kept at researchstations in The Gambia (15) and in Senegal (7)but 12% heavier than for cattle kept at a stationin Sierra Leone (4).

Calving Interval

The mean calving interval for 301 recordsobtained from cows with last parturition occur­ring before July 1987 was 604 ± 160 d. Theinclusion of 25 cows with intervals projected to1095 gave a longer mean of 641 ± 200 d.Although parity of previous calving was notsignificant on calving interval, the mean inter­val (630 d) for cows with parities greater thanfour was 42 d shorter than for primiparouscows.

Interval for cows in midcareer (parities 2 to4) was intermediate between the primiparousand older cows. This trend agrees with previousreports (25). Effect of previous year-season ofcalving was not significant (P > .05) on calvinginterval. Calving interval for cows infected withtrypanosomes was 56 d longer than for unin­fected cows. Interval for cows suckling malecalves was 27 d longer than for cows withfemale calves. Herd effects on 2x milking wereimportant (P < .05). The mean calving intervalof 641 in this study was longer than valuesrecorded for N'Dama at research stations inSierra Leone (4, 24), Senegal (7), and Ghana(26), but the interval was more similar to the634 recorded at the Yundum station in TheGambia (15). Calving rates ranging from 45 to54% (i.e., intervals of 675 to 800 d) have beenreported for indigenous Zebu breeds under tra­ditional management systems in Africa (27,30). Thus, the long interval in this study maynot be a breed characteristic but is more likelyrelated .to long lactation periods as a positivecorrelation (P < .01) of .69 was obtained be­tween the two traits.

CorrelaUons

Lactation length was moderately correlated(P < .01) with yield traits (.56 to .58), fat

Journal of DaiJy Science Vol. 74, No. S, 1991

1606 AGYEMANG BT AL.

TABLE 4. Least squares means for productivity indicesl

Factors No. Index 1 Index 3

------- (kg) -------

129.7122.4

9.65

124.8127.210.78

120.2131.910.35

131.8125.7120.610.49

126.0

30.228.62.22

29.4

29.129.72.49

31.329.227.72.40

28.330.52.38

60.469.45.66

64.9

64.365.5

5.89

64.465.464.95.n

67.162.75.30

65283

348

27321

174174

9918861

Overall meanSystemof~Ix2xAverage SE

Parity of cow12-4>4Average SE

Infection statusInfectedUninfectedAverage SE

Sex of calfMaleFemaleAverage SE

Year-season of calving1985, Wet 13 71.9 32.9 140.51985, Dry 38 57.8 25.2 109.11986, Wet 166 74.3 33.8 144.81986, Dry 95 67.4 30.0 129.21987, Dry 36 53.2 25.2 106.6Average SE 7.04 2.97 12.89

lBased on a weaner calf (14 mo of age) and Iiveweigbt equivalent of milk offtake for human use.

2Milldng OCCUlTed once (IX) or twice (2x) daily.

percentage (.42), and protein percentage (.29).Milk offtake was highly correlated with fatyield (.94), protein yield (.97), and protein per­centage (.21). These correlations are within therange reported for other breeds.

Productivity Indices

Body weight of a weaned calf (approxi­mately 14 mo) plus the liveweight equivalent ofmilk offtake for human use (index 1) based on348 parturitions was 73.5 ± 33.7 kg. Means forindices 2 and 3 were 32.6 ± 14.4 kg and 140.6± 62.2 kg (Table 2). The slightly more records(348) used for productivity indices than forcalving interval (326) were due to the inclusionin the former case of dead cows with no subse­quent interval to account for cow mortality.Least squares means are given in Table 4.

System of milking effects were not signifi­cant for any index, although the means forindices 1, 2, and 3 in the 2x milking system

were 9.0, 2.2, and 11.6 kg heavier than those inthe Ix system (Table 4). The combined effectsof 60% higher milk offtake in the 2x milkingsystem, coupled with a similar calf mortalityand calving intervals in both systems, resultedin slightly higher indices, notwithstanding thesuperior calf growth in the 1x milking system.Parity of calving was not significant for any ofthe three indices, although the trend was towardreduced productivity for older cows.

The effect of year-season of calving wasimportant (P < .01), with highest indices beingachieved for parturitions occurring in the wetseason of 1986. Within a given year, indices forcows calving in the wet season were about 20%greater than for those calving in the dry season(Table 4). Effects of sex of suckling calf andtrypanosome infection status on productivityindices were not significant. Herd effects in 1xmilking system approached significance (P =.08) but not in the 2x system. When the pro­ductivity indices in this study were compared

Journal of Dairy Science VoL 74, No.5, 1991

MII...K PRODUcnON OF VILLAGE-RAISED N'DAMA CATILE

TABLE S. Comparison of productivity indices of N'Dama IIIId Zebu1 eattIe of various production systems.

Cow productivity indices

1607

Cattle breed System Location Source Index 1 1ndelt 2 Index 3

N'Dama

Zebu

Vtllage Gambia Cum:ot stndyStation Gambia (IS)Station Sc:ocgal (7)Station Sierra Leone (4)

Transbnman Mali (1.7)Agropastoral Mali (30)Settled Fulani,INigeria Cited in (1.7)TraditioDal Bot.swaM Otcd in (1.7)

73.582.670.135.537245.747.5612

32.6 140.630.5 138229.1 127.019.7 80.0

17.3 73.72

18.9 83.12

17.7 8022

18.8 89.82

1Figures for Zebu's adapted from Wagenaar et aI. (27).

2caIculated usinB figures for Index 1 IIIId adult cow weight.

with those achieved by the same breed kept atresearch stations (Table 5) at which milk wasnot extracted, the value achieved at the villagewas superior on indices 2 and 3. Stationanimals in most cases were supplement~fedandreceived better health care.

Thus, the higher production in the villagesystem indicates that a substantial pan of theproduction on station does not appear as har­vested output. The milk produced by cows ispresumably not utilized fully by the sucklingcalves. It would appear reasonable that at leastsome of the "swplus" milk be extracted forhuman use as long as the extraction does notjeopardize the welfare of the calf. The similarproductivity achieved in Ix and 2x milkingsystems (Table 4) supports this viewpoint.

A comparison of N'Dama and Zebu cattle(Table 5) managed under similar conditions andmilked for human consumption shows that theproductivity of the N'Dama was superior tothat of Zebu in all situations.

Repeatablllties

Repeatability estimates based on 198 recordsof 104 cows were .54 ± .01 for lactation milkofftake and .15 ± .01 lactation length. Thesevalues are within the ranges reported for othercattle breeds (21, 29), some of which aredescribed as possessing better "dairy" chara~

teristics than the N'Dama. The moderately highrepeatability estimate for milk offtake and thehigh persistency of milk yield during the first 6to 7 mo of lactation (3) suggest that it may bepossible to enhance the milking characteristicsof N'Dama cattle through genetic selection.

CONCLUSION

The results show that the N'Dama cattle,hitherto ignored as a provider of animal proteinfoe buman diets, presumably because of itssmall size, appears to have, on a metabolicweight basis, an overall performance superiorto the larger Zebu cattle. The better than ex­pected performance of the N'Dama in villagescompared with performance of N'Dama kept atresearch stations was due to milk offtake invillage herds. The major constraints to higherproductivity in the village systems appear to becalf mortality and nutrition of dams. Althoughthe major cause of calf mortality in the currentstudy was infectious diseases, the interactionbetween diseases and preweaning nutritionalstatus of the calf may be important and needs tothe studied.

Improvements in productivity through long­term genetic selection appears viable, but moreinformation on heritabilities and genetic co~lations among milk and other traits will beneeded in order to develop the most appropriateselection policy. Milking aspects of N'Damaare currently not a part of most research stationprograms. Because fanners with small holdingsconsider milk a priority output, it would appearreasonable to incoJpOrate the study of this traitamong the objectives in research aimed at ex­ploiting the productivity of the N'Dama breed.

ACKNOWlEDGMENTS

The authors wish to thank the director of theInternational Trypanotolerance Centre for sup­port and facilities. The inputs of M. Alberroand P. Jeannin during the early phase of the

Joarnal of Dairy Scicocc Vol. 74, No.5, 1991

1608 AGYEMANG ET AL.

project are kindly acknowledged. The usefulcomments on the manuscript by R. E. McDow­ell, North Carolina State University, L. D. VanVleck, University of Nebraska, and R. T. Wil­son and D. A. Little, the International Live­stock Centre for Africa are appreciated. Thesenior author is currently employed by Interna­tional Livestock Centre for Africa This studywas supported by funds from the EuropeanDevelopment Fund and executed jointly byILCA and the International Laboratory for Re­search on Animal Diseases.

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