1357-7298/98/6()()10595$20-00Animal Science 1998, 66: 595-605eJ 1998 British Society of Anima! Science

The effects of work and two planes of nutrition on trypanotolerantdraught cattle infected with Trypanosoma congolense

Bennisont, R. G. Clemencet, R. F. Archibald+, C. R. C. Hendyt and L. Dempfle

International Trypanotolerance Centre, PMB 14, Banjul, The Gambia

Abstract

Thirty-two N'Dama bulls aged 3 to 4 years were used to study the interactions between work, tl"ypanosomosis and

nutrition. The bulls were randomly allocated to two treatments, working (W) and non-working (N). Half in each

treatment were placed on an andropogon hay basal diet (B), the other half on a better quality groundnut hay diet

(H). Five days a week, four pairs ~f animals in the BW group and and four pairs in the HW group pulled weighted

sledges four times around a 2056-m track. Loads !L1ere set to ensure energy expenditure u'as equil'alent to 1.4 times

maintenance. After 4 weeks all 32 bulls were injected intradermally with 104 Trypanosoma congolense

organisms. The trial continued for a further 8 weeks.Trypanosome infection caused a significant (P < 0.001) decline in packed cell volume (PC V), and the anaemia was

more severe (P < 0.05) in working animals; three pairs in the HW group and two pairs in the BW group u'ere

withdrawn because PCV fell below 17%. Diet had no effect on PCV or parasitaemia. Infection caused a decline in

food intake (P < 0.001) but u1ith significant interactions between diet and work. Intake patterns were similar in the

BN and BW groups whilst the HW animals consumed significantly more groundnut hay compared with the HN

group (P < 0.01). However, nutrition had no significant effect on lap times or the team's ability to work under

trypanosomosis challenge. Post-infection, diet was the dominant factor determining weight change, HN and HW

animals weighed sign~ficantly more than BN and BW animals (P < 0.01) and the interaction between period, diet

and work demonstrated that BW had the lowest weights in the latter stages of the trial (P < 0.05).

The results suggest that supplementation with better quality forages confers no benefit to an animal infected with

trypanosomes. Nor can trypanotolerant cattle sustain long periods of work if subiected to a primary challenge of

trypanosomes.

Keywords: cattle, nutrition, trypanosomiasis, work.

an innate resistance to trypanosomosis (Roberts andGray, 1973; Murray et al., 1981) is an option for tsetseendemic areas.

Nutrition is a major problem for draught animals.While draught cattle have the advantage of beingable to utilize poor quality forages and crop residues,the peak periods of work are concentrated within thetime of greatest food scarcity i.e. at the end of the dryseason and beginning of the rains. Farmers in TheGambia respond to this constraint by storingcomparatively large quantities of groundnut hay(Arachis hypogaea). The hay is given as a supplementthroughout the dry season and early rains tomaintain body condition and weight in draughtcattle.

IntroductionIn sub-Saharan Africa expanding human populationshave resulted in increased pressure for croplandsand a concurrent requirement for an increase inlivestock and crop production. The promotion ofdraught animals within a mixed livestock croppingsystem is a means of increasing the area cultivatedand crop yields. However, a constraint to theexpansion of draught animals within the region isthe presence of tsetse transmitted trypanosomosis.The use of the N'Dama breed of cattle which exhibit

Present addresses: t NRI, Central Avenue, ChathamMaritime, Chatham, Kent ME4 4TB.i Centre for Tropical Veterinary Medicine, Universit}' ofEdinburgh, Easter Bush, Roslin, Midlothian EH25 9RG.

595

596 Bennison, Clemence, Archibald, Hendy and Dempfle

It has been suggested that work could increase thesusceptibility of draught animals to disease (Starkey,1981; Munzinger, 1982). Murray et ai. (1983) reportedthat the trypanotolerant mechanism can be reducedby stress factors such as work, pregnancy, lactation,inter-current disease and inadequate nutrition.Certainly there is now considerable evidence thatplane of nutrition and the degree of nutritional stressplaya significant role in the ability oftrypanotolerant animals to control anaemia duringthe course of a trypanosome infection (Agyemang etai., 1990; Romney et ai., 1997) However, detailedinformation on the effects of infection on work islimited. There is certainlv anecdotal evidence fromfarmers that draught cattle succumb to the diseaseduring periods of intense work. Similarly, in the1940s, the first attempts to demonstrate the value ofox drawn equipment to Gambian farmers failedbecause the animals were reported to suffer badlyfrom trypanosomosis (Sumberg and Gilbert, 1992).

Work treatments. The animals in groups HW, BWwere given a controlled amount of work toundertake. They worked in pairs pulling weightedmetal sledges round a 2056-m track, four circuits aday, 5 days/week (Monday to Friday), for the 12-week duration of the trial. Drivers were allocated toteams at random at the start of the experiment andremained with the same team for the duration of thetrial barring accident or illness. Work started atabout 09.00 h and continued until each team hadcompleted four circuits of the track. The teamsstarted at 2-rnin intervals and were encouraged towork at their own pace, overtaking as appropriate. Ifany team took more than 1 h to complete a single lapof the track, it was withdrawn from work for theremainder of that day.

The sledge loads were initially set at 17% of thecombined LW of each team based on the LW at thestart (week 1). This was reduced to 10% in weeks 2and 3 whilst the bulls became accustomed to work.The "'ork data from these three preliminary weekswere not used in subsequent analysis. From week 4,sledge weights were fixed at 12.5% of the team's LWin week 1 and remained at this level for the rest ofthe trial. The average draught force required by eachteam to pull its sledge was measured at the start ofweek 4 using an ergometer with a load cell(Novatech Ltd) and an odometer (Lawrence andPearson, 1985). The loads were set to ensureestimated energy expenditure during work wasequivalent to 1.4 X maintenance.

If guidelines for feeding draught cattle in tsetseendemic areas are to be developed, a betterunderstanding of the interaction between work,trypanosomosis and nutrition is needed. Thus theobjective of this trial was to investigate the effect ofnutrition and work on cattle artificiallv infected withTrypanosoma congolense using diets 0 that reflected

existing feeding strategies in The Gambia, wheredraught bulls are given diets dominated bygroundnut hay and poor quality native pasture.

Dietary treatments. The quantity of food offered toindividual animals was calculated on the basis of themean LW of the initial sub-groups i.e. 180 and200 kg. The animals on the basal diets (BN and BW)received the equivalent of 1.2 g dry matter (DM) perkg LW of rice bran (Oryza sativa) and 9.6 g DM perkg LW of groundnut hay. Animals on the 'high' diet(HN and HW) received the equivalent of 1.2 g DMper kg LW of rice bran and 17.7 g DM per kg LW ofgroundnut hay, a level set close to maximumvoluntary intake while ensuring there were nogroundnut hay refusals in the pre-infection period.All animals were offered chopped andropogon hayad libitum at 1-4 times the previous day's intake.Sesame cake (Sesamum indicum) was introduced at aconstant 1.9 g DM per kg LW for all treatments fromweek 8 based on the mean weights of the subgroupsat the start of the trial. This was in response to LWlosses during infection being greater than expectedfrom the intake data collected, raising the possibilitythat the lack of protein in the diet was inhibitingrumen function.

Material and methodsExperimental designTreatments and animals. Thirtv-two N'Dama bulls,aged 3 to 4 years, were selected for the study from anoriginal group of 41, on the basis of their live weight(L W) and willingness to work. Because L W at thestart of the trial ranged from 174 to 214 kg, animalswere allocated to two subgroups consisting of the 16lightest and the 16 heaviest with mean live weightsof 181 (s.e. 1.68) and 203 (s.e. 1.48) kg respectively.The animals from the two subgroups were thenrandomly allocated to two treatments, working (W)and non-working (N). Half the animals in each of thetwo treatments were placed on a basal diet (B), ofpredominantly andropogon (Andropogon gayanus)hay and the other half, on a better quality diet (H)dominated by groundnut hay. This ensured thatthere was an equal distribution of heavy and lightanimals in the four treatments, basal non-working(BN), basal working (BW), high non-working (HN)and high working (HW). There was also anadditional pair of animals on the HW diet that wasused to pull an ergometer to measure work loads(team 9).

The animals were given food and wateredindividually once all animals had completed their

1~

I

T rypanosomosis, work and nutrition in cattle 597work, the non-working groups were given food atthe same time. The bran (and sesame) was offeredfirst, followed by groundnut hay and finallyandropogon. The groundnut hay refusals werecollected by 15.00 h, the andropogon refusals werecollected the following morning. Table 1 summarizesthe diets.

constant throughout the experiment. NE expenditurefor each bull was calculated using the factorialequation (Lawrence, 1985). The metabolizable energy(ME) requirements of the bulls were estimated byassuming that the efficiency of utilization of ME forwork was the same as for maintenance (km)(Matthewman and Dijkman, 1993). ME requirementsfor work were calculated by dividing NEexpenditures by km where km = 0.35qm + 0.503 and qm= metabolizability of the diet given (ME/GE)

(Agricultural ~esearch Council, 1980). The MErequirement for maintenance (MEm) of the N'Damabulls was assumed to be 132.5 kJ Ikg LW.

Table 1 Composition of the diets offered

Foods offered g dry matter per kg live weight

Groundnut Andropogon Ricehay hay bran Sesamet

BasalHigh

9.417.7

ad libitumad libitum

1.21.2

1.91.9

t Introduced from week 8.

Live weight. Live weights were recorded twiceweekly, in the morning before feeding and work.

Food intake r~fusals and analysis. Voluntary OM intakewas recorded daily throughout the trial by weighingfood offered and total food refusals. Separate dailysubsamples from the food offered and refused werepooled over a 7-day period, dried in an oven at 60°Cto constant weight, ground through a I-mm screenand stored for analysis. The followingdeterminations were made on the weekly pooledsamples: OM, organic matter (OM), nitrogen (N),neutral-detergent fibre (NDF) and add-detergentfibre (ADF). The ME values were taken from theliterature.

Trypanosome infection. At the beginning of \,'eek 4 allanimals, except team 9, were intradermally injectedwith 1 ml mice blood containing 104 T. congolenseorganisms prepared from a clone derivative ofT. congolense known as ITC 84 (Dwinger et al., 1992).

Management and health. At the start of the trial all 34bulls were injected with 1'0% w I v ivennectin(Ivomec: Merck Sharp and Dohme) to eliminateinternal and external parasites. All animals weretreated with 7.0 mg/kg LW diminazene aceturate(Berenil; Hoechst) 8 weeks post infection. Bulls wereretired from work for the remainder of the trial iftheir blood packed cell volumes (PCV) fell below1~/o, a threshold that ensured all animals survivedthe trial (an animal would also have been withdrawnand treated with Berenil if the PCV had fallen below15%, although this did not occur).

Haematoiogicai measurements. Blood samples werecollected thrice weekly from the jugular vein withethylene diamine tetra-acetic acid coated vacutainers.The samples were examined by the buffy coat darkground / phase parasitological technique to detectpresence of trypanosomes and to quantify theintensity of infection as a parasitaemia score (Murrayet ai., 1977). The PCVs were determined using thestandard microhaematocrit technique.Measurements and observations

Work. The lap times and number of laps completedwere recorded daily for each team, throughout thetrial. The distance travelled and work done by team 9were measured weekly throughout the trial using theergometer and odometer. The average draught forcerequired by the team to pull the sledge wascalculated by dividing the work done by distancetravelled. The net energy (NE) expenditure for workof each bull in team 9 was estimated from work doneand the distance travelled using the factorialequation developed by Lawrence (1985).

Statistical analysisLive weight, food intake and haematological data. The L Wand food intake data were divided into three distinctperiods, period 1 (pre-infection weeks 1 to 4), period2 (post-infection weeks 5 to 7) and period 3 (post-infection weeks 8 to 12). The data were analysedusing the general linear models (GLM) procedure ofthe Statistical Analysis Systems Institute (1994). Themodel included the individual effects of age, weightat the start, period, week (nested within period), diet,work, animal (nested within age, weight at start, dietand work) and period X animal (nested within age,weight at start, diet and work). The interactionsbetween diet, work and period were tested. Acontrast analysis, comparing periods 2 and 3 withperiod 1, was used to identify the period in whichthe interaction occurred. Statistical significance wastested using the F test.

The work done by the other eight teams in the BWand HW treatments was estimated from the distancetravelled by the team each day multiplied by theteams' average draught force measured in week 4.Weekly average draught force values were comparedwith that of team 9 at the start of week 4, when thesledge weights were fixed to ensure they remained

598 Bennison, Clemence, Archibald, Hendy and Dempfle

Table 2 Effects of diet and work before infection (period 1) and after infection (periods 2 and 3) with T. congolense on mean packed cellVolullle (PCV) (':i,)

Diet Work Nc 2 3 Significance of effects

21.218.720.819.2

...BBHH

NWNW

8888

3().028.930.529.9

26.625.427.426.4

Subclass meansBH

Diet 29.530.2

26.026.9

19.920.0

1616

PeriodWeek (period)DietWorkDiet X workPeriod X dietPeriod X workPeriod X diet X workAnimal

NW

30.229.40.56

27.025.90.6()

21.018.90.5()

Work 1616

s.e.-t Codes are: B = basal; H = supplemented with groundnut hay; W = working; N = non-working.

Using the GLM model described, the least-squaremeans could not be estimated because animals werewithdrawn from the trial in periods 2 and 3 resultingin empty cells. The results presented in Tables 2 and3 are unadjusted means for each treatment with anaccompanying standard error of the mean. The dataof animals withdrawn from work in period 3 werealso included because, with the exception of L W andPCV, there was no significant difference between themeans of the 'survivors' and those that were too sickto complete the work programme.

Work output data. Lap times for weeks 4, 5 and 6 to 7were analysed separately using a balanced multi-way ANDV A to examine the effects of diet, day of the

week, lap and team and their possible interactions.Team mean lap times were further analysed using atwo-way ANOYA to look for significant differencesbetween weeks. The post-infection analysis wasrestricted to weeks 6 and 7 when all teams werebeing worked; once teams were withdrawn fromwork there were insufficient replicates in eachtreatment group for reliable analysis. Week 5 wasconsidered a pre-patent period before the acutephase of infection.

ResultsPCV and dark ground scoresAll animals became infected with trypanosomes andremained so until treatment with Berenil. Infection

Table 3 Effrcts of diet and work before infection (period 1) and after infection (periods 2 and 3) with T. congolense on mean live

u!eights

Treatmentt

2 3 Significance of main effectsDiet Work No.

182175188184

.........

NWNW

188188192188

187184193190

BBHH

8888

0.056Subclass means

BH

178185

...0-056...

185192

Diet 1616

188190

Weight at startPeriodWeek (period)DietWorkDiet X workPeriod X dietPeriod X workPeriod X diet X workAnimal185

1792.5

190188

2.3

190187

2-4

Work NW

1616

s.e.

t For treatment codes see Table 2.

Trypanosomosis, work and nutrition in cattle 599220

210 ~-_oC"-

~

-*---:6.--'"bOC

.:fo

.~OJ;>;:j

.,.&- -~- -c--~-

~~

Infection170

1602 3 4 8 9 10

Period 3

11 124 Period 1 ~ Period 2 --+

Weeks

Figure 1 Effects of infection with T. congolense and diet on the mean live weights of working (BW (~) and HW (0)) and non-working (BN (.A.) and HN(8») bulls (including team 9 (~), uninfected).

caused a significant decline in PCV in periods 2 and3 (P < 0.001; Table 2). Diet had no significant effect,whilst in period 3, working animals had significantlylower PCVs (P < 0.05). Working animals were lessable to control anaemia, five of the eight teams werewithdrawn from work because the PCV of one orother of the bulls dropped below 17%; three in theHW group and two in the BW group. No animal waswithdrawn from the non-working groups (BN andHN). As expected when the PCV is used as thecriterion for withdrawal from work, the mean of thesurvivors in period 3 was higher than that of thosewithdrawn, 20.4 (s.e. 0.48) compared with 18.0 (s.e.0.85), respectively (P < 0.001).

(periods 2 and 3), all animals lost weight and therewere significant interactions between period, dietand work on LW. Animals on the diet dominatedby groundnut hay (HN and HW) weighed onaverage 4.18 (s.e. 1.50) kg more in period 2 and 4.53(s.e. 1-47) kg more in period 3 (P < 0.01) than those onthe diet dominated by andropogon hay (BN and BW).Work had no significant effect on L W in the initialstages of infection (period 2) but by period 3 workinganimals (BW and HW) weighed on average 3.93 (s.e.147) kg less (P < 0.01) than their non-workingcounterparts. By period 3, the interaction of period,diet and work suggested that working animals on thebasal diet had significantly the lowest LW at 6.9 (s.e.2.95) kg less than other groups (P < 0.05).Comparison of the LW of the working bulls (BW andHW) indicated that those animals that werewithdrawn from the work programme weighedsignificantly (P < 0.001) less in period 1 than thosethat survived and worked until the end of the trial(182 (s.e. 3.8) kg v. 197 (s.e. 3.0) kg).

The overall mean dark ground (DC) scores inperiods 2 and 3 were 3.12 (s.e. 0.08) and 3.46 (s.e.0.14) and the parasitaemias in period 3 weresignificantly higher (P < 0.05). The lower PCVs in theworking animals (BW and HW) were accompaniedby significantly (P < 0.01) higher DG scores in bothperiods: 3.37 (s.e. 0.1) compared with 2.88 (s.e. 0.1) inperiod 2 and 3.86 (s.e. 0.17) compared with 3.05 (s.e.0.17) in period 3. Diet had no significant effectneither was there anv interaction between diet andwork on parasitaernia.

Figure 1 illustrates the change in mean LW of thefour treatment groups and team 9 (uninfected) as thetrial progressed. Once sesame had been introducedin week 8, the two bulls in team 9 gained 0.339 (s.e.0.054) kg/ day compared with the infected bulls onsimilar diets, the HN and HW groups, which lost onaverage -{}.060 (s.e. 0.048) kg/ day and -{}.165 (s.e.0.054) kg/ day respectively.

Live weightPre-infection (period 1), diet and work had nosignificant effect on L W (Table 3). Post-infection

200

190

180

Food composition (g/kg dry matter)

9.6 ~ OM per kg LW and the animals ate all that wasotiered throughout the 12-week period irrespectiveof work or infection (see Figure 2a). However, adifferent pattern of intake emerged with the HN andHW groups offered 17.7 g OM per kg LW ofground nut hay. In the pre-infection period allgroundnut hay was consumed. Infection in period 2resulted in a significant decline in groundnut hayintake equivalent to -1.23 (s.e. 0.27) g OM per kg LWper day (P < 0.05). This decline predominantlyoccurred within the HN group and persisted intoperiod 3. By period 3 there was also a significant

Food intakeTable 4 summarizes the nutrient composition of thefoods offered and refused. The results indicate thatthe bulls rejected components of the diet thatcontained higher levels of fibre, particularly AOF.Table 5 summarizes the mean food intakes for thethree periods and the significance of infection, work,and diet on the different components of the diet.Figure 2 illustrates the pattern of groundnut hay andandropogon intakes in g OM per kg L W.Groundnut hay. Within the basal groups (BN andBW), daily ground nut hay intake was constrained to

>r treatment codes see Table 2

Bennison, Clemence, Archibald, Hendy and Dempfle602

Table 7 Mean lap times for all u'Orking teams (BWand HW)before and after infection with T. congolense

Work output and energy expenditureThe mean work output of team 9 measured with theergometer was 2-13 (s.e. 0.030) MJ / day within arange of 2.02 to 2.27 MJ / day. The average draughtforce required to pull the sledge varied from 244 to276 N (mean of 258 (s.e. 1.8) N). The mean MEexpenditure for work (MEwork) of the bulls in team 9was 10.08 (s.e. 0.946) MJ per head per day or 50 (s.e.0.4) kJ / kg per day, proportionately 0.38 of theenergy requirements of an animal for maintenance.The estimated MEwork of the bulls in the other eightteams were very similar ranging from 48 to 58 kJ / kgper day with an overall mean of 53 (s.e. 0.2) kJ /kgper day.

Lap

1 26:00 00:18 25:34 00:23 31:28 00:472 27:13 00:36 26:18 00:40 33:05 00:593 27:56 01:02 26:08 00:26 34:36 01:134 28:08 00:21 27:21 00:38 34:07 01:05

Significance' s.e.d. 00 : 47 00 : 27 00 : 57

No. 40 40 80 Until the end of week 4 when the bulls were infected,all teams worked well, easily completing their fourlaps of the track each day. The uninfected pair ofbulls (team 9) continued to work well thereafter,completing the 12 weeks of work, and indeed gettingfitter as the trial progressed, as indicated bydecreasing lap times. In contrast only three of theeight infected teams were able to work for the full 12weeks of the experiment, because the PCV of one orother of the bulls in the team had dropped to 17%.Three teams on the HW were retired in weeks 9, 8and 11 respectively, and two teams on the BWtreatment in weeks 8 and 7. Table 6 illustrates laptimes expressed as a proportion of the lap timeimmediately prior to infection (week 4).

t Lap times of weeks 6 and 7 combined

Total food intake. Post-infection, work had asignifi~ant effect on daily total DM intake (P < 0.05)whilst diet had a significant effect on total OM intakethroughout the trial (P < 0.01; Table 5). Animalsgiven the higher levels of groundnut hay (HN andHW) had higher mean daily intakes than those onthe andropogon hay basal diet (BN and BW).Infection significantly (P < 0.001) reduced total foodintake in period 2; the apparent recovery of totalintake in period 3 was partly a consequence of theintroduction of sesame cake in period 3. In period 3,there was also a significant interaction (P < 0.01)between work and period with the working groups(BW and HW) eating 1.15 (s.e. 0.4) g/kg LW of OMmore than the non-working groups (BN and HN).

Comparison of lap times (Table 7) showed that theteams slowed down significantly once the infectionwas established (P < 0-001). The mean lap timesduring weeks 4 and 5 of 27 min 19 s and 26 min 20 srespectively were not significantly different.However, both were significantly lower than the lapmean during the infected period, 36 min 46 s.Nutrition had no significant effect on lap times or onthe ability of a team to work throughout the

experimental period.

Estimated metabolizable energy and crude protein intakes.Based on the food intake data, the estimated. dailyME intake of the BW and HW groups during period1 was 170 kJ Ikg LW and 200 kJ Ikg LW respectively.This was equivalent to 1.3 X maintenance for the BWgroup and 1.5 X maintenance for the HW group.During period 3, the estimated daily ME intake of theBW and HW groups was 173 kJ/kg LW and 207 kJIkg LW due to the introduction of sesame whichallowed the animals to maintain ME intake throughan increase in the energy concentration of the dietdespite changes in forage intake. The MEconcentration (MID) of the BW diet increased from8.8 to 9.6 MJ/kg DM, the HW diet correspondinglyincreased from 9.8 to 10.2 MJ Ikg DM.

During the course of a working day there was asignificant decline in speed with each successive lap,irrespective of the diet or day of the week (see Table7). Similarly, once the animals were infected theyslowed down over the course of each week from amean of 29 min 10 s per lap on a Monday to 38 min2 s by Friday (s.e.d. :t 1 min 30 s) (P < 0.001).

DiscussionGambian farmers start working N'Dama bulls whenthey weigh between 170 and 200 kg. It can beassumed that the bulls used in this trial arerepresentative of animals in their first workingseason. The draught force imposed in this trial, anaverage of 6.5% of LW, was generally less than that

In period 1, the estimated crude protein (CP) contentof the BW and HW diets was 51 g/kg OM and 72 g/kg OM, both marginal to the animals requirements.The introduction of sesame increased the CP contentof the BW diet to 96 g/kg OM and in the HW groupto 102 g/kg OM.

Trypanosomosis, work and nutrition in cattle 603observed on-farm, which ranged from 6.8 to 19.3% ofLW (Afford, 1994). The diet initially offered wassimilar to that used by farmers at the end of the dryseason, groundnut hay in varying proportions, poorquality native pasture and limited amounts of bran.Oilseed cakes are generally not available to farmersalthough the response of team 9 to sesame cake inperiod 3 illustrates their desirability (Figure I).

depending on the nutrient composition of the dietand the energetic demands of the animal. Thissuggests that anorexia during trypanosomosis is alsoaffected by physiological and physical intakemechanisms, even if it is induced by cytokines.

The ability of the HW animals to maintaingroundnut hay intake at proportionately 0.94 of pre-infection levels would imply that the effects oftrypanosomosis on work would be limited comparedwith the BW animals. Certainly, the levels of intakein the HW group were sufficient for maintenanceand work. However, nutrition had no significanteffect on lap times or on the team's ability to workthroughout the experimental period. Only three ofthe eight teams infected with trypanosomosis wereable to work for the full 12 weeks, two in the BWgroup and one in the HW group. The teams wereretired from work because one or other of the bullswere severely anaemic (PCV < 17%). By period 3 thePCVs of working animals were significantly lower(P < 0.001) which was accompanied by higher DGscores.

The diet offered to the HN and HW groups wassufficient to satisfy their ME requirements formaintenance and work irrespective of theirandropogon hay intake. The BN and BW groupswere only able to satisfy their requirements byconsuming substantial amounts of andropogon hay.To achieve an ME intake of 1.4 X maintenance, theBW animals would have had to consume about 10 gOM per kg L W of andropogon hay each day, a levelof intake approached only in the pre-infectionperiod. The food intake results (Table 5) suggest thatprior to infection the BW group had only a slightenergy deficit, whilst the HW group had easilysufficient energy for maintenance and the workimposed. The mean CP contents of the diets inperiods 1 and 2 were 50 to 70 g/kg OM, marginal torequirements. However, it should be rememberedthat the diets were initiallv based on foods availableto local farmers. A protei~ deficit would explain thelimited L W gain in the non-working groups (BN andHN) in period 1 and their greater than expectedweight loss during infection. Ultimately, sesame cakewas introduced into the diet in period 3 in anattempt to stabilize the weight loss, as there wasconcern that rumen function was impaired.

The lack of a difference in lap times between theworking groups suggests anaemia duringtrypanosomosis infection is possibly the major factorgoverning work output due to a decline in theoxygen carrying capacity of the blood. Payne et al.(1991) questioned whether the maintenance of anelevated body temperature in T. evansi infectedbuffaloes resulted in a reduction in energy availablefor metabolic activity and work as the metabolic rateof the animal has to be increased. The lack of anydifference between the HW and BW groups wouldimply that this was not a primary factor causing thereduction in work rates in N'Dama bulls.

This trial d~monstrated significant changes in foodintake in response to infection and the diet offered.Diet quality influenced total food intake; animals inthe groups (HN and HW) receiving the higher levelsof groundnut hay had significantly (P < 0'01) higherfood intakes. Infection resulted in a decline in foodintakes but there were also significant (P < 0'01)interactions between period, diet and work. Bothbasal groups (BN and BW) had simjlar patterns offood intake, showing a decline in response toinfection, which is consistent with literature reports(Verstegen et al., 1991; Zwart et al., 1991; Romney etal., 1997). A different pattern emerged with the dietscontaining higher levels of groundnut hay (groupsHN and HW). Essentially, animals responding to thedemands of work, appeared to be able to maintainfood intake during infection if the diet included ahigher quality component equivalent to groundnuthay (a legume). While the control mechanismgoverning food intake during the course of infectionsis thought to be cytokine mediated (McCarthy et aI.,1985; and van Miert et al., 1986), this studydemonstrated that the severity of anorexia will vary

Pre-infection, diet and work had no significant effecton LW. Post-infection (periods 2 and 3) diet qualitywas the dominant factor in determining weightchange, the animals on the basal diet weighingsignificantly less by period 2. Work had nosignificant effect on L W until period 3 when workinganimals lost significantly more (P < 0.01). Thesignificant interaction between diet, work and period(due to the low LW of BW animals in period 3(P < 0.05») indicates a cumulative effect on LW as thetrypanosomosis infection progressed. Previousstudies of the interaction between nutrition andtrypanosomosis (using the IL1180 strain of T.congoiense) in N'Dama cattle suggested that weightchange was primarily a function of a change in foodintake as a consequence of infection and not a changein metabolism (Romney et ai., 1997; Akinbamijo et aI.,1997). However, there is some indication from thistrial that a change in metabolism in response toinfection was also responsible for the weight loss.

604 Bennison, Clemence, Archibald, Hendy and Oempfle

The mean daily weight loss of -0.060 (s.e. 0.048) g/day exhibited by the HN group in period 3 wasevidence of a metabolic cost of infection, consideringthe estimated ME intake was 36.3 MJ (equivalent to1-4 X MEm) and the crude protein content of the dietwas 98 g/kg OM. Dwinger et al. (1992) and Osaer etal. (1994) concluded that ITC 84 is a more virulentstrain of T. congolense than the IL1180 strain andthese results indicate that there is a substantialmetabolic cost associated with ITC 84. Authie (1994)reasoned that the virulence of a trypanosomeinfection could be related to the excessive productionof cytokines and the release of secondary compoundsinto the host's blood stream when successivepopulations of trypanosomes are lysed byantibodies. If so, virulence is a factor that requiresfurther consideration as it appears to influence theseverity of the disease and the host response.

This study has a number ot practical implications forfarmers and organizations wishing to promotedraught N'Dama oxen in areas of hightrypanosomosis challenge. The results suggest thatsupplementation with better quality forages, such asgroundnut hay, confers no benefit on the workingability of the animal if infected with trypanosomes.Nor is it likely that trypanotolerant cattle would beable to sustain long periods of work if subjected to anew serodeme of trypanosomes, which agrees withthe report by Ravindran et ai. (1990) in Liberia. Giventhe importance of draught cattle to the income andfood security of smallholder farmers, chemotherapyis necessary for N'Dama cattle if thev becomeinfected dilring the stressful working period.However, further study is required to assess whetherthe control of trypanosomosis is improved iftrypanotolerant draught animals first develop anacquired immunity through the repeated exposure tolocal strains of the disease. By artificially challengingthe bulls with a new strain of trypanosomosis, thistrial only tested the innate resistance of the N'Dama,but the trial illustrates the importance ofchemotherapy if draught N'Dama cattle are to bepromoted in new tsetse endemic areas.

AcknowledgementsThis research was funded by the Overseas DevelopmentAdministration (ODA), London. The authors would like toexpress their thanks to the livestock assistants and fieldstaff at ITC for their hard work and commitment to the trial.

Agyemang, K., Dwinger, R. M., Touray, B. N., Jeannin, P.,Fofana, D. and Grieve, A. S. 1990. Effects of nutrition onthe degree of anaemia and liveweight changes in N'Damacattle infected \\'ith trypanosomes. Liroestock ProductionScience 26: 39-51.

Akinbamijo, O. 0., Bennison, J. J., Romney, D. L.,Wassink, G. J., Jaitner, J., Clifford, D. J. and Dempfle, L.1997. An evaluation of food intake, digestive physiologyand live-weight changes of N'dama and Gobra zebu bullsfollowing experimental Trypanosoma congolense infection.Animal Science 65: 151-158.

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(Received 4 October 1997-Accepted 12 ./lJovember 1997)