Department of Animal Science, University o f Zimbabwe, PO Box MP 167, Mount Pleasant, Harare, Zimbabwe. SUMMARY. Six pairs of Mashona oxen ploughed ...
Trop. Anita. Hlth Prod. (1995)/7, 249-257
I M P R O V I N G F E E D I N G M A N A G E M E N T AND W O R K PERFORMANCE OF MASHONA OXEN THROUGH STRATEGIC SUPPLEMENTATION WITH COBSHEATH-GROUNDNUT STOVER J. FRANCtSand L. R. NvLovu Department of Animal Science, Universityof Zimbabwe, PO Box MP 167, Mount Pleasant, Harare, Zimbabwe SUMMARY
Six pairs of Mashona oxen ploughed dry, red clay soils in August (winter) and in mid-November (spring). Between September and November the oxen were randomly assigned to 3 feeding groups: no supplement (control), 400g/head per day of cobsheath-groundnut stover for 70 days and 800g/head per day of the same supplement for 35 days. Cobsheath-groundnut stover was fed in order to determine its potential as supplementary feed for draught oxen during the dry season. The liveweight (LW) lost by heavy tTxen during winter ploughing was lower (P < 0.001) than that of light oxen. During spring ploughing heavy oxen again lost less (P < 0"001) L W than light ones. In addition, non-supplemented oxen lost more L W than those supplemented. Therefore feeding strategies for Mashona draught oxen should aim at providing adequate nutrients to at least maintain L W during the dry season. Heavy oxen outperformed (P < 0.001) light ones during winter ploughing. Work output of supplemented oxen in spring was also significantly greater (P < 0.05) than that of non-supplemented ones. This result demonstrated the benefits of supplementary feed during the dry season. Concentrations of lactate and free fatty acids in plasma, heart rates and rectal temperatures increased (P < 0.05) markedly during work. The increases were higher (P < 0"05) for light oxen, particularly those not fed supplement. INTRODUCTION
Indigenous cattle (especially the Mashona breed) provide almost all the draught power for crop production in communal areas of Zimbabwe. The poor nutritional status of these cattle at the onset of the main cropping season limits timely ploughing and planting. This problem is linked closely to the questions of what, how much and for how long to feed in the preceding long dry season (May to November) to ensure that draught animals are in ideal body condition during the peak ploughing period (mid-Novemb~ to early January). Maize stover is the most abundant dry season feed resource for ruminant livestock in agroecological regions II and III of Zimbabwe (GFA, 1987). Extension workers usually advise farmers to harvest and feed it to milking cows and draught oxen in the dry season during which its availability to adult cattle is unlikely to exceed 2.5kg/head per day. Therefore judicious utiIisation of the stover is required if optimum benefits are to accrue to the farmer. Maize stover has a poor nitrogen content and low digestibility, implying that for it to be incorporated successfully into rations for productive animals its readily degradable fractions should be combined with sources of nitrogen. Conventional protein 249
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supplements can improve the utiIisation of maize stover by cattle and reduce considerably liveweight (LW) losses during the dry season. However, these supplements are too expensive to be afforded regularly by most communal area farmers. If possible, locally produced, affordable supplements should be identified. Cobsheath, despite its equally poor nitrogen content, has a better nutritive value than total maize stover (Goldschmidt, 1971) and could be a more valuable feed for draught cattle. Considerable amounts of groundnut stover are produced annually in communal areas of Zimbabwe. The stover is not utilised judiciously (Mombeshora et al., 1985), despite its high crude protein and mineral contents. The purpose of this study was to investigate the effects of feeding cobsheathgroundnut stover as a supplement for Mashona oxen prior to peak ploughing time in spring (October to November) on LW and work performance. It was also desirable to establish whether it would be better to feed small quantities of the supplement for a long period or larger amounts for a shorter duration prior to peak ploughing time. Biochemical and physiological parameters were monitored in order to provide comparative information on the magnitude of work stress between heavy and light Mashona Oxen, with or without supplement. MATERIALS AND METHODS
The study was conducted in Zimbabwe at Thornpark estates, from August to November. The estates lie about 17°55'S and 31°E at an altitude of 1,200m, and consist of moderately deep, well-drained red clay soils. The rainy reason extends from mid-November to April and annual rainfall normally averages 815ram. When ploughing was carried out in August mean daily ambient temperature was t8°C at the start of work, increasing to 24°C on completing work. In November the corresponding temperatures were 17°C and 30°C respectively. Twelve Mashona oxen with an average LW of 302 kg (range 240 to 375 kg) and aged 2 to 5 years were matched into working pairs according to weight and compatibility, and were dewormed with Ranide (Coopers Private Limited, Zimbabwe) at the beginning of the study. Maize stover and the natural pasture which the oxen grazed freely when they were not working or penned at night constituted the basal diet. Drinking water was provided ad libitum in water troughs located in the grazing areas but was not offered in night pens. Cobsbeath and groundnut stover were mixed in a 3 : 2 ratio to form the dry season supplement (70 g/kg DM crude protein (CP), 660 g/kg DM neutral detergent fibre (NDF)). Supplements were randomly assigned to 6 pairs (spans) of oxen such that there were equal numbers of heavy and light animals within each treatment (2 light and 2 heavy oxen). The supplement was fed to individual oxen at 07.30 h, immediately before they were released to graze. Treatment 1.--No supplement. Treatment 2.--400 g/head/day of cobsheath-groundnut stover fed for 70 days prior to ploughing in November, Treatment 3.--800 g/head/day of cobsheath-groundnut stover fed for 35 days prior to ploughing in November. All spans pulled right-hand mouldboard ploughs penetrating depths of 13 to 16cm on dry, red clay soils for 4 consecutive days in August (winter), working daily from 06.00 to 10.15h. They were rested for 15min, midway through each daily ploughing session. A ploughman controlled the same span throughout ploughing
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times, while a workmate led it. In early September supplementary feeding was started and continued up to late November. The oxen were then worked for a second 4-day period in November following the same regimen as that used in August. This second working phase represents the end of the dry season when cattle in communal areas would have lost body condition. During the feeding period, the oxen were weighed every 2 weeks shortly before being released to graze in the morning using a scale (Cattleway Marondera, Zimbabwe). The oxen were also weighed soon after work before they had access to feed and drinking water, on the first and fourth days of work. A hydraulic dynamometer was used to monitor draught forces (Newtons (N)) during work. Because of the jerky movements of walking oxen, mean dynamometer readings were taken at 5 rain intervals and averaged half-hourly in order to obtain a good estimate of the load. The distance covered (metres) and working time were measured using a tape measure and stopwatch respectively, and were used together with draught forces to calculate work in megajoules (M J) and power in watts (W). Area (m2) was obtained by multiplying the length of the ploughed strip of land by its width. Jugular vein blood samples were collected from all animals in ethylene diaminetetracetic acid (EDTA) anticoagulant on the fourth day of work 5 rain prior to work and 10, 30 and 70 min after completion of work. The blood samples were chilled in ice. Plasma was then collected after centrifuging at 3,000 rpm for 5 rain within 2 hours of bleeding, and stored at -20°C. Lactate, pyrnvate and FFA concentrations were then determined enzymaticaUy as outlined in the methods of Noll (I974), Czok and Lamprecht (1974) and Hron and Menahan (1981) respectively. A stethoscope was used to measure heart rates (HR) immediately before and after 2 hours of work, after 5 rain and 15 min rest, immediately after another 2 hours of work and 5rain and 15min after the second period of work. Rectal temperatures (RT) were measured at the same times as HR by inserting a clinical thermometer into the rectum of each ox. The measurements of HR and RT were made in the open field where the animals worked. Data were analysed using the General Linear Models (GLM) procedure of the Statistical Analysis Systems (SAS, 1985) software programme testing for effects of time of observation, weight class, treatment and weight class x treatment interaction. TABLE I
Effect on mean iiveweight (kg) of supplementing Mashona oxen with cobsheath-groundnut stover during the dry $eason
Treatment Days of supplement
TI
T2
T3
s.e.m.
0 14 28 42 56 70
295 293 289 285 280 276
300 302 304 304 302 301
315 312 309 310 311 312
12.8 12.4 11.4 10.6 10.0 9.7
Note: T1, T2 and T3 denote no supplement offered, receivingsupplement for 70 days prior to ploughing and receivingsupplement for 35 days before ploughing. s.e.m.mStandard error for comparing means.
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FRANCISAND NDLOVU T^eLe It Effect of liveweight of Mashona oxen on weight loss, work, power and area ploughed during winter ploughing Weight class Parameter
Heavy
Light
s.e.m.
Weight loss (%) Work (MJ/day) Power (kW) Area ploughed (m2/day)
2-7 8.4 591.8 2364-0
4-1 6-3 455-6 1513-3
0-04 0-09 6-82 28.28
Within subjects effects for liveweight changes observed during the non-working feeding trial, concentrations of plasma lactate and FFA, HR and RT were assessed by the repeated measures analysis of variance of GLM using time as the repeated level. Means were compared by the least squares procedure. RESULTS
There were no significant differences (P > 0.05) in LW among feeding groups up to day 56 of the trial. However, on day 70 mean LW of the control group was observed to be lower when compared with the 2 groups that were fed supplements ~ a b l e I). Non-supplemented oxen continuously lost weight from the first to the last day of the trial. On average, each ox lost 214 (s.e. 63.4) g/day, with heavy oxen losing more LW (6% of initial LW) than their lighter group mates (4% of initial LW). The oxen which were fed supplement for 70 days maintained LW. The remaining supplemented oxen lost weight continuously up to the time when supplementation with 800 g/head per day of cobsheath-groundnut stover was begun. Thereafter they regained LW, with light oxen tending to have better rates of gain (g/day) than heavy oxen. All oxen lost LW during the winter working period, with heavy oxen losing less (P < 0.001) than light ones (Table II). This trend was also observed during spring ploughing, particularly for non-supplemented oxen which lost significantly more (P < 0.001) LW than those supplemented. TABLeIII
Effect of liveweight and dry season supplementary feeding with cobsheath-groundnut stover on weight loss, work, area ploughed and power of Mashona oxen in spring Weight class Heavy Parameter
Weight loss (%) Work (MJ/day) Power (W) Area ploughed (m2/day)
TI
4.4 8"0 566.9 2157-0
T2 3' 1
7"8 544*0 2408-0
Light T3
2.4 8.5 607.4 2561-0
TI
6.4 5.4 395.9 13560
T2
4-0 7.1 491-7 1732.0
T3
4.5 6-1 443"6 1538-0
s.e.m.
0-08 0.25 17o47 62.57
Note: T1, T2 and 1"3 denote no supplement offered, receiving supplement for 70 days prior to ploughing and receiving supplement for 35 days before ploughing.
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PERFORMANCE OF MASHONA OXEN TABLEIV
Effect of liveweight of Mashona oxen on concentrations of lactate andfreefatty acids ( FFA ) in plasma during winter and spring ploughing
Observation time Winter 5 rain pre-work 5 rain post-work 30 rain post-work 70rain post-work Spring 5min pre-work 5 rain post-work 30 rain post-work 70rain post-work
Lactate (mg/lOOmi)
FFA (mmol~tre)
Weight class
Weight class
Heavy
Light
s.e.m.
Heavy
Light
s.e.m.
14.1 32.9 21-8 14-2
13.8 42.3 25.5 14"0
1.23 0.78 0-47 1-04
0.5 1"0 0-7 0"5
0.4 1'2 0.9 0-5
0.02 0.03 0.02 0.01
13.2 37.7 27-6 14-3
14-1 53.3 33-7 14.5
0.63 1.35 2.12 1.28
0.5 1.1 0.8 0"5
0.5 1"3 0.9 0"5
0"02 0.07 0-02 0.02
Daily work output, draught power and areas ploughed by heavy oxen in winter were significantly greater (P < 0.001) than those of light oxen (Table II). The same trend was also observed in spring but no significant difference (P > 0.05) in work performance was observed between the oxen fed supplement for 35 days and those fed for 70 days prior to ploughing (Table III). However, work, power and area ploughed by these supplemented oxen were significantly greater (P < 0.001) than for the nonsupplemented group (Table III). Plasma lactate and FFA concentrations increased significantly (P < 0-001) during T^aLE V
Effect of liveweightof Mashona oxen on heart rates and rectal temperaturesduring winter and springploughing Rectal temperatures (°C)
Heart rate (beats/minute) Observation time Winter 5 rain pre-work After 2h work 5 rain post-work 15 min post-work After 2 more h work 5 rain post*work 15 rain post-work Spring 5 rain pre-work After 2 h work 5 rain post-work 15 rain post:work After 2 more h work 5 win post-work 15min post-work
Heavy oxen
Light oxen
s.e.m,
Heavy oxen
Light oxen
s.e.m.
60 I 11 80 64 116 81 64
59 122 85 64 130 87 66
0-3 0"8 0"7 0.5 0"7 1"0 0-5
37,4 38"3 38"I 37"7 38"7 38"6 38'3
37"5 38"8 38"5 38"I 39-4 39"6 38-8
0-03 0-06 0"07 0.06 0-06 0.07 0"08
60 I 16 81 64 120 83 64
60 126 86 66 137 87 66
0"3 I-I 0"9 0-7 1'3 1.1 0"7
37.4 38-4 38"2 37"9 39"0 38"9 38-5
37"5 39" I 38"9 38"5 39-8 39-6 39-2
0"02 0-07 0.06 0-06 0-08 0.09 0-09
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FRANCIS AND NDLOVU
winter ploughing, but gradually decreased on cessation of work to reach pre-work concentrations within 70 minutes post-work (Table IV). The increases in lactate concentrations were more pronounced in tight oxen even though there were no significant differences (P > 0.05) in concentrations of FFA between heavy and light oxen. Highly significant increases (P < 0-001) in concentrations of plasma lactate and FFA were also observed during spring ploughing (Table IV). These increases were most striking for light, non-supplemented oxen but because of large variations between individuals these differences were not statistically significant (P > 0.05) across treatments and between weight classes. Resting concentrations were also realised within 70 min after completion of work. Heart rates and RT increased considerably (P < 0.001) during winter ploughing, especially for light oxen (Table V). A rapid decrease (P < 0.05) in HR was observed soon after completion of work, almost reaching pre-work states 15 rain post-work. In contrast, RT decreased slowly and failed to reach resting states 15 rain into the recovery period. Similar results were obtained during spring ploughing (Table V). Effect of supplementary feeding was also non-existent. DISCUSSION
Patterns of LW changes reported in this study suggested that cobsheath-groundnut stover enhanced the utilisation of natural pasture and maize stover by draught oxen resulting in either maintenance or slight overall LW gain. This effect was more dramatic in the group that was fed supplement for only 35 days, where supplementation reversed weight losses and resulted in LW gain. The LW losses observed during working periods indicated that the work regimen imposed was more severe for oxen weighing tess than 290 kg. It was also evident that animals under a poor feeding regimen were more stressed and suffered more rapid LW loss than those well-fed, which confirmed the findings of Bartholomew et al. (1993). The superior work performance of heavy oxen supported earlier reports (Howard, 1980; Francis and Ndlovu, 1993) which showed that heavy oxen always outperformed light ones. Studies conducted in Mati showed 2 that oxen fed supplements during the ploughing season could plough 1,737m/hour while those not supplemented ploughed 1,498 m2/hour (ILCA, 1986). These results showed a 14% increase in work output which could be attributed to provision of supplementary fe~d, in close agreement with results obtained in this study. Further studies at ILCA (Bartholomew, 1989) showed that increased body weight and condition, brought about by supplementary feeding, failed to improve work output of heavy oxen or to increase crop yields. It was concluded that there may be tittle benefit in providing supplementary feed to heavy oxen during the dry season. Bartholomew's results suggested the existence of a critical minimum LW and body condition, which if reached or exceeded would result in reduced work output even if supplement is offered. The relatively higher concentrations of lactate for light oxen implied that work stressed these animals more than heavy ones, resulting in increased anaerobic energy supply to working muscles. Accumulation of lactate in skeletal muscle inhibits the activity of phosphofructokinase and contractile property of muscle (Newsholme, 1981) thus leading to reduced working efficiency. In this study, smaller oxen started panting heavily after about one and a half hours during spring ploughing and became increasingly reluctant to work thereafter. Resting the animals for 15 min after 2 hours work did not appear to benefit the oxen inuch in the subsequent 2 hour working
PERFORMANCEOF MASHONAOXEN
255
session. These results supported the suggestion (Teleni and Hogan, 1989) that a resting period of more than 30 rain after working for 3 to 4 hours should be provided if work performance in the next working period is to be maintained or improved. The relatively higher concentrations of FFA in plasma of non-supplemented oxen implied that supplemented oxen obtained part of their energy requirements for work from cobsheath-groundnut stover and the rest from body fat depots. The contribution of FFA to energy expenditure increases from 40% in animals that are fed to almost 70% in fasted animals (Tdeni and Hogan, 1989). Working with Brahman x Friesian cattle that were walking for one hour daily on a treadmill and pulling 20 or 25kg weights suspended in a cage, Pearson and Archibald (1989) found that FFA concentrations decreased to resting states by 45 min after completing work. In our study, pre-work concentrations were achieved between 30 and 70 rain post-work. The increased HR observed during winter and spring ploughing reflected the increased cardiac output triggered in order to increase throughput of metabolic substrates to body tissues, particularly skeletal muscle. A strong positive correlation exists between HR and the rate of energy expenditure (Richards and Lawrence, 1984). Heart rates increased more for light oxen, which could mean that these oxen used up more energy than heavy ones. Bartholomew et al. (1993) reported that greater physiological stress manifests in maximum HR, reinforcing the assertion that the work regimen imposed in this study had more adverse effects on light oxen. Since the rate of decrease of HR to resting states may reflect the level of fatigue in draught animals (Lawrence and Pearson, 1993), light oxen and those not fed supplement were probably fatigued during work. This study has demonstrated that providing supplement for a short and long duration prior to peak ploughing time are equally beneficial feeding practices. Where resources permit, farmers should strive to at least maintain LW of their oxen during this period of nutritional deficiency. However, where labour bottlenecks exist, farmers would probably find it better to feed their animals much closer to the peak ploughing time. ACKNOWLEDGEMENTS
Financial support for this study was provided by the Rockefeller Foundation Southern Africa Agricultural Research Support Programme and the University of Zimbabwe Research Board. Accepted for publication November 1994 REFERENCES BARTHOLOMEW,P. (1989). Feeding strategies for draught animals: Feed supplementation and work output of oxen. International Livestock Centre for Africa (ILCA) Annual Report 1989, pp 69-70. BARTHOLOMEW,P. W., KBmE,T., LrrrL~ D. A. & BA, S. (1993). Effect of change in body weight and condition during the dry season on capacity for work of draft oxen. Tropical Animal Health and Production, 25, 50-58. CzoK, R. & LAMPREcerT,W. (1974). Pyruvate, phosphoenol pyrnvate and D-glycerate-2-phosphate. In: Methods of Enzymatic Analysis. (Ed. H. U. Bergrneyer). Second ed, Academic Press, London, UK, pp 1,446. F~Ncrs, J. & NDLOVU,L. R. 0993). Work capacity of Mashona oxen. Zimbabwe Journal of Agricultural Research, 31, 93-98. GFA (1987). Study on the economic and social determinants of livestockproduction in communal areas of Zimbabwe. Consultancy report prepared for the Ministry of Lands, Agriculture and Rural Resettlement, Harare, Zimbabwe.
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GOLDSCHMIIYt'~W. B. (I971). Crude protein content and digestibility of various parts of the maize plant. Rhodesia Agricultural Journal, 68, 70 (Abstract). HOWARD,C. R. (1980).The Draft Ox: Management and Uses. Zimbabwe Rhodesia Agricultural Journal, 77, 19-34. HltoN, W. T. & MmqAHAN,L. A. (1981). A sensitive method for determination of free fatty acids in plasma. Journal of Lipid Research, 22, 377-381. ILCA (1986). Serving AfricaxtAgriculture. ILCA Annual Report 1985/86. Addis Ababa, Ethiopia. L^wR~cE, P. R. & PeArSON,R. A. (1993). Experimental methods in draught animal science:the need for standardisation. In: Human and Draught Animal Power in Crop Production. (Eds D. H. O'Neill and G. Hendriksen). Proceedings of the Silso Research Institute--CEC/FAO workshop 18 to 22 Janua_ry 1993, Harare, Zimbabwe. FAO Rome, pp 36-39. MoMeeSxo~, B., AGYEMANG,K. & WILSON,R. T. (1985). Livestock ownership and management in the Chibi and Mangwende communal areas of Zimbabwe. Small Ruminant and Camel Group Document No. SRC2, ILCA, Addis Ababa. N~VSHOLMe,E. A. (1981). Control of carbohydrate utilisation in muscle in relation to energy demand and its involvementin fatigue. Medicine Sport, 13, 53-62. NOLL, F. (1974). Lactate:- Determination with LDH, GPT and NAD. In: Methods of Enzymatic Analysis (Ed. H. U. Bergmeyer), Second ed, Academic Press, London, UK, pp 1,475. PeAP.SON,R. A. & ARCHIBALD,R. F. (1989). Biochemicaland haematologicaichanges associated with short periods of work in draught oxen. Animal Production, 48, 375-384. RICHARD$,J. I. & LAWRENCE,P. R. (1984). The estimation of energy expenditure from heart rate measurements in working oxen and buffalo. Journal of Agricultural Science, Cambridge, 102, 711-717. SAS (1985). SAS User's Guide."Statistic. Version 5 ed. SAS Institute, Ind. Cary, N.C., USA. TI~LENI,E. & HOGAN,J. P. (1989). Nutrition of draught animals. In: Draught Animalsin Rural Development. (Eds D. Hoffmann, J. Nari and R. J. Petheram). ACIAR Proceedings Series, No. 27, ACIAR, Canberra, Australia, pp 118-133. AMELIORATION DE L'ALIMENTATIONET DES PERFORMANCE DE TRAVAIL DES BOEUFS MASHONA A L'AIDE D'UNE COMPLEMENTATION STRATEGIQUE D'ENVELOPPES DE MAIS-FANE D'ARACHIDE R~um~--Six paires de boeuf Mashona ont ~t~ utilis~spour labourer des sols d'argiles rouges secs en Aofit (hirer) et en mi-Novembre(printemps). Entre Septembre et Novembre, los boeufs ont ~t6 ~partis au hasard en 3 groupes de traitement alimentaire: pas de suppi~'mentation(contr61e), 400g par t~te et par jour de d'enveloppes de mais pendant 70 jours et 800 g/t~te et par jour du mime suppl~'mentpendant 35 jours. Enveloppes de mais-fanes d'arachide ont ~:t~utilis~s comme aliment pour d~terminer leur potentiel en qualit~ d'aliment de compl~nentation pour los boeufs de travail en saison s&:he. La porte de poids vif (PV) des boeufs lourds pendant les labourages d'hiver a ~t6 inf~rienre(P < 0,001) cello des boeufs plus l~gers, Durant los labourages de printemps, ies boeufs lourds ont ~galement perdu moins de poids vif (P < 0,001) que los l~gers. De plus, los boeufs non supplbnent~ ont perdu plus de PV que los suppl~ment6s.En consb]uence, les strategies d'aiimentation des boenfs de travail Mashona devraient tendre ~ apporter los nutriments adb]uats pour au moins maintenir le PV pendant la saison s~cbe. Los boeufs lourds ont de meilleures performances (P < 0,001) que los l~gers pendant los labourages d'hiver. Le rendement de travail au printemps des boenfs supplL,mentes est significativementplus grand (P < 0,05) que celtti des non-supplementk;. Ce r~sultat d&uontre le b~n~ficede la supplbrtentation alimentaire en saison s~che. Los concentrations plasmatiques en lactate et acides gras libres, los battements cardiaques et al t~rnp~rature rectale augmentent sensiblement (P < 0,05) lots du travail. L'augmentation est plus import&nte (P < 0,05) pour los boeufs l~gers, en particulier ceux n'ayant pas d'atimentation suppl~mentaire. MEJORA DE LA ALIMENTACION Y DEL RENDIMIENTO EN EL TRABAJO DE BUEYES DE RAZA MASHONA MEDIANTE LA SUPLEMENTACION ESTRATEGICA CON PERFOLLAS DE MAIZ Y TALLOS DE CACAHUETE R e s u m ~ S e i s pares de bueyes de raza Mashona se utifizaron para afar suelos secos de arcilla roja en agosto (invierno) y mediados de noviembre (primavera). Desde septiembre husta noviembre los animales fueron distribuidos al azar en 3 grupos: animales no suplementados (control), animaies suplementados durante 70 dias con 400g pot animal y dla de una mezcla formada pot tallos de cacachuete y perfollas de maiz, y animales suplementadosdurante 35 dias con 800 g por animal y dia de la misma media. Se utiliz6 la mezcla de peffollas de maiz y tailos de cacahuete para evaluar su potential como suplemento para bueyes de tiro durante la estacibn seca. Lns perfollas son las brficteas u hojns externas que protegen la mazorca de maiz.
PERFORMANCE OF MASHONA OXEN
257
Los bueyes m ~ pesados perdieron menos peso que los bueyes m~s ligeros tanto durante el periodo invernal de trabajo (P < 0-001) como durante el periodo primaveral (P < 0.001). Ademfis, los animales no suplementados perdieron m~s peso que los suplementados. En consecuencia, la alimentaci6n delos bueyes de tim de raza Mashona deberta proporcionales los nutrientes necesarios pant que al menos pudieran mantener su peso vivo durante la ~'poca seca. Los bueyes mils pesados rindieron nu~s que los bueyes mils ligeros (P < 0.001) durante el periodo inverhal de trabajo. Durante la primavera, el rendimiento en el trabajo de los animales supleraentados fue superior al de los animales no suplementados (P < 0.05). Esto demostr6 los efectos beneficiosos de la suplementacibn durante la 6poca seca. Tanto la concentracibn plasm~ttica de lactato y ~cidos grasos libres como la frecuencia cardiaca y la temperatura rectal aumentaron considerablemente durante el trabajo. El aumento fue superior (P < 0.05) en los animales ligeros, particularmente en aquellos que no recibieron suplemento.
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