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Preweaning performance of Yankasa sheep under semi-intensive management

O.A. Osinowo, B.Y. Abubakar, M.E. Olayemi, R.O. Balogun, O.S. Onifade, A.A. Adewuyi, A.R. Trimnell and F.O. Dennar

National Animal Production Research institute (NAPRI)
Ahmadu Bello University, Zaria, Nigeria


Summary
Introduction
Materials and methods
Results and discussion
Conclusion
Acknowledgements
References


Summary

Preweaning growth traits and weaning rate of Yankasa sheep under a semi-intensive management system with twice-yearly lambings were studied for nine years at Shika, in the subhumid zone of Nigeria.

Least squares means ( ± SE) for birth weight (BW), 90-day weaning weight (WW), average daily gain to weaning (ADO) and weaning rate (WR) were 2.51 ± 0.01 kg, 10.87 ± 0.08 kg, 91.86 ± 0.91 g/day and 77.8 ± 1.0%, respectively. BW, WW and ADG were significantly (P<0.001) affected by dam parity and the lamb's litter size, sex, month and year of birth. WR was significantly (P<0.01) affected by parity, litter size, month and year of birth but not by sex of lamb (P>0.05). Preweaning growth performance was generally better in the wet seasons than in the dry seasons while the reverse was true for weaning rate.

Performances présevrage du mouton Yankasa élevé en système semi-intensif

Résumé

Les paramètres de croissance présevrage et les taux de sevrage du mouton Yankasa élevé selon un mode semi-intensif, avec deux agnelages par an, ont été étudiés sur une période de neuf ans à Shika, dans la zone subhumide du Nigéria.

Les moyennes des moindres carrés ( ± erreur type) du poids à la naissance, du poids au sevrage à 90 jours, du gain moyen quotidien (GMQ) jusqu'au sevrage et du taux de sevrage étaient respectivement de 2,51 ± 0,01 kg, 10,87 ± 0,08 kg, 91,86 ± 0,91 g/jour et 77,8 ± 1,0%. La parité de la mère, la taille de la portée, le sexe des jeunes, et le mois et l'année de naissance avaient un effet significatif (P<0,001) sur les poids à la naissance et au sevrage et sur le GMQ. A l'exception du sexe des agneaux (P> 0,05), ces mêmes paramètres avaient aussi un effet significatif (P<0,01) sur le taux de sevrage. Les performances de croissance avant le sevrage étaient généralement meilleures en saison des pluies alors que l'inverse était vrai pour le taux de sevrage.

Introduction

The preweaning traits of sheep which influence flock productivity include birth weight, weaning weight, average daily gain to weaning and weaning rate. These traits are in turn influenced by genetic and environmental factors. For a given breed, influencing environmental factors may include dam parity and type of birth and sex, month and year of birth of young (Terrill, 1966).

The Yankasa sheep is the most numerous breed of sheep in Nigeria and also has the widest distribution, being found throughout the subhumid and semi-arid zones (FDLPCS, 1991). It is estimated to constitute about 60% of the national sheep population of 22.1 million (Osinowo, 1992). Preweaning traits have been studied in Yankasa sheep (Adu et al, 1979; Adu and Buvanendran, 1982; Taiwo and Buvanendran, 1985; Hassan, 1987). However, these earlier studies were carried out with smaller data sets of less than four hundred records.

This study re-examined preweaning traits of Yankasa sheep under semi-intensive management at Shika in the subhumid zone of Nigeria, using a much larger data set collected over a nine-year period.

Materials and methods

The Yankasa sheep flock from which the data were obtained was located at the National Animal Production Research Institute (NAPRI), Ahmadu Bello University, Shika, Nigeria, latitude 11°12'N, longitude 7°33'E and 610 metres above sea level (masl). The climate is subhumid and the vegetation zone is Northern Guinea Savanna. Mean annual rainfall and temperature recorded at Samaru, 10 km from Shika, were 1107 mm and 24.4°C, respectively. The seasonal distribution of rainfall is approximately 0.1% in the late dry season (January-March),25.8% in the early wet season (April-June), 69.6% in the late wet season (July-September) and 4.5% in the early dry season (October-December). Fodder is generally scarce and of low quality in the late dry and early wet seasons. It is in abundant supply and of relatively good quality in the late wet and early dry seasons.

The origin and management of the Yankasa sheep flock studied have been previously described (Osinowo, 1982; Osinowo and Ekpe, 1985). In 1987, the flock was enlarged from 100 to 300 ewes by additional purchases from livestock markets in the same North Western region of Nigeria. The sheep were managed under a semi-intensive system. This involved grazing on improved and sown pastures for 6-8 hours daily, with 0.3-0.5 kg/day of a 15-20% crude protein concentrate supplement throughout the year, depending on the animal's physiological status (pregnant, nursing or dry). The animals were housed in well ventilated pens overnight. The ewes were routinely bred to lamb twice a year under an accelerated lambing programme. The lambs were weaned at about 90 days of age.

Data on birth weight (BW), weaning weight (WOO) and weaning rate (WR) were collected over nine years, from 1983 to 1991. Preweaning average daily gain (ADO) was calculated for each lamb after age-correction of WW to 90-day weight. Factors included in the study were parity of dam (1-6) and lamb litter size (single vs twin), sex (male vs female), month of birth (January-December) and year of birth (1983-1991) of the lambs. After editing, 2020 BW, 1203 WW, 1203 ADG and 1576 WR records were included in the analyses.

Table 1. Effects of some production and environmental parameters on the preweaning performance of Yankasa sheep.

Table 2. Comparison of estimates of preweaning and weaning performance of Yankasa sheep by different investigators.

Trait

No. of observations

Mean ± SE

Investigators

Birth weight (kg)

214

2.80 ± 0.19

Adu et al (1979)


43

2.54

Adu and Buvanendran (1982)


357

2.51 ± 0.03

Hassan (1987)


2020

2.51 ± 0.01

Current study

Weaning weight (kg)

32

9.14.

Adu and Buvanendran (1982)


298

10.90 ± 0.19

Hassan (1987)


1203

10.87 ± 0.08

Current study

Preweaning ADG (g/day)

214?

107.8

Adu et al (1979)


32

75.8

Adu and Buvanendran (1982)


1203

91.86 ± 0.91

Current study

Weaning rate (%)

43

76

Adu and Buvanendran (1982)


362

85

Taiwo and Buvanendran (1983)


1576

77.9 ± 1.0

Current study

Environmental effects on the preweaning traits were examined by least squares analyses (SYSTAT, 1989) according to the linear model:

Yijklmn = u + Pi + Lj + Sk + Ml + Ym + Eijklmn

where Yijklmn was the preweaning trait (BOO, WW, ADG or WR) of an individual lamb, u was the overall mean, Pi was the fixed effect of the ith parity, Lj that of the jth litter size, Sk that of the kth sex, Ml that of the 1th month of birth, Ym that of the mth year of birth and Eijklmn was the random error term associated with each record.

Results and discussion

Birth weight

The least squares mean for BW (Table 1) agreed closely with earlier reports (Adu and Buvanendran, 1982; Hassan, 1987) but is lower than the estimate by Adu et al (1979), as shown in Table 2.

The effects of dam parity and litter size, sex, month and year of birth of lambs on BW were all highly significant (P<0.001). BW tended to increase with parity, with the highest BW occurring at the 6th parity. As expected, singles and male lambs weighed more at birth than their twins and female counterparts. BW was higher in June-November than in Dec-May. BW followed the seasonal fluctuation in forage availability. Yearly variations in BW did not follow any particular pattern except for a consistent improvement over the last three years of the study.

Weaning weight (Table 1)

The 90-day WW for Yankasa sheep in this study agreed closely with that reported by Hassan (1987) (Table 2) but both are higher than the earlier estimate by Adu and Buvanendran (1982). The effects of parity, litter size, sex, month and year of birth were highly significant (P<0.001).

WW increased consistently from first to fifth parity, and both singles and male lambs had a higher WW than twins and female lambs. WW of lambs born between November and March and also in June were below average, with lambs born in July having the highest WW. This pattern reflects the seasonal availability of forage, except for June. The low WW of lambs born in June could be due to a high disease incidence during this month; June also had the highest preweaning mortality rate. This observation needs closer clinical investigation to determine the cause. Yearly variations followed no particular pattern except for the consistent improvement in WW in the last four years of the study.

Preweaning ADG (Table 1)

The preweaning ADG obtained in this study is intermediate between values reported by Adu et al (1979) and Adu and Buvanendran (1982). The effects of parity, litter size, sex, month and year of birth on ADG were highly significant (P<0.001). ADG improved consistently from first to fourth parity. Singles and male lambs had a higher ADG than twins and female lambs. Below average ADG were obtained in June and between November and February. Yearly variations in ADG followed no pattern except for a consistent increase over the last four years of the study.

Weaning rate (Table 1)

The WR obtained in the present study compares favourably with that of Adu and Buvanendran (1985) but is lower than the figure reported by Taiwo and Buvanendran (1985) (Table 2). WR was significantly affected by litter size, month and year of birth (all P<0.001) and parity (P<0.01), but not by sex (P>0.05). WR increased consistently from first to fifth parity, with higher parities giving below average values. Single lambs had a higher WR than twin lambs. Lower WR values were obtained for lambs born between November and May. There is a close parallel between WR and rainfall pattern; lambs survive better if born in the dry rather than the wet months.

Conclusion

This study shows that there may be no advantage in keeping Yankasa breeding ewes under semi-intensive management beyond the sixth parity in terms of preweaning traits, especially WR which consistently fell below average in the latter group. However, the high parities had a relatively low number of observations and therefore need further study when larger data sets become available. The reasons for the peculiarly bad growth and weaning rate performances of lambs born in June also need further investigation. Seasonal effects on preweaning traits show that growth traits were better for lambs born in the wet seasons rather than the dry seasons, while the reverse was true of the weaning rate.

Acknowledgements

The authors are grateful to field staff of the Small Ruminant Research Programme, NAPRI, for the general assistance with this project and to the Federal Directorate of Food, Roads and Rural Infrastructure for funding support. The permission of the Director of NAPRI to publish this paper is gratefully acknowledged.

References

Adu I F and Buvanendran V. 1982. Preweaning performance of lambs from pure and crossbred matings among Nigerian breeds of sheep. World Review of Animal Production 18:73-77.

Adu I F, Brinckman W L and Kuteyi I S. 1979. Reproductive performance of indigenous sheep and their crosses. Nigerian Journal of Animal Production 6:38-40.

FDLPCS (Federal Department of Livestock and Pest Control Services). 1991. Nigerian national livestock survey. Volume 2. FDLPCS, Abuja, Nigeria. 289 pp.

Hassan W B. 1987. Genetic and environmental effects on the growth rate of Yankasa lambs. MSc thesis, Ahmadu Bello University, Zaria, Nigeria.

Osinowo O A. 1982. Oestrus synchronization, artificial insemination and early rebreeding in Yankasa sheep. Nigerian Journal of Animal Production 9: 107-111.

Osinowo O A. 1992. Problems and prospects for the development of small ruminants in Nigeria. In: The Nigerian livestock industry: Problems and prospects. Proceedings of a workshop held at Abuja, Nigeria, 26-27 February 1992, FDLPCS (Federal Department of Livestock and Pest Control Services), Abuja, Nigeria.

Osinowo O A and Ekpe G A. 1985. Post-partum intervals to oestrus and conception in Yankasa sheep. Journal of Agricultural Science 104:253-255.

SYSTAT. 1989. SYSTAT Version 4.1. SYSTAT, Inc., Evanston, Illinois, USA.

Taiwo B B A and Buvanendran V. 1983. Breed and environmental factors that influence lamb loss in Shika. NAPRI (National Animal Production Research Institute) Seminars 5:1-13. NAPRI, Zaria, Nigeria

Terrill C E. 1966. Genetic improvement in sheep and goats. In: Cole H H (ed), Introduction to livestock production. 2nd edition. W H Freeman and Co., San Francisco, USA. pp. 301-309.


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