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Kwame Nkrumah University of Science and Technology (2014)

Reproductive performance of Djallonké sheep in the Northern Region of Ghana

Sadat, Salifu

Titre : Reproductive performance of Djallonké sheep in the Northern Region of Ghana

Auteur : Sadat, Salifu

Université de soutenance : Kwame Nkrumah University of Science and Technology

Grade : Master of Philosophy (Reproductive Physiology) , 2014

his study was undertaken to assess the reproductive performance of Djallonké ewes in the Northern Region of Ghana. The study was in two parts. In the first part, blood progesterone levels of 20 Djallonké gimmers and 20 postpartum Djallonké ewes at the Pong Tamale Livestock Breeding Station in the Savelugu district of the Northern Region, were monitored to determine the age at puberty of the gimmers and the length of postpartum return to oestrus of the postpartum ewes (as evidenced by progesterone rises above 1ng/ml). The mean age and weight of the experimental gimmers was 136±3.38 days and 9.94±0.33kg, respectively at the beginning of the experiment. The postpartum ewes weighed 22.57±0.68kg at the start of sampling. Data on weight changes, body condition scores, blood glucose levels and packed cell volume (PCV) were also taken. Reproductive parameters such as age at first oestrus, age at first parturition of gimmers, lambing intervals of postpartum ewes, prolificacy and birth weights of lambs were also determined. The effect of season on all parameters was assessed. In the second part of the study, data from production records of two government sheep farms (Savelugu Sheep farm and CSIR-ARI sheep farm) and one private farm (Akana Farms) were analyzed to determine fertility rate, age at first parturition, lambing intervals, birth weight of lambs, prolificacy, pre-weaning mortality rates and the effect of season, parity of dam and location on these parameters. The results of the progesterone monitoring study showed that Djallonké gimmers reached puberty at a mean age of 220.6 days, with rainy season born gimmers reaching puberty at a significantly younger age (202.4 days vs. 238.7 days) (P<0.05). The gimmers of both seasons however showed their first progesterone rise at a similar weight (13.05kg for rainy season and 12.65kg for dry season gimmers) (P>0.05). vi Mean age and mean weight at first oestrus were 289.3 days and 15.65kg respectively. There were no differences in mean age and mean weight at first oestrus between seasons (P>0.05). Gimmers in the progesterone-monitoring study gave birth to their first lambs at the mean age of 460 days, with rainy season born gimmers lambing significantly earlier than the dry season born gimmers (424.6 vs. 495.8) (P<0.05). The progesterone patterns of gimmers showed a brief first rise of progesterone followed by a few irregular cycles before conception. Fifty-eight percent of the gimmers conceived when mated at the first display of overt oestrus, 95% conceived at the second and 100% conceived at the third oestrus. The postpartum ewes experienced first progesterone rise 69 days postpartum and came into overt oestrus 108 days postpartum. There was no significant difference between seasons for days to first rise of progesterone postpartum and days to first oestrus (P>0.05). The mean number of days from parturition to first oestrus was 101 days for rainy season ewes and 114 days for dry season ewes. The lambing intervals averaged 266.7 days for both seasons, with rainy season ewes having a mean lambing interval of 264.2 days while dry season ewes had a mean lambing interval of 268.7 days. There was no statistically significant difference between seasons for the lambing interval (P>0.05). Mean birth weight of lambs was 2.04kg, with the lambs of the rainy season ewes being significantly heavier (2.32kg vs. 1.83kg) and having higher placenta weights (175.2g vs. 132.7g) compared to the dry season ewes (P<0.05). The analyzed data from the 3 sheep farms, in the second part of this study, showed that average fertility rate was 85% for Akana Farms and 52% for Savelugu Sheep farm. The mean age at first parturition was 595 days. There was no significant difference in age at first parturition for rainy season and dry season born ewes (566 vs. 614 days) (P>0.05). The CSIR-ARI sheep had their first lambs at a significantly vii younger age (496 days) compared to the Akana Farms and Savelugu farm sheep (600 and 671 days respectively)(P<0.05). The overall mean lambing interval for sheep at the three stations was 267.4 days. Lambing intervals declined significantly with increasing parity (P<0.05). Mean lambing intervals were lowest for CSIR-ARI farm, followed by Akana farms and Savelugu farm (P<0.05). Mean birth weight for all stations was 2.57kg. Birth weight increased significantly with increasing parity (P<0.05) and rainy season born lambs were significantly heavier than dry season born lambs. Litter size and location also had a significant effect on the birth weight of lambs. Lambs born as twins had lower birth weights compared to lambs born as singles (2.25kg vs. 2.53kg) (P<0.05). Lambs born on Akana farms had the highest mean weights (2.67kg) followed by Savelugu farm (2.03kg) and lastly CSIR-ARI farm (1.59kg). The sex of the lamb did not significantly influence the birth weight of lambs. Overall pre-weaning lamb mortality was 28%. More of the dry season born lambs died before weaning compared to rainy season born lambs (36.3% vs. 16.7%) (P<0.01). Type of birth and sex of lamb did not significantly influence the pre-weaning mortality rate. The annual reproductive rate was 1.03 lambs per ewe of reproductive age. Based on this study, it was concluded that Djallonké gimmers reach puberty when they are 7 months old and are first mated when they are 8 months old. Gimmers born in the rainy season reach puberty earlier than the dry season born gimmers. Postpartum ewes resume cycling about 2 months postpartum and come into overt oestrus almost 4 months after parturition. Reproductive parameters for Djallonké females lambing in the rainy season are generally better than for those that lamb in the dry season.


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