Using GNRH for improving ovarian activity and fertility of ewes during breeding season
2010
El-Harairy, M.A. | Ashmawy, T.A.M. | Abdel-Salam, O.M.
The present study aimed to increase lamb production per ewe per year through increasing number of lambing per year by studying the effect of GnRH treatment on 12 days post-partum on ovarian activity and lambing rate (1. t experiment) or 12 days post-mating on fertility of ewes (2. d experiment) during the breeding season. Ewes in both experiments were divided into two similar groups (10 ewes in each). The 1. t group represented the control group (G1), which were allowed for natural mating without hormonal treatment and ewes in the 2. d one were i.m. injected on day 12 postpartum (1. t experiment) or day 12 post-mating (2. d experiment) with 1 ml GnRH analogue (Receptal). Results show that GnRH treatment of ewes on day 12 postpartum (1. t experiment) markedly increased estrous rate to 100% and decreased postpartum period (1. t estrus interval) to 22 days as compared to 90% and 30 days for the control group. Mating period reduced to 10.25 d in treated group (13/Nov. to 05/Dec.) vs. 15.33 d in the control group (20/Nov, to 21/Dec.) Based on total number of treated ewes, lambing rate increased to 100% as compared to 80% in the control group, respectively. Sex ratio was significantly (P0.05) different between both groups. The control group yielded 70% male and 30% female lambs, versus 50% male and 50% female lambs in the treated group. Moreover, male or female lambs were heavier (P0.05) in the control than in the treated group. In the 2. d experiment, GnRH treatment of ewes on day 12 post-first mating increased lambing rate to 80% and litter size (P0.05) to 1.62 as compared to 70% and 1.14 in the control group, respectively. In conclusion, the administration of exogenous GnRH 12 days postpartum or 12 days after mating could increase lambing rate and fertility of ewes during breeding season.
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