Estrus response and fertility of Menz and crossbred ewes to single prostaglandin injection protocol.

Natural lambing in sheep in Ethiopia occurs throughout the year in a scattered manner negatively affecting survival and growth rates of the lambs born during the unfavorable season of the year. Thus, controlling the time of mating artificially using exogenous source of hormones is considered as one of the ways to mitigated problems related to haphazard lambing. To this end, an experiment was conducted to evaluate efficacy of prostaglandin-based estrus synchronization protocol in local and crossbred ewes. A total of 160 ewes (80 local and 80 crossbreds) which lambed at least once and aged 3-5 years were used. Lutalyse® (dinoprost tromethamine sterile solution equivalent to 5 mg dinoprost per ml) and its analog, Synchromate® (cloprostenol sodium equivalent to 0.250 mg cloprostenol per ml), were tested at different doses. The treatments used were intramuscular injection of (1) 2.50 ml of Lutalyse® (12.5 mg dinoprost tromethamine), (2) 2 ml of Lutalyse® (10.0 mg dinoprost tromethamine), (3) 1 ml of Synchromate® (0.25 mg of cloprostenol Sodium), and (4) 0.8 ml of Synchromate® (0.20 mg of cloprostenol Sodium). Forty ewes (20 local and 20 crossbreds) were allocated per treatment. Following injection of the respective hormones, rams of known fertility were introduced into the flock for the duration of 96 h at the ratio of one ram to 10 ewes. All estrus synchronization protocols except treatment 4 (0.8 ml of Synchromate®) induced estrus (heat) in majority (55-65%) of local and crossbred ewes within 96 h post-hormone injection. The time interval from hormone administration to onset of estrus was also more or less similar for all treatment groups except for treatment group 4 which showed heat quicker. The highest lambing rate was recorded in local ewes (84.62% (11/13) treated with 2.5 ml of Lutalyse®, whereas the least was obtained in crossbreds (33.33% (3/9) treated with 0.8 ml Synchromate®. In conclusion, even though 2.5 ml and 2 ml of Lutalyse® or 1 ml of Synchromate® were able to induce heat in majority of local and crossbred ewes, the highest lambing percentage was obtained from ewes treated with 2.5 ml of Lutalyse®. Therefore, the use of 2.5 ml Lutalyse® is recommended to synchronize estrus in local and crossbred ewes under Ethiopian smallholder sheep production system for the benefit of improved lambing rate.