Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep

The efficacy of using a low cost system for delivering progesterone as part of an estrous synchronization protocol in sheep was evaluated. In experiment 1, Barbados Black Belly ewes (n = 34) and ewe lambs (n = 35; 37.5 ± 0.9 kg) were assigned to be untreated, control animals (C), or to receive PGF2α on d0 (PG), or receive two injections of progesterone (200 mg, i.m. each) on D −5 and on D −2.5, prior to PGF2α, on D 0 (2PPG). Treatment with 2PPG increased the proportion of animals lambing to the first service (P < 0.05), an effect that was greater in ewe lambs than ewes (treatment × parity; P < 0.05). The interval from ram introduction to lambing and the mean lambing day was less (P = 0.04) in the 2PPG-treated animals compared to control animals. In Experiment 2, lactating ewes from experiment 1 (n = 61) 60–85 days postpartum were assigned within parity and number of lambs reared to remain nursing (S; n = 29) or weaned (W; n = 32) 3 weeks prior to treatment with the 2PPG protocol. There was no effect of treatment on the proportion of animals lambing to the first service or overall, interval from ram introduction to lambing and lambing interval. An 8-month lambing interval was observed in ewes in which estrus was synchronized regardless of physiological state. In conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus to reduce the lambing interval and maximize productivity in tropical breeds of sheep.