Seasonal variation of reproductive performance, foetal development and progesterone concentrations of sheep in the subtropics.

The aim of the present study was to investigate the effect of breeding season [late spring (LSP) vs winter (WIN)] on reproductive performances, foetal development and progesterone (P(4)) concentrations of sheep in the subtropics. Ewes of Farafra breed were exposed for mating in LSP (n = 79) and WIN (n = 45). Ultrasonographic examinations were performed at days 25, 45 and 75 of mating to estimate the pregnancy rate, incidence of twinning and percentage of foetal losses. Foetal growth rate was determined at 10-day interval, and blood samples were taken on days 0 (oestrus), 8, 18 of oestrous cycle and on days 30, 45, 60 and 90 of pregnancy for P(4) analysis. The results showed that pregnancy and lambing rates were greater (p < 0.01) for ewes mated in LSP (93.7% and 92.4%) than for those mated in WIN (75.6% and 71.1%), respectively. There was no effect of season on the incidence of twinning (overall 19.1%) or the frequency of foetal losses (overall 7.3%). Transient reduction of placental size, foetal growth and P(4) concentration was observed following LSP matings. In conclusion, pregnancy and lambing rates were higher following LSP matings. Summer heat stress of the late spring mated ewes transiently interferes with foetal growth and P(4) concentrations.