REPRODUCTIVE PERFORMANCE OF HORMONALLY TREATED SHEEP MAINTAINED YEAR-ROUND IN A CONTROLLED-LIGHT ENVIRONMENT

Abstract

Six experiments were conducted on hormonally treated ewes maintained year-round in a controlled-light environment in a breeding program designed to produce three lamb crops in 2 yr. Various combinations of fluorogestone acetate (FGA), prostaglandin F2α (PGF2α) and pregnant mares' serum gonadotrophin (PMSG) were used to synchronize estrus in the ewes. There were no significant differences (P > 0.05) in fertility between FGA- and PGF2α-treated ewes when the ewes were having cyclic ovarian activity (cycling) at the time of treatment, i.e. in January and May in our system. Among ewes in the constant day-length lighting regime, fertility was lower in September than in January or May. Prolificacy ranged from 1.7 to 2.0 in the six experiments. Fecundity, a measure of the overall productivity, followed a similar pattern to fertility and was not significantly (P > 0.05) affected by the various treatments. These findings demonstrated the feasibility of maintaining a controlled 8-mo breeding program for sheep maintained year-round in a controlled-light environment. Key words: Reproduction in sheep, controlled light, hormone treatment effects.