Programmed year-round sheep breeding

Abstract

A program of controlled year-round sheep breeding, designed to provide batch lambing every 2 months, was evaluated on a private property in the Central Tablelands of New South Wales, over a 16-month mating period commencing in October 1977. It was preceded by a preliminary test designed to evaluate the use of pregnant mare serum gonadotrophin (PMSG) in conjunction with intravaginal progestagen sponges in the breeding season, and the importance of mating strategy. A flock of 140 Border Leicester x Merino ewes-of which 132 survived to the end of the test (mean 136)-and 6 Poll Dorset rams were used. Mating, pregnancy diagnosis and lambing were scheduled in advance using synchronization and induction of oestrus with intravaginal (i/v) progestagen sponges and PMSG (400 or 600 i.u.), pregnancy diagnosis based on plasma progesterone assay at 18 days after mating, and induction of parturition with either dexamethazone (DM ; 16 mg) or oestradiol benzoate (ODB; 20 mg). Treatment of a batch of ewes commenced every 60 days, and ewes diagnosed non-pregnant from the previous batch were included. Synchronized oestrus was induced 90 days after lambing, immediately after which lambs were weaned. There were eight lambing batches involving 365 treatments, which resulted in 219 lambings (60%) and 346 lambs, of which 321 survived to 72 hours, an average of 27 lambings and 40 viable lambs/2 months. The annual production rate was 176 viable lambs per 100 ewes.