Induction of lambing every eight months in two breeds of sheep by light control with or without hormonal treatment

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Abstract
SUMMARY Suffolk and Rambouillet female sheep (ewes) were kept in pens where daylight was gradually reduced and were treated, or not treated, with hormones to obtain four lambing cycles in 2·5 years. Oestrus in May, June and July was induced more easily (P<0·01) in Rambouillet than the Suffolk ewes. The advantage of higher conception rates in the Rambouillet ewes during anoestrus was offset by the higher prolificacy rates in the Suffolk in the other three lambing cycles. On average, each breed produced 128 lambs per 100 ewes exposed per lambing cycle. This corresponds to 5·1 lambs per ewe in four lambings, which is equivalent to 2·04 lambs per ewe per year. Under the conditions of the experiment, the addition of Syncro-Mate pessaries (20 mg fluorogestone acetate) and pregnant mare serum gonadotrophin (PMSG, 5 ml/ewe, 50 IU/ml) to the treatment of reduced daylight did not affect the ovulation or conception rates.

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