Effect of light on spring breeding of mutton merino ewes

Abstract

SUMMARY Mutton Merino ewes, all of which had lambed in the preceding in-season, were divided into two groups some 30 days after lambing. The ‘light’ group was subjected, over 84 days, to a simulated decrease in daylength, achieved by first adding artificial light to the daylight and then stepping down the light at weekly intervals, from approximately 17 h, on 22 January, to natural daylength (13 ¾ h), on 20 April 1967. The control group was exposed to the normally increasing daylength. Starting on 1 March, the ewes in both groups were ‘teased’ and hand-service commenced on 20 April. The breeding activity (oestrus, ewes lambing, lambs born and twin births) as well as the length of gestation and birth weight appeared to be unaffected by the light. It would appear that the ‘short-day’ photoperiodic theory is not applicable to all breeds of sheep, and it is suggested that in sheep with a long sexual season genetic heterozygosity may be responsible for regulating the breeding season by allowing other environmental stimuli, besides light, to trigger-off sexual activity.