Daylengths of 13 or 20 hr were applied to six groups of nine ewes during the 2nd to 8th, 8th to 14th and 14th to 20th week of pregnancy. Two groups of nine non-pregnant ewes received a constant 13- or 20-hr daylength during the above experimental period. A group of 10 non-pregnant ewes which initially received a 20-hr daylength were subjected to a 13-hr daylength in the last 14 to 20 weeks of the experimental period. After parturition (26 March) all the ewes received increasing natural daylength.
The mean number of days from the onset of the experimental light treatments (17 November) to the cessation of oestrous activity did not vary significantly between the three non-pregnant groups of ewes and was on average 89 days.
Only two of the 82 ewes, both non-pregnant, exhibited oestrus prior to the longest day (22 June). The various light treatments did not significantly affect the mean dates of occurrence of the natural breeding season of the groups of ewes.