Photoperiodism in the ewe: 4. A note on the effect on onset of oestrus in Clun Forest ewes of applying the same decrease in daylength at two different times of the year

Abstract

SUMMARYExperiments were carried out with Clun Forest ewes to determine the effect on the onset of oestrus of applying the same abrupt decrease in daylength at two different times of the year. An abrupt decrease in daylength of 3·75 hr was applied to the ewes on 1 July 1968 and on 24 April 1969. The mean number of days from the commencement of the light treatment to the onset of oestrous activity was 59·5 and 87·0 days, respectively. It is concluded that the time of year at which the light treatments were applied, or the previous light treatment of the Clun Forest ewes, or both, significantly (P<0·001) affected the date of onset of oestrus.