Oestrous and ovarian activity of subtropical fat-tailed Rahmani sheep and their response to light treatment

Abstract

SummaryOestrous and ovarian activity were studied throughout the year in 29 subtropical Rahmani ewes using both vasectomized rams and intravaginal electrical resistance measurements. Percentages of ewes in oestrus and of ewes ovulating were consistently high throughout the year with a detectable drop in spring months. The drop was more pronounced and lasted longer in oestrous activity than in ovarian activity. About 33% of the ewes showed continuous ovarian activity throughout the year while almost all ewes had periods of behavioural anoestrus.Effects of artificial light regimen on oestrous and ovarian activity were investigated in 21 Rahmani ewes over a 6-month period from January to June. Oestrous and ovarian activity were slightly lower in the light-treated (L) group than the control (C) group during the period of abrupt increase in daylength. With gradual decrease in daylength, the percentage of ewes showing oestrus was markedly higher in the L than in the C group (84·6 v.37·5% during May).It was concluded that daylength change, although limited in this region, is a main factor controlling the seasonal changes in oestrous and ovarian activity in subtropical Rahmani sheep.