Photoperiodism in the ewe: 2. The effects of various patterns of decreasing daylength on the onset of oestrus in clun forest ewes

Abstract

1970). Photoperiodism in the ewe: 2. The effects of various patterns of decreasing daylength on the onset of oestrus in clun forest ewes. SUMMARYIn six light-proofed buildings experiments were conducted with Clun Forest ewes to determine whether the date of first oestrus was affected by the absolute size of reduction in the case of an abrupt decrease in daylength and by the rate of reduction in the case of a given total decrease in daylength. The mean number of days from the onset of the light treatments to first oestrus (the reaction interval) for ewes receiving gradual decreases in daylength of 3-5, 7-2 or 10-9 min/day from 1 July were 66-4, 53-7 or 33-6 days, respectively. The reaction interval for ewes receiving abrupt decreases in daylength of 3-75, 7-75 or 11-75 hr on 1 July were 59-5, 44-8 or 33-6 days, respectively. A control group of ewes at pasture on natural daylength had a mean reaction interval of 66-2 days. It is concluded that the various light treatments applied significantly affected the date of onset of oestrus in Clun Forest ewes.

Abrupt decrease in daylength and short-term changes in the plasma concentrations of FSH, LH and prolactin in anoestrous ewes

“…This is consistent with earlier studies (Ducker et al, 1970;Walton et al, 1977), although a small part of the effect may have been due to the heavier bodyweight of the ewes on short days. There was an unusual degree of synchrony in the onset of oestrus in the ewes kept under natural daylength.…”

Seasonal changes in ovulatory activity, plasma prolactin, and melatonin concentrations, in Mouflon (Ovis gmelini musimon) and Manchega (Ovis aries) ewes

“…It has long been accepted that the photoperiod is the primary environmental cue controlling seasonal breeding in sheep [11,20,47]. The photoperiodic signal is transduced by the pineal gland into a pattern of melatonin secretion which, in turn, provides a critical endocrine signal to regulate secretion of other hormones involved in the onset and termination of the annual breeding season [4,16].…”

Short- and long-term effects of manipulation of the pineal/melatonin axis in ewes

“…Yeates (1949) and Hafez (1952) Thwaites and Bowman, 1970). These authors also found that various patterns of increasing daylength affected the onset of anoestrus (Ducker and Bowman, 1970a).…”