Effect of removal of lambs or treatment with bromocriptine on plasma concentrations of prolactin and FSH during the post-partum period in ewes lambing at different times during the breeding season

Abstract

Daily determinations of FSH and prolactin in plasma were made for 10-12 weeks after parturition in ewes which lambed either in the middle of (December) or late in (February) the breeding season. Fluctuations in the plasma concentrations of FSH could not be related to the time after parturition or to the occurrence of otherwise of oestrus and ovulation. However, there was evidence of an increased secretion of prolactin post partum but only in those ewes which lambed in February. The lack of an elevated level of prolactin during the post-partum period in the December-lambing ewes was associated with an earlier return to oestrus by these animals. The suppression of prolactin concentrations by treatment with bromocriptine to undetectable values in the December-lambing ewes was not associated with an earlier return to oestrus. The removal of lambs at various times post partum from those ewes which lambed in February was not associated with any marked changes in prolactin secretion. The results suggest that when the plasma concentrations of prolactin are low post partum there is a greater likelihood of an earlier resumption of breeding activity in the ewe.

Evidence for direct inhibition of ovarian function by prolactin

“…A similar situation and sequence of events occurs during the re-establishment of ovarian cyclicity during lactation in the cow (e.g. Schams et al, 1978;Stevenson & Britt, 1979;Carruthers & Hafs, 1980;Webb, Lamming, Haynes & Foxcroft, 1980), sheep (Fitzgerald & Cunningham, 1981;Wright, Geytenbeck, Clarke & Findlay, 1981) and pig (Stevenson, Cox & Britt, 1981). Whether the high levels of prolactin or the suckling stimulus alone or together are responsible for the suppression of LH secretion during lactation has been discussed previously (McNeilly, 1980a).…”

Seasonal Endocrine Changes and Breeding Activity in Mediterranean Wild Ruminants

“…Female mouflons lambing in April show 1-2 cycles in May (Santiago-Moreno et al 2000a). As in other mammals, resumption of sexual activity after parturition is affected by body condition, suckling intensity and age (Fitzgerald and Cunningham 1981;Hulet et al 1986). Thus, in younger animals or mouflons with low body condition, the time elapsing from parturition to resumption of ovulatory activity is approximately 200 days, with their first ovulation occurring at the beginning of the next breeding season (October).…”

“…2000a). As in other mammals, resumption of sexual activity after parturition is affected by body condition, suckling intensity and age (Fitzgerald and Cunningham 1981; Hulet et al. 1986).…”

Effect of TRH on the secretion of prolactin in ewes at various stages of pregnancy and in non-pregnant ewes during the breeding season and seasonal anoestrus

“…Prolactin was measured with a specific double-antibody radioimmunoassay as described by Walton et al (1980) and slightly modified by Fitzgerald & Cunningham (1981). All samples from each animal were assayed at random in a single batch and the precision of the assays as reflected by the interand intra-assay coefficients of variation was always <10%.…”