Effects of season, lactation and plane of nutrition on prolactin concentrations in ovine plasma and the role of prolactin in the control of ewe fertility

Rhind, S. M.; Robinson, John J.; Chesworth, J. M.; Crofts, R. M. J.

doi:10.1530/jrf.0.0580145

Cited by 23 publications

(7 citation statements)

References 17 publications

(25 reference statements)

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“…In support of previous work by Walton et al (1977) and Rhind, Robinson, Chesworth & Crofts (1980), the breeding season was characterized by low or basal levels of prolactin whereas these became elevated during seasonal anoestrus. However, because of the difference in the onset of the breeding season between the two breeds, the levels of prolactin encountered during the transition to reproductive activity were much higher for the Dorset Horn ewes.…”

Section: Discussionsupporting

confidence: 86%

Seasonal changes in LH and prolactin concentrations in ewes of two breeds

Webster¹,

Haresign²

1983

Reproduction

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The current experiment was designed to investigate whether changes in prolactin concentrations might be involved in the seasonal change in responsiveness of the hypothalamic-pituitary axis to the negative feedback effects of oestradiol in the ewe. Twelve Dorset Horn ewes (long breeding season) and 12 Welsh Mountain ewes (short breeding season) were ovariectomized after insertion of empty subcutaneous implants (N = 2 per breed), or ones containing oestradiol-17 beta (N = 10 per breed). Intact ewes, 10 of each breed, were used to monitor breeding activity. Mean weekly plasma LH concentrations in oestrogen-treated ovariectomized ewes of both breeds were elevated over the period corresponding to their respective breeding seasons, but were basal during anoestrus. The changes in prolactin concentrations, however, followed the same temporal pattern in both breeds and were approximately parallel to changes in daylength. These data support the suggestion of a seasonal change in negative feedback responses to oestradiol which corresponds to changes in breeding activity, but any involvement of prolactin in this response remains questionable.

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Section: Discussionsupporting

confidence: 86%

Seasonal changes in LH and prolactin concentrations in ewes of two breeds

Webster¹,

Haresign²

1983

Reproduction

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“…2, Groups 2 and 3), in which parturition occurred in the middle of the breeding season, had lower prolactin levels than did ewes which lambed towards the end of the breeding season. This observation supports previous studies demonstrating seasonal changes in prolactin secretion in lactating (Rhind, Robinson, Chesworth & Crofts, 1980) and non-lactating (Walton et al, 1977) ewes. In all likelihood these differences in prolactin secretion post partum could be accounted for by an effect of daylength.…”

Section: Discussionsupporting

confidence: 93%

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

Fitzgerald¹,

Cunningham²

1981

Reproduction

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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.

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“…This increase in pro¬ lactin secretion may be due to the change in photoperiod which is particularly marked at the end of the breeding season (Walton, McNeilly, McNeilly & Cunningham, 1977;Rhind, Robinson, Chesworth & Crofts, 1980;Worthy & Haresign, 1983). The diurnal pattern of plasma prolactin concentrations observed in both groups on day 1 of the luteal phase appears to be biphasic by days 6 and 10 with a daytime rise occurring in addition to the expected nocturnal rise.…”

Section: Discussionmentioning

confidence: 91%

Changes in FSH and the pulsatile secretion of LH during treatment of ewes with bovine follicular fluid throughout the luteal phase of the oestrous cycle

Wallace¹,

McNeilly²

1986

Journal of Endocrinology

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Treatment of Damline ewes with twice-daily i.v. injections of bovine follicular fluid during the luteal phase for 10 or 2 days before prostaglandin-induced luteolysis resulted in a delay in the onset of oestrous behaviour and a marginal increase in ovulation rate. During the treatment cycle, blood samples were withdrawn at 15-min intervals for 25 h from 08.00 h on days 1, 6 and 10 (day 0 = oestrus). At all three stages of the luteal phase, plasma FSH concentrations were suppressed relative to controls 3 h after the 09.00 h injection of follicular fluid and remained low until 06.00 h on the following day. In the 10-day treatment group LH pulse amplitude was significantly greater than that of controls on days 6 and 10. Pulse frequency remained high throughout treatment and was significantly higher relative to controls on day 10 despite normal progesterone levels. The results suggest that the higher pulsatile LH secretion during the luteal phase is due to reduced negative feedback effects of oestradiol occurring as a result of the follicular fluid-induced reduction in FSH.

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Effects of season, lactation and plane of nutrition on prolactin concentrations in ovine plasma and the role of prolactin in the control of ewe fertility

Cited by 23 publications

References 17 publications

Seasonal changes in LH and prolactin concentrations in ewes of two breeds

Seasonal changes in LH and prolactin concentrations in ewes of two breeds

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

Changes in FSH and the pulsatile secretion of LH during treatment of ewes with bovine follicular fluid throughout the luteal phase of the oestrous cycle

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