Ovulation rate and oocyte numbers in ewes after prolonged exposure to oestrogenic pasture

Adams, N. R.; Oldham, C.M.; Heydon, R. A.

doi:10.1530/jrf.0.0550087

Cited by 8 publications

(3 citation statements)

References 11 publications

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“…The increased LH would stimulate the ovary to secrete more Ez and eventually a new dynamic equilibrium would be set in which higher plasma levels of gonadotrophins and E z were produced. Elevation in gonadotrophin levels would stimulate follicular development, and in support of this Adams et al (1979) have observed higher ovulation rates in ewes that became infertile after grazing oestrogenic clover.…”

Section: Introductionmentioning

confidence: 76%

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Rodgers

Clarke

Findlay

et al. 1980

Aust. Jnl. Of Bio. Sci.

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The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock I, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml-1 x 1 h) was significantly (P < 0'05) greater in clover-infertile ewes (10'4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5·4 area units). Tonic LH and FSH secretions during the breeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0'05) elevated in clover-infertile ewes (10' 9 area units) compared to normal ewes (5' 4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7. 8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 P (Ez) during the breeding season were similar in the three groups.In another experiment, the positive feedback release of LH following administration of Ez (12'5,25 or 50 f.1g per ewe) was measured in anoestrous ewes of flock 2. Significantly (P < 0·01) more clover-infertile ewes demonstrated a positive feedback effect than control ewes when given 12· 5 f.1g Ez but not when given higher doses.The elevation of LH secretion in permanently affected clover-infertile ewes is consistent with the hypothesis that the hypothalamo-pituitary axis of these ewes is less responsive to the negative feedback effect of oestrogen. Furthermore, the patency of the positive feedback loop is consistent with the ability to ovulate.Other keywords: Clover disease. IntroductionLong-term grazing of oestrogenic clover pastures may cause permanent infertility in ewes (Bennetts et al. 1946;Barrett et al. 1965) although not all ewes grazing oestrogenic clover exhibit infertility. Infertile ewes have uterine endometrial hyperplasia and changes in cell type and function of the cervix (Adams 1976). In addition, there may be an associated neuroendocrine lesion. For example, Findlay et al. (1973) have reported that when infertile ewes which had previously grazed oestrogenic clover were ovariectomized, they were less likely to show elevated plasma LH levels, i.e. positive feedback (Goding et al. 1969), in response to oestradiol-17f1 (E 2 ) treatment than were normal ovariectomized ewes. This reduced responsiveness of the hypothalamo-pituitary axis to E2 could be related to changes in the number or affinity

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Section: Introductionmentioning

confidence: 76%

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Rodgers

Clarke

Findlay

et al. 1980

Aust. Jnl. Of Bio. Sci.

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“…Laparoscopy was the most common method used to assess whether ovulation had occurred [one outcome per study, with the exceptionof Smith et al ( 114 )]. Four of the studies were conducted in sheep, three of which were conducted in Western Australia ( 7 , 114 , 149 ) and the fourth in Egypt ( 150 ). There was no bias across the included studies (P = 0.8349, Figure 2 ).…”

Section: Resultsmentioning

confidence: 99%

Estrogenic Pastures: A Source of Endocrine Disruption in Sheep Reproduction

et al. 2022

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Phytoestrogens can impact on reproductive health due to their structural similarity to estradiol. Initially identified in sheep consuming estrogenic pasture, phytoestrogens are known to influence reproductive capacity in numerous species. Estrogenic pastures continue to persist in sheep production systems, yet there has been little headway in our understanding of the underlying mechanisms that link phytoestrogens with compromised reproduction in sheep. Here we review the known and postulated actions of phytoestrogens on reproduction, with particular focus on competitive binding with nuclear and non-nuclear estrogen receptors, modifications to the epigenome, and the downstream impacts on normal physiological function. The review examines the evidence that phytoestrogens cause reproductive dysfunction in both the sexes, and that outcomes depend on the developmental period when an individual is exposed to phytoestrogen.

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“…The duration of oestrous behaviour was not altered in clover-affected ewes (Smith, 1971;Lightfoot et al, 1974). The ovulation rate is slightly higher in clover-affected ewes (Adams, Oldham & Heydon, 1979), and because an increased ovulation rate is generally accompanied by a greater production of oestrogen (Wheeler, Baird, Land & Scaramuzzi, 1977) this may be reflected in a slight increase in the amount of oestrogen circulating in such ewes, although there are no differences in ovarian vein concentrations of oestrogens in affected and control ewes (Rodgers et al, 1980). Taken altogether, the evidence suggests there may be a slight increase in the amount of endogenous oestrogen in affected ewes, but it appears insufficient to cause the large changes seen in cervical mucus (Lindsay & Francis, 1969).…”

Section: Oestrogenmentioning

confidence: 99%

A changed responsiveness to oestrogen in ewes with clover disease

Adams¹

2019

Proc

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When clover-infertile ewes are subsequently exposed to non-oestrogenic pasture, they have a reduced fertilization rate, due to an inability to store spermatozoa in the cervix, and the cervical mucus has a reduced spinnbarkeit, caused by a slower response to oestrogenic stimulation. Vaginal cell keratinization and oestrous behaviour occurred more slowly after treatment of affected ewes with oestrogen. Other changes in affected ewes suggest that phyto-oestrogens have permanent mild differentiating effects on adults. Sexual behaviour is masculinized, the cervix takes on a uterine-like appearance and the genital tract becomes permanently oestrogenized. The manner in which these changes relate to the altered responsiveness to oestrogen remains to be clarified.

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Ovulation rate and oocyte numbers in ewes after prolonged exposure to oestrogenic pasture

Abstract: Ewes which had been exposed to oestrogenic clover for 3 years showed an elevated ovulation rate but no difference in numbers of primordial follicles compared with normal ewes.

Cited by 8 publications

References 11 publications

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Estrogenic Pastures: A Source of Endocrine Disruption in Sheep Reproduction

A changed responsiveness to oestrogen in ewes with clover disease

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