Infertility in Ewes caused by Prolonged Grazing on Oestrogenic Pastures: Oestrus, Fertilization and Cervical Mucus

Abstract

An experiment was conducted to investigate oestrus, fertilization and cervical mucus production in two groups of ewes, one group being of reduced fertility due to prolonged grazing on oestrogenic subterranean clover. Ewes within each of the oestrogenic (Yarloop subterranean clover) and control (Mt Barker subterranean clover) treatments were divided into subgroups of 'high' and 'low' fertility on the basis of total lambs born over the preceding 3 years.The results confirmed previous findings concerning a failure of sperm transport and reduced fertilization in affected ewes but the duration of oestrus (approx. 23 h) was normal. Ewes in the Yarloop treatment, and in particular those in the low-fertility subgroup, were found to produce significantly more cervical mucus than control ewes over the period -30 to + 30 h relative to time of onset of oestrus. This result is discussed in relation to the failure of sperm transport.

Effects of Oestradiol on Plasma Concentrations of Luteinizing Hormone in Ovariectomized Ewes with Clover Disease

“…Failure of positive feedback on LH is the primary cause of the permanent infertility in the 'androgenized' rat. In contrast, the entire clover-affected ewe can fully compensate for the defects in both behavioural responsiveness and the sensitivity of positive feedback, so that the duration of oestrus is normal in affected ewes (Lightfoot et al 1974) and the surge of LH occurs normally (Rodgers et al 1980;Charnley et al 1981). As discussed above, the method by which the entire ewe compensates is unclear.…”

Oestrogen Receptors and Metabolic Activity in the Genital Tract After Ovariectomy of Ewes With Permanent Infertility Caused by Exposure to Phyto-Oestrogens

“…This infertility, known as clover disease, is not simply a continuation of those responses which occur during treatment of an animal with oestrogen. Both the occurrence of oestrus and the ovulation rate are impaired in ewes grazing oestrogenic clover , but in permanently affected ewes oestrus and ovulation are relatively normal (Lightfoot, Smith, Cumming, Marshall, Wroth & Hearnshaw, 1974) and the infertility results from impaired sperm transport through the cervix (Lightfoot, Croker & Neil, 1967). This persistent effect of phyto-oestrogens on the cervix, which takes on a histological appearance more like the uterus (Adams, 1976), is not understood.…”

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

“…Although oestrogen is less efficient at releasing LH from the pituitary of affected ewes (Findlay et al, 1973), ovulation, which is dependent on a preceding LH peak, proceeds normally (Lightfoot et al, 1967(Lightfoot et al, , 1974. Furthermore, although the behavioural sensitivity to exogenous oestrogen is decreased in affected ewes (Adams, 1978), the duration of oestrous behaviour at natural oestrus is not diminished (Smith, 1971;Lightfoot et al, 1974). This circumstantial evidence, together with the elevation in ovulation rate, suggests that endogenous oestrogen production may be slightly increased in ewes with permanent phytooestrogenic infertility.…”

“…A slight elevation in levels of endogenous oestrogen may explain some apparently conflicting data on ewes with permanent phyto-oestrogenic infertility. Although oestrogen is less efficient at releasing LH from the pituitary of affected ewes (Findlay et al, 1973), ovulation, which is dependent on a preceding LH peak, proceeds normally (Lightfoot et al, 1967(Lightfoot et al, , 1974. Furthermore, although the behavioural sensitivity to exogenous oestrogen is decreased in affected ewes (Adams, 1978), the duration of oestrous behaviour at natural oestrus is not diminished (Smith, 1971;Lightfoot et al, 1974).…”