Oestrogenic damage and reduced fertility in ewe flocks in south Western Australia

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Abstract
Prolonged exposure to oestrogen causes transsexual redifferentiation in the ewe, which can be assessed experimentally by measuring the cross-sectional area of lamina propria (lp) tissue lying underneath the cervical folds in the mid-cervix. The extent of transsexual redifferentiation caused by prolonged exposure to clover oestrogens was measured in ewes from 13 farms in Western Australia. Groups of 90-157 mature ewes were mated under normal farming husbandry, and consigned to the abattoirs 6-8 weeks later. Histological sections were prepared from the mid cervix of 37-80 ewes from each flock. The area of lp was increased in ewes from the three farms with a history of infertility due to oestrogenic clover, when compared with ewes from the four farms in non-clover areas. Overall, the mean area of lp in ewes from the 13 farms was correlated (r = 0.81, P < 0.01) with the proportion of non-pregnant ewes, but less so with the potential lambing rate as judged by the number of foetuses/100 ewes (r = -0.51, N.S.). This contrast came about because flocks affected by oestrogen-induced transdifferentiation also tended to have higher ovulation rates; a regression including both the ovulation rate and area of lp accounted for 89010 of the variation between flocks in potential lambing rate. It is concluded that clover oestrogens are an important cause of the relatively high proportion of ewes which fail to lamb in Western Australia.