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

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Abstract
The effects of estradiol on plasma luteinizing hormone (LH) concentrations were examined in 15 ovariectomized control ewes and 15 similar ewes with permanent infertility after prolonged grazing on estrogenic clover pasture (clover disease). Before treatment, the plasma concentrations of LH were similar in the control and affected ewes. After i.v. injection with 40 .mu.g estradiol-17.beta. during the anestrous season, the decline in LH concentration was greater in the clover-affected ewes and the subsequent elevation above original baseline levels was smaller. After i.m. injection with 15 or 30 .mu.g estradiol benzoate during the normal breeding season, fewer clover-affected ewes showed a surge of LH, and the response was both reduced and retarded. This difference between the 2 groups was not observed in studies on intact ewes; in intact ewes the difference is probably masked by a greater tonic LH activity in affected ewes. The results of the present study are consistent with the hypothesis that prolonged exposure to estrogenic pasture has a differentiating, or androgenizing effect on the adult ewe.

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