Studies of pituitary function in lactating ewes

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Abstract
The release of LH [luteinizing hormone] from the pituitary of lactating ewes was studied. In Exp. [experiment] 1, ewes were injected with 50 .mu.g estradiol benzoate (OB), 2.0 mg testosterone propionate (TP) or oil only (control) on days 5, 10 or 20 after lambing. LH was measured in peripheral plasma samples obtained 20-38 h after treatment, and ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between days 5-20 after OB treatment but increased after TP treatment. The releases of LH were not always accompanied by ovulation, and the incidence of ovulation was higher in ewes treated with TP. In Exp. 2, lactating ewes were injected with 1 or 5 (at 2 h intervals) doses of 50 .mu.g Gn-RH [gonadotropin releasing hormone], on days 12 or 25 after lambing. LH was measured in peripheral plasma samples collected every 2 h for 10 h and every 3 h for a further 70 h. Release of LH occurred in all ewes, the amount being greater in ewes receiving multiple injections and in ewes treated on day 25. The incidence of ovulation was higher after treatment on day 25. Multiple injections of Gn-RH appeared to reduce the incidence of abnormal corpora lutea.