MAINTENANCE OF CORPORA LUTEA IN SHEEP WITH LACTOGENIC HORMONE

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Abstract
SUMMARY: Prolactin given to sheep has a luteotrophic effect. In anoestrous ewes, in which ovulations were caused by pregnant mares' serum (PMS) injections, the majority of corpora lutea were maintained in a functional state for 20 and 30 days with daily prolactin treatment. In the absence of prolactin, corpora lutea degenerated rapidly and completely. Prolactin injected into ewes with freshly ovulated follicles, beginning with the 2nd day of the cycle, caused cycles to be prolonged to about 26 days in five out of ten ewes. Ovulation was suppressed during this time. In the remaining five ewes prolactin had no effect, and neither heat nor ovulation was postponed. In anoestrous ewes prolactin caused the larger follicles present in the ovaries to be heavily luteinized. By contrast, follicles of ewes treated with prolactin during the breeding season were not luteinized. The reason for this difference in response is not known.