Two routes of oPRL supplementation were used to elevate peripheral or local concentrations of PRL in autumn-lambing ewes which, based on previous results, were expected to have low plasma PRL concentrations and milk yields relative to spring-lambing ewes. Administration of 10 mg oPRL directly into the gland or subcutaneous injection of 0.5 mg/kg oPRL did not increase the milk yields, or change the composition of milk, compared to controls. These results suggest that the circulating and intramammary concentrations of PRL in autumn-lambing ewes are not limiting lactogenesis. However, because the plasma prolactin concentration in the ewes was unexpectedly high, it was not possible to reach firm conclusions regarding possible effects of supplementary oPRL in ewes with naturally low plasma PRL concentrations. Nevertheless, the results indicate that raising the intramammary concentration of PRL around the time of parturition, in ewes with circulating PRL concentrations characteristic of normal spring-lambing ewes, does not enhance lactogenesis.
Proceedings of the New Zealand Society of Animal Production, Volume 54, , 115-118, 1994
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