Use of Active Immunization against Prolactin to Study the Influence of Prolactin on Growth and Reproduction in the Ram

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Abstract
An experiment was conducted to determine whether prolactin (PRL) is involved in the maintenance of reproductive tissue weights and body growth in yearling rams. Suppression of circulating PRL was achieved by active antibody production against bovine PRL. Free plasma PRL concentrations in immunized rams were decreased (P<.05) by 73% after 3 months of treatment and 91% after 10 months of treatment in relation to concentrations in control rams. Average daily gain and final body weight were lower (P<.05) for rams with suppressed circulating PRL (.042 kg/day and 67.0 kg for treatment rams and .060 kg/day and 72.7 kg for control rams). Although testes weights were 32% lower for the treated rams, antibody treatment did not affect (P>.05) the weights of the testes or accessory sex glands. No treatment effect was noted on plasma luteinizing hormone (LH), growth hormone (GH) or thyrotropin (TSH). Seasonal differences were observed in some variables of LH, GH and TSH secretion. Mean baseline LH for all animals was higher (P<.01) in December than in March, June or September. Overall and baseline concentrations of GH and TSH were highest (P<.01) in December. These data suggest that (1) PRL is involved in body growth of the yearling ram, and (2) PRL may have a role in the maintenance of reproductive tissue weights in the yearling ram. Copyright © 1981. American Society of Animal Science. Copyright 1981 by American Society of Animal Science.

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