Plasma Growth Hormone, Prolactin and Thyrotropin Secretory Patterns in Hereford and Simmental Calves

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Abstract
An experiment was conducted to test the hypothesis that bull calves of a larger, faster growing breed of cattle exhibit greater secretory activity of anabolic pituitary hormones than bull calves of a smaller, slower growing breed. Calves of both breeds were raised under similar conditions and maintained on the same diet for approximately 4 weeks before the blood sampling period. Simmental bull calves had higher (P<.01) average daily gains and a heavier (P<.01) mean body weight than Hereford bull calves. Overall plasma growth hormone (GH) concentrations were higher (P<.01) in Simmental bull calves than in Hereford bull calves. Mean baseline GH was also higher (P<.05) in Simmentals. Overall and baseline concentrations of prolactin (PRL) were similar for both breeds. Mean amplitude of PRL secretory spikes was higher (P<.05) for Simmental than for Hereford bull calves. There was no breed effect on any variable of thyrotropin secretion. These data suggest that representatives of a larger, faster growing breed of cattle (Simmental) exhibit greater secretory activity of GH and PRL than do representatives of a smaller, slower growing breed (Hereford). Copyright © 1981. American Society of Animal Science. Copyright 1981 by American Society of Animal Science.

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