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Evidence from several studies has supported a predictive relationship between measures of somatotropic hormones and genetically determined growth potential in domestic ruminants. In these studies, blood concentrations of hormones associated with growth were generally higher in lines or breeds with greater growth potential. However, no significant positive correlations between measures of hormone secretion and measures of growth in individual animals were observed.
The present study further assesses the association between growth potential, growth rate, and secretion of growth hormone (GH), prolactin (PRL), and thyrotropin (TSH) using bulls of two Hereford lines that differ in growth rate as a result of genetic selection. The objectives of this study were (1)to compare blood levels of GH, PRL, and TSH between the two lines of bulls, and (2) to evaluate the predictive value of sire hormone data for growth rate of their progeny.