Relationship of Growth Hormone, Prolactin and Thyrotropin Secretion to Individual and Progeny Performance of Hereford Bulls3

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Abstract
Six Hereford bulls from a line selected with an index of body weight and muscling score were compared with six bulls from a control line to determine if increased growth in the selected line was associated with changes in plasma levels of growth hormone (GH), prolactin (PRL) and(or) thyrotropin (TSH). The predictive value of sire hormone data for growth rate of progeny was also evaluated. Bulls of the index line were heavier at birth (P<.02) and had higher postweaning daily gains (P<.01) than bulls of the control line. Blood samples were collected from bulls (ages 2 and 3 yr) at 15-min intervals for 8 h. Overall plasma GH concentrations were higher (P<.03) in the index bulls than those in the control line. All characteristics of PRL secretion examined tended to be higher in the index bulls, but only mean overall and baseline differences approached significance (P<.10). There were no significant differences in measures of TSH secretion between lines. Sire differences in hormone characteristics accounted for significant amounts of variation in birth weight and postweaning gain of progeny, but not in gain to weaning. Also, when considered jointly, hormone characteristics generally added significantly to predictions that used sire growth rate alone. The results suggest that serum hormone characteristics in parents may provide additional predictors of growth rates of progeny. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science.