Temporal Patterns of Growth Hormone, Prolacting and Thyrotropin Secretion in Targhee Rams Selected for Rate and Efficiency of Gain

Abstract

Thirteen Targhee rams selected for rate and efficiency of gain for 4 yr (1.5 generations) were compared with 10 rams from a Targhee line with no selection for over 20 yr to determine if selection for these traits would be associated with changes in the secretion of growth hormone (GH), thyrotropin (TSH) and(or) prolactin (PRL). Selected rams exhibited greater birth weight, average daily gain (ADG) and feed consumed/day during a 6-wk individual feeding regimen, and exhibited greater overall ADG during a 16-wk feeding trial as compared with the unselected rams. Temporal blood plasma samples were collected at 15-min intervals for 8 h from each of the 23 rams for hormone analysis. Selected rams exhibited greater overall mean GH (6.1 +/- .4 vs 4.6 +/- .5 ng/ml), overall mean TSH (8.6 +/- 1.2 vs 6.2 +/- .7 ng/ml) and baseline mean TSH (8.0 +/- 1.1 vs 5.6 +/- .5 ng/ml) than the unselected rams. Although the adjusted GH spike amplitude value was higher in the selected line (12.1 +/- 3.0 vs 7.4 +/- .8 ng/ml), this difference was not significant. No differences were observed with any of the variables of PRL secretion. In addition, there were no significant correlations between any of the hormone variables and any of the feed or gain data. These data support the hypothesis that Targhee rams selected for rate and efficiency of gain exhibit higher plasma levels of GH and TSH than unselected rams of the same breed.

Estimates of genetic parameters and selection strategies to improve the economic efficiency of postweaning growth in lambs1

“…Three studies have investigated the biology of the animals used in this study by comparing selected and random bred control lines. Selection for rate of gain resulted in higher levels of plasma growth hormone and thyrotropin levels (Dodson et al, 1983); greater tissue oxygen consumption rates (Rompala et al, 1987); and a 4% decrease in metabolizable energy for maintenance, 7.8% increase in fasting heat production, and 13% heavier ruminal weight (Rompala et al, 1991). The lower maintenance requirement for metabolizable energy would be of economic importance.…”

Candidate gene markers associated with somatotropic axis and milk selection☆

“…Effects of this action are modulated by several other hormones [13]. Some parameters of GH secretion (for example, frequency of GH peaks, total daily GH secretion, or GH response to GHRH stimulation) were associated with higher genetic values in studies comparing GH secretion of more highly selected and control lines of cattle [14 -16], sheep, [17] or pig [18]. On the contrary, Weber et al [19] recently reported that selection for milk yield in multiparous Holstein cows increased mean GH and GH peak height but did not affect GH peak frequency or IGF-I plasma levels.…”

Periodic 48 h feed withdrawal improves glucose tolerance in growing pigs by enhancing adipogenesis and lipogenesis

“…It is known that GH is a trophic hormone (through Insulin like Growth Factor) and that feed restriction [30] in cattle and fasting in humans [31] increases its concentration to act as a repartitioning agent, and to increase organomegaly [32,33]. Thus in sub-experiment 2 we evaluated the role of this hormone in adipogenesis.…”