|Caldwell, L -|
|Riley, D -|
|Spicer, L -|
|Welsh, T -|
|Randel, R -|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2011
Publication Date: December 1, 2011
Citation: Caldwell, L.C., Chase, C.C., Jr., Riley, D.G., Coleman, S.W., Phillips, W.A., Spicer, L.J., Welsh, T.H., Randel, R.D. 2011. The influence of tropical adaptation on plasma concentrations of insulin-like growth factor-I in purebred and crossbred beef cattle. Journal of Animal Science. 89:4017-4022. Interpretive Summary: Researchers have reported favorable correlations between systemic concentrations of insulin-like growth factor-I (IGF-I) and growth in live and carcass weights, average daily gain, feed efficiency, and reproduction. Our ARS laboratory reported that Brahman cows had higher concentrations of IGF-I than Angus cows, and that Senepol cows, a tropically adapted Bos taurus breed, also had higher concentrations than Angus cows. The objective of this study was to determine whether tropical adaptation influences circulating concentrations of the growth-related hormone, IGF-I, in heifers and steers following weaning. Temperate Bos taurus (A; Angus), tropical Bos indicus (B; Brahman), and tropical Bos taurus (R; Romosinuano) heifers and steers were used beginning at weaning and at two additional sampling times. Heifers and steers included 10 of each purebred (AA, BB, RR) and crossbred (AB, BA, AR, RA, BR, RB). Separate analyses were conducted for heifers and steers. The direct effect of Angus was to lower concentrations of IGF-I in heifers, whereas, the direct effect of Romosinuano was to elevate concentrations of IGF-I. In comparison to the temperate Bos taurus breed, tropical Bos taurus and tropical Bos indicus heifers and steers had greater plasma concentrations of IGF-I.
Technical Abstract: In an effort to determine whether tropical adaptation influences circulating concentrations of the growth-related hormone, insulin-like growth factor-I (IGF-I), 3-breed diallel matings were conducted using temperate Bos taurus (A; Angus), tropical Bos indicus (B; Brahman), and tropical Bos taurus (R; Romosinuano). Purebred (AA, BB, RR) and crossbred (ABX, ARX, BRX) heifers and steers were evaluated in 2 separate calf crops from the years 2003 and 2004. Blood samples were obtained from 10 heifers of each breed group (n = 90) for each year at weaning and on d 0 and 84 of postweaning trials. Samples were also taken from 10 steers of each breed group (n = 90) at weaning and on d 0 and 60 of individual finishing phase feeding trials for each year. Concentrations of IGF-I were determined by radioimmunoassay. Analyses included effects of sire breed, dam breed, year of record, the age of calf’s dam in years and interactions. Age of calf in days was investigated as a linear and quadratic covariate. Separate analyses were conducted for heifers and steers. The direct effect of Angus was to lower (P< 0.03) heifer concentrations of IGF-I at d 84 and in the repeated measures analysis. In the repeated measures analysis, the direct effect of Romosinuano was to elevate concentrations of IGF-I (P = 0.01). Relative to the temperate Bos taurus breed, plasma concentrations of IGF-I were greater in male and female tropically-adapted breed groups.