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The Relationship of Insulin-Like Growth Factor-I with Postweaning Performance in Angus Beef Cattle^1,2,3,

The Ohio State University, Columbus 43210

Abstract

This study was designed to evaluate the ontogeny of serum IGF-I (SI) concentrations and its relationship to animal performance in a 140-d postweaning feeding trial. Ninety-eight progeny representing six sires (three high and three low feed conversion) and two sexes (43 bulls and 55 heifers) with ad libitum access to feed were allocated by sire and sex to monitor individual weights and pen feed consumption. Blood serum samples were obtained at the beginning of test (average age of 230 d) and every 28 d thereafter until each animal reached a fat thickness (estimated by sonoray) of 8.9 mm. Individual serum samples were acid-ethanol extracted and measured for IGF-I peptide by heterologous RIA. Serum IGF-I concentrations differed (P < .10) between high (H) and low (L) feed conversion progeny groups at the end of the first 28-d period (125.12 vs 89.52 ng/ml) and tended to differ at the conclusion of the second 28-d period (P < .15). Weight gains of H and L groups tended to differ in the second and third 28-d periods (P = .11 and .10, respectively). Serum IGF-I concentrations differed (P < .05) between bulls and heifers for the first through fourth 28-d periods (P < .01, P < .05, P < .10 and P < .01, respectively). Phenotypic correlations indicated that pens with higher mean SI concentrations at the beginning of the test consumed less feed and had lower cumulative feed:gain ratios. This study demonstrates that selection for an improved economic trait, such as feed conversion, can alter the expression of a single gene product.

¹ Salaries and research support provided by Slate and Federal Funds appropriated to the Ohio Agric. Res. and Dev. Center, The Ohio State Univ. Journal Article no. 28-29.

² The experiment was a contributing project to North Central Regional Project NC-1, "The Improvement of Beef Cattle through Breeding Methods."

³ The authors wish to thank P. Houdashelt, the farm crew at the Northwest Branch, Custar, OH and Cindy Coy, lab technician, Wooster, OH for their excellent technical assistance.

⁴ Dept. of Anim. Sci. and Labs. of Mol. and Dev. Biol., Ohio Agric. Res. and Dev. Center, The Ohio State Univ., Columbus.

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