Growth and Muscle Development of Feedlot Cattle of Different Genetic Backgrounds

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Abstract
The effects of crossbreeding, cattle type and dietary energy level on semitendinosus muscle (ST) development, feedlot performance, daily carcass protein and fat gain and serum anabolic hormone concentrations were studied. Over 3 consecutive years, 176 feedlot steers representing four cattle types — unselected Hereford (UH), selected Hereford (SH), Angus ✕ Hereford ✕ Charolais (AHC) and Angus ✕ Hereford ✕ Holstein (AHH) — were fed either an all-corn silage (HS) or a high grain (HG) diet. Steers were slaughtered on day 1 and at the end of the feedlot trial, and ST muscles were removed rapidly. During years 2 and 3, single blood samples were obtained from steers on days 1, 29, 57, 113 and 169, and analyzed for insulin and growth hormone (GH). Steers fed HG had a higher (P<.005) average daily gain (ADG) than steers fed HS, and cattle type had an effect (P<.005) on ADG. Cattle type and HG affected (P<.005) daily carcass protein and fat gain. Weight of ST muscle and total muscle RNA, DNA and protein content increased with frame size, and HS steers had heavier (P<.05) ST muscles than the HG steers. Steers fed HG had higher (P<.01) serum insulin concentrations than steers fed HS, but there were no consistent cattle type effects. Serum GH concentrations were not affected by cattle type or diet. Serum insulin concentrations, combined across diet and cattle types, were correlated (P<.01) with ADG; however, serum GH, assessed on the same basis, was not related to ADG. Average daily protein and fat gain were positivelyrelated to serum insulin and were negatively related to serum GH. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.