Body composition and energy utilization by steers of diverse genotypes fed a high-concentrate diet during the finishing period: I. Angus, Belgian Blue, Hereford, and Piedmontese sires.

Objectives of the study were to 1) describe body composition and composition of gain of crossbred steers sired by Angus, Hereford, Belgian Blue, or Piedmontese sires from Angus, Hereford, or MARC III dams and 2) determine the influence of sire and dam type on energy utilization during the finishing period. Beginning at 330 kg, 70 steers were adjusted to a high-corn diet and individual feeding. Steers were assigned, by sire and dam breed, to be killed as an initial slaughter group or fed either a limited amount or ad libitum for 140 d, then killed. Organ weights, carcass traits, and body composition were obtained. Effects included in the statistical model were nutritional treatment (T), sire breed (S), dam breed (D), and the S x T and D x T interactions. All traits were influenced (P < .05) by T. Sire influenced longissimus area, fat thickness, and quality and yield grade (P < .01); weight of hide, stomach complex, heart, lung, spleen, empty body fat, protein, ash, and energy; rates of fat, protein, and energy gains; and water, fat, ash, and energy content of gains (P < .10). Dam breed influenced (P < .10) DM and ME intake, fat thickness, yield grade, heart, lung, and spleen weights, and rates of water, fat, protein, and energy gains. Rates of DM or ME intake, live and empty body weights, and water, protein, ash, and energy gains were influenced (P < .05) by D x T. Neither S nor D influenced (P > .10) regressions of heat production on ME intake. Fasting heat production and maintenance were estimated to be 80.6 and 124.4 kcal ME/(kgx75xd). The nonlinear relationship between energy gain (Y, kcal/[kgx75xd]) and ME intake (X, kcal/[kgx75xd]) was Y = 74.69 x (1 - 2.60 x exp(-.0159x(ME - 80.597))), and indicated energy gain approached an asymptote (74.69) as ME intake increased. This relationship also implies that efficiency of ME use for gain decreased as ME intake increased.