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 compo sition of gain of crossbred steers sired by Angus, Hereford, Belgian B lue, or Piedmontese sires from Angus, Hereford, or MARC III dams and 2 ) determine the influence of sire and dam type on energy utilization d uring the finishing period. Beginning at 330 kg, 70 steers were adjust ed to a high-corn diet and individual feeding. Steers were assigned, b y sire and dam breed, to be billed as an initial slaughter group or fe d either a limited amount or ad libitum for 140 d, then killed. Organ weights, carcass traits, and body composition were obtained. Effects i ncluded 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 tr aits were influenced (P <.05) by T. Sire influenced longissimus area, fat thickness, and quality and yield grade (P <.01); weight of hide, s tomach 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) D M and ME intake, fat thickness, yield grade, heart, lung, and spleen w eights, and rates of water, fat, protein, and energy gains. Rates of D M 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 in fluenced (P >.10) regressions of heat production on ME intake. Easting heat production and maintenance were estimated to be 80.6 and 124.4 k cal ME/(kg.(75).d). The nonlinear relationship between energy gain (Y, kcal/[kg(.75.)d]) and ME intake (X, kcal/[kg(.75.)d]) was Y = 74.69 x (1 - 2.60 x exp(-.0159x(ME - 80.597))), and indicated energy gain app roached an asymptote (74.69) as ME intake increased. This relationship also implies that efficiency of ME use for gain decreased as ME intak e increased.