BODY COMPOSITION AND ENERGY-UTILIZATION BY STEERS OF DIVERSE GENOTYPES FED A HIGH-CONCENTRATE DIET DURING THE FINISHING PERIOD - II - ANGUS, BORAN, BRAHMAN, HEREFORD, AND TULI SIRES

Objectives of the study were to determine the influence of Angus (A), Boran (BO), Brahman (BR), Hereford (H), or Tuli (T) sires on body comp osition, composition of gain, and energy utilization of crossbred stee rs during the finishing period. Beginning at 300 kg, 96 steers were ad justed to a high-corn diet and individual feeding. Steers were assigne d, by sire breed, to be killed as an initial slaughter group or fed ei ther a limited amount or ad libitum for 140 d then killed. Organ weigh ts, carcass traits, and body composition were evaluated. The statistic al model included sire breed (S), treatment (Trt), and the S x Trt int eraction. Ad libitum feed intake was least for BO- and T-intermediate for BR- and H-, and greatest for A-sired steers. Rates of weight, fat, and energy gains were similar for A-, H-, and BR-sired steers but les s (P <.01) for BO and T when fed ad libitum. Rates of protein or water gains did not differ among sire breeds (P >.12). Rates of water, fat, and protein gain increased linearly with increased rate of BW gain, b ut relationships differed (P <.05) among sire breeds. Linear regressio n analyses indicated energy requirements for maintenance and efficienc y of energy use for energy gain differed (P <.05) among sire breeds. E valuation by nonlinear regression indicated that heat production incre ased exponentially and energy gain increased asymptotically as feed in take increased above maintenance.