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 composition, composition of gain, and energy utilization of crossbred steers during the finishing period. Beginning at 300 kg, 96 steers were adjusted to a high-corn diet and individual feeding. Steers were assigned, by sire 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 evaluated. The statistical model included sire breed (S), treatment (Trt), and the S × Trt interaction. 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 less ( P .12). Rates of water, fat, and protein gain increased linearly with increased rate of BW gain, but relationships differed ( P < .05) among sire breeds. Linear regression analyses indicated energy requirements for main- tenance and efficiency of energy use for energy gain differed ( P < .05) among sire breeds. Evaluation by nonlinear regression indicated that heat production increased exponentially and energy gain increased asymptotically as feed intake increased above main- tenance.