Effects of sire growth potential, growing-finishing strategy, and time on feed on performance, composition, and efficiency of steers

Beef production systems that increase use of unharvested forages and use an imals with greater potential for gain affect age and size of animals placed on a finishing regimen. This experiment was conducted to evaluate effects of genetic potential for gain, age at the start of a finishing period, and time on feed on composition, quantity, and quality of beef produced and eff iciency of production during finishing. Crossbred cows were bred by AI to C harolais or Line 1 Hereford bulls that represented potentially high (HG) or moderate growth (MG) rates, respectively, to produce spring- or fall-born calves. Steer calves from these matings were placed on an individually fed finishing diet at three ages (A). Spring-born steers were started at 6 or 1 8 mo of age (A6 and A18), and fall-born steers were started at 12 mo of age (A12). Slaughter times (T) were at 0, 90, 180, and 270 d for A6; 68, 136, and 204 d for A12; and 0, 45, 90, and 135 d for A18. Data collected on each animal included feed intake, growth, chemical composition of the complete body and carcass, and quantitative and qualitative assessment of the meat p roduced. Four steers of each sire group were slaughtered in each of the 11 A-T treatment groups, and the experiment was repeated for 2 yr in the A12 g roups and 3 yr in the A6 and A18 groups (n = 237). Steers sired by HG bulls were larger and produced larger carcasses and more carcass protein than MG -sired steers (S, P < .05 or .01). Steers sired by MG bulls were fatter, ha d higher quality grades, and accumulated fat at a faster rate than HG-sired steers, and this effect was greater in older steers (G and GA, P < .05 or .01). Sire growth potential did not affect gain, intake, live weight effici ency, tenderness, or taste panel scores (P > .2). Steers sired by HG bulls were more efficient at producing carcass weight and carcass protein at A12 and A18 than were MG-sired steers. At the end of the finishing period, olde r (A18), HG-sired steers were too large with insufficient fat by cm:rent in dustry standards, and younger (A6), MG-sired steers were too small. Our con clusions are that both HG- and MG-sired steers call produce acceptable carc asses for current market standards with comparable efficiencies of live-wei ght gain, but the growing and finishing strategy must be adapted to the gen otype.