Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 1999
Publication Date: N/A
Interpretive Summary: Current markets in the United States have established that optimum parameters for carcasses are 250 to 400 kg with a yield grade of 3 or less. Systems that produced carcasses within those parameters included HG-A6-T180, MG-A12-T136, MG-A18-T45, HG-A18-T45, HG-A18-T90 and HG-A18- T135. Carcasses also must be produced efficiently with efficiency calculated on the basis of end product rather than just live weight. Within these acceptable systems, efficiency of live weight production was greater for HG-A12-T136 and HG-A6-T180, while that for carcass protein was greatest for HG-A18-T135, which ranked lowest in live weight gain efficiency. The HG-A6-T180 system ranked high in both efficiency of live weight and carcass protein gain per unit of energy intake. Production systems must take into account genetic and management variables as well as economic and biological efficiency to determine optimum systems for beef production.
Technical Abstract: 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 efficiency of production during finishing. Crossbred cows were bred by AI to Charolais or Line 1 Hereford bulls that represented high growth (HG) or moderate growth (MG) rate potential. 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 18 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 for A18. 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, had 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 efficiency, 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 older (A18), HG-sired steers were too large with insufficient fat by current industry standards and younger (A6), MG-sired steers were too small. Our conclusions are that both HG- and MG-sired steers can produce acceptable carcasses for current market standards with comparable efficiencies of live-weight gain, but the growing and finishing strategy must be adapted to the genotype.