McEvers, T. J., Dorin, L. C., Berg, J. L., Royan, G. F., Hutcheson, J. P., Appleyard, G. D., Brown M. S. and Lawrence, T. E. 2013. Effect of leptin genotype and zilpaterol hydrochloride supplementation on the growth rate and carcass characteristics of finishing steers. Can. J. Anim. Sci. 93: 199-204. Steers (n=960; initial body weight=480.2±35.3 kg) were initially selected by leptin genotype (LG; CC=homozygous normal, CT=heterozygous, and TT=homozygous mutant) from a pool of 1500 candidates, and allocated into 48 pens of which one-half were fed zilpaterol hydrochloride (ZH) for 20 d with a 4-d withdrawal and the balance a control ration. No LG×ZH interaction (P≥0.21) occurred for any measured live production or carcass trait. Cattle of the TT genotype tended (P=0.08) to have lower average daily gain (ADG) and gain to feed ratio (G:F) during the pre ZH treatment period. Cattle fed ZH had greater (P<0.01) ADG and G:F than cattle not fed ZH. Cattle of the TT genotype had greater (P<0.01) lipid depots concomitant with reduced (P≤0.02) lean tissue as compared to cattle of the CC genotype; furthermore, TT cattle tended (P=0.07) to have lighter carcass weights than other genotypes. Cattle fed ZH had increased (P<0.01) hot carcass weight and lean tissue concomitant with decreased (P≤0.01) lipid depots. Commercially available leptin genotyping may allow for antemortem sorting of cattle by genotype, which could augment management strategies ultimately leading to adjustments in feeding duration and timeliness of carcass marketing.
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