Kononoff, P. J., Defoor, P. J., Engler, M. J., Swingle, R. S., James, S. Y., Deobald, H. M., Deobald, R. L., Woronuk, G. N. and Marquess, F. L. S. 2015. Performance and carcass characteristics when sorting feedlot cattle on the basis of phenotype, and leptin genotype along with differential use of β-adrenergic agonists. Can. J. Anim. Sci. 95: 455-463. Crossbred steers were used in a randomized complete block design to evaluate a feedlot cattle sorting system. The sorting system combined information on live body weight, ultrasound fat thickness, coat color, and genotype on the leptin R25C genotype. Using described sorting criteria, a total of four groups (Groups 1-4) of cattle were created along with a randomly selected unsorted control (Group 5), with Groups 1 through 5 representing experimental treatments, and placed in one of five pens within each block. Block was replicated 10 times thus n equaled 50. All cattle were administered zilpaterol hydrochloride except Group 3, which we hypothesized would have a greater proportion of cattle reaching a higher value Quality Grade, and as a result administered ractopamine hydrochloride. The initial body weight of cattle was similar (P=0.426) between the control Group and Groups 1-4. Initial fat, as measured by ultrasound, was also observed to be similar (P=0.256) between these two groups. Overall, when cattle included in Groups 1-4 were compared with Group 5, hot carcass weight was greater (P=0.040), while the proportion of excessively heavy weight carcasses was less (P=0.049). Additionally, hot carcass weight gain tended (P=0.096) to be higher for Groups 1-4 compared with Group 5. No differences (P≥0.129) were observed for calculated yield grade. On average, cattle included in the Sorting Groups 1-4 returned $23 more per head than those in Group 5.
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