Adjustment of Postweaning Feed:Gain Ratios of Angus Bulls for Differences in Maintenance Requirements3

Effects of adjusting postweaning feed:gain ratios for differences in maintenance requirements as recommended by the Beef Improvement Federation were examined utilizing 171 individually fed, purebred Angus bulls. The residual correlation (year and sire effects removed) between unadjusted and adjusted feed efficiency was .85 (P<.01). The Spearman correlation between ranks of the bulls based on the two measures of efficiency was .79 (P<.01). Although product-moment and rank correlations between unadjusted and adjusted feed:gain ratios were large, the two methods of evaluating efficiency often identified different bulls as being among the four most or four least efficient in the conversion of feed into postweaning gain. When unadjusted feed:gain ratios were used to evaluate efficiency, bulls that were more efficient were lighter in weight at the beginning of the 140-d postweaning performance test, gained more rapidly and consumed less feed during the test, and were taller and leaner at the conclusion of the test. When differences due to maintenance requirements were removed, bulls that gained more rapidly and were heavier, taller and slightly fatter at the end of the test were superior in the conversion of feed into postweaning gain. Correlations of on-test weight and feed consumption with adjusted feed:gain ratios were near zero. On-test age was not closely related to either adjusted or unadjusted feed efficiency.