Efficiency of Feed Use in Beef Cattle

Feed efficiency measured as a function of gain in body weight and feed consumed was studied for 1,324 bull and heifer calves at three experiment stations. Three measures were computed: (1) feed consumption adjusted for differences in gain; (2) gain adjusted for differences in feed consumption; and (3) the ratio of gain to feed consumed. In all three measures, mid-weight was considered simultaneously in an attempt to remove differences in maintenance requirements. Efficiency expressed as gain adjusted for differences in feed consumption (i.e., ±deviation from the regression of gain on consumption) was considered the most accurate mathematical description of the cause and effect relationships and resulted in the highest heritability of the three measures studied. No trends in the heritabilities calculated for each experiment station were noted. The combined heritabilities were 0.65 for gain on test, 0.64 for feed consumed, 0.62 for gain adjusted for differences in feed consumption, 0.28 for feed consumption adjusted for differences in gain, and 0.36 for the ratio of gain to feed consumed. A path analysis of feed efficiency (gain adjusted for feed consumption), feed consumption and gain was made. The analysis indicated that 38% of the variation in gain could be attributed directly to genetic differences in feed efficiency. Genetic differences in feed consumption accounted for 25% of the variation in gain. The remaining 37% of the variation in gain was accounted for by variations in environmental influences. The genetic correlation between feed efficiency and gain was 0.79, between feed consumption and gain was 0.64, and between feed efficiency and feed consumption was 0.04. These results indicate that selecting for gain should be effective and lead to both increased feed efficiency and increased feed consumption. Selecting for feed efficiency would increase feed efficiency and result in increased daily gain, but feed consumption would not be affected. Selection for feed consumption would increase feed consumption and daily gain, but would lead to no improvement in feed efficiency other than that attributable to a smaller portion of the intake being used for body maintenance.