Abstract
A program of testing young breeding beef cattle for gaining ability has been conducted since 1942 at the Balmorhea substation. The cattle start on test at 6 to 12 months of age and are self-fed a ground, mixed ration of about 65 percent roughage for a total period of about 140 days. Only data from Herefords were analyzed in this study, which included 1,053 bulls in 166 sire groups and 271 heifers in 46 sire groups. Wide differences in gaining ability were found, ranging from 1.15 to 2.82 lb. per head daily for the average of the sire groups and from 1.37 to 4.08 for individuals. Intra-sire correlation coefficients between half-sibs were 0.3250 and 0.2496 for bulls and heifers, respectively. Several possible causes for these obviously overestimated values are discussed although the data do not allow much precision in estimation. It appears that subsequent gain is little affected or associated with initial grade, initial weight or initial age within the limits of this study and performance records are apparently not greatly biased by these factors. The respec- tive correlation coefficients between subsequent gain and the above three variables are 0.12, 0.11 and 0.12. The correlation coefficient between initial condition and subsequent gain is higher (0.24) and may bias results in extreme cases. On the assumptions of half-sib relationships of 0.25 and zero sire × year interaction, the data gave unrealistically high heritability estimates. When the actual half-sib relationship of 0.33 was used and the sire × year variance removed from apparent sire differences, a heritability estimate of about 53 percent for rate of gain in the feed-lot was obtained. Further discussion is included concerning the relationship of rate of gain to other economic characters and the impact on the beef-producing industry. Copyright © . .