Genotype X environment interaction in Hereford cattle: III. Postweaning trait of heifers.

The postweaning performance of heifers from contrasting lines of Hereford cattle was compared simultaneously at Miles City, Montana and at Brooksville, Florida in an experiment designed to evaluate the importance of genotype X environment interactions in beef cattle. During Phase 1 of the study (1964 to 1973), the performance of two unrelated lines, M1 and F6, was compared at the two locations. During Phase 2 (1967 to 1974), two related lines, M1 of Montana origin and F4 derived from M1 by selection in Florida, were compared at each of the two locations. The line X location interaction term was highly significant in either Phase 1, Phase 2 or both for weaning weight, daily gain from weaning to spring, spring yearling weight, daily gain from weaning to fall, fall yearling weight, yearling condition score, conformation score, wither height, body depth, body length, shoulder width, hook width and forecannon circumference. Daily gain of yearlings from spring to fall was the only objective measurement for which the interaction term was nonsignificant in both phases. These results, consistent with the results on performance to weaning age reported previously, indicate the existence of highly significant genotype X environment interactions in beef cattle. The results indicate that genetic adaptation to the local environment is important in beef cattle production and should be considered in designing breeding programs or performance testing procedures and in interregional transfer of breeding stock.