Genetic-enviroment interactions in tropical beef cattle

Abstract

Two trials were conducted with progeny of Brahman bulls, Sta Gertrudis and Romo Sinnano, to determine genetic-environment interactions that could interfere with selection based on progeny tests for post-weaning weight gains. In the first trial, the same calves were first subjected to a diamond paddock environment 100 days post-weaning and immediately thereafter to a stud environment. Changes were observed in the order of merit of the bulls' progenies. One bull, Sta Gertrudis, ranked last in the paddock and first in the stud. This change is attributable to a negative correlation between weaning weight and post-weaning performance in the Sta Gertrudis bull

In the second trial with four bulls, whose progenies were randomly divided into two groups (one for each environment), no significant bull x environment interaction could be detected. One significant sire x environment x year interaction was found. This was of sufficient magnitude to change the order of merit of one Sta Gertrudis bull (among four) from first in one viable year to last among the same four animals the following year. The progenies of two of these others, tested for a third year, revealed data in which one group of sires outperformed the other under paddock conditions, but the reverse occurred in paddocks.

These doubts about the accuracy of selection are of special interest to the small breeder who even carries out his own progeny trials with a few bulls per year to select one or two for breeding. It is concluded that much more data on heritability under paddock conditions and at different ages are needed before sound practical recommendations can be made.