Evaluation of sire x environment interaction effects to improve some growth traits of American Brahman cattle (Bos indicus L.)

Growth traits (i.e., birthweight, weaning weight, and average daily gain at pre-weaning) measured on 403 purebred American Brahman calves born from Jan 2000 to Jan 2007 at ANSA Genetics, Inc., Lipa City, Batangas [Philippines] were analyzed by general least squares procedures for unbalanced data using a linear model containing independent variables (i.e., sire, sex of calf, weaning month and weaning year), two-factor interactions (i.e., sire x calfing year, sire x weaning month) and covariates (i.e., gestation length, birth weight, age at weaning and dam weight at calving and at weaning). Birth weight was significantly affected by the sire, sex of calf and interaction between sire and calving year (P less than 0.01). Birth weight was also positively correlated with longer gestation length (r=0.28) and heavier dam weight at calving (r=0.21). Weaning weight was significantly affected by the sire (P=0.06), weaning month and year (P less than 0.01) and the interaction between sire and weaning month (P less than 0.05). Weaning weight was also positively associated with heavier with birth weight (r=0.24) and older age at weaning (r=0.22). Average daily gain at pre-weaning was significantly affected by the sire (P less than 0.05), weaning month and year (P less than 0.01) and the interaction between sire and weaning year (P less than 0.01). Average daily gain in weight at pre-weaning was also positively associated with heavier dam weight at weaning (r=0.28). Without genotype x environment interaction, the significant differences in pre-weaning growth traits may be utilized to identify sires that are to be used extensively in artificial insemination programs and to promote a premium price for frozen semen produced from superior sires. In contrast, sire x environment interactions imply that sires rank differently in terms of pre-weaning growth traits at different calving years and months of weaning.