A biometrical evaluation of certain genetic and environmental parameters in a large herd of Santa Gertrudis cattle

Abstract

Production data from a large herd of Santa Gertrudis cattle were analyzed to estimate the importance of certain genetic and environmental parameters. Partial records were available for 6,436 weaning calves from 2,927 different cows. These data were recorded during the years 1952 through 1958 from a privately owned herd. The complete least squares method of fitting constants was used to study the significance of the main effects and to estimate the parameter constants. The economic traits evaluated in this study were weaning weight, weaning type score, long yearling weight and calving internal. Environmental effects were found to be a significant source of variation for all traits studied. The year effect was consistently a highly significant influence on each of the four traits. All effects studied had a highly significant influence on weaning weight. Results indicated that calf weaning weights should be adjusted for the effects of age of calf at weaning, age of dam and season of calf birth if accurate selections are to be made. The heritability of weaning weight, based on 811 calves, was estimated from the sire component of the paternal half-sib analysis to be .56 (plus or minus sign) .15. A second estimate was .18 (plus or minus sign) .18 from corrected weaning weight data by the intra-sire regression of offspring on dam (188 pairs). Weaning type score was significantly affected by all environmental effects studied except season of birth. Analysis indicated that weaning type score should be adjusted for the effects of age of calf at weaning and age of dam. The heritability of weaning type score was estimated by the previously mentioned methods to be .34 (plus or minus) .12 and .12 (plus or minus sign) .18 respectively. The Santa Gertrudis Breeders International herd classification was found to have a highly significant influence on both weaning weight and weaning score. This result indicates that those factors influencing the breed classification at long yearling age also exert a significant influence on weaning performance of the offspring..