This research was carried out to evaluate the inbreeding effects and its possible influence on the beef cattle growth. Data with 27,406 observations of weaning weight, standardized to 205 (WW), and 14,317 observations of yearling weight, standardized to 365 days (YW), from Gyr breed animals, from 1970 to 1995, were used. The analysis were made using the least square method that included the random effect of contemporary group and the fixed effects of generation (class), age of cow at calving, calf and cow inbreeding as regressions, considering linear and quadratic effects. Only 11.65% of cows, 19.84% of bulls and 9.23% of the studied calves from the Gyr breed presented some degree of inbreeding. The estimates of the inbreeding means were of low magnitude and the values were of 1.04, 0.96 and 1.66% for cows, bulls and calves, respectively. The animal inbreeding was significant and quadratic for both studied traits. The results showed inbreeding depression for both traits (WW and YW). Intentional inbreeding matting should be avoided and matting should be planed also taking into account the relationship between the animals, in order to keep inbreeding in low degree.
Gyr cattle; inbreeding; weaning weight; yearling weight
