Effect of calving time, maternal age and sex on the performance pre-weaning of Nelore (Bos taurus indicus) calves extensively raised in Middle West of Brazil

Abstract

Birth weight (PN), weaning weight (PD) and daily weight gain (GMD) of 2.973 Nelore calves born from 1992 until 2003 in an extensive cattle production system in Southwest of Goiás – Brazil, characterized by tropical climate and rainy and dry well defined
seasons, aiming to verify the influence of environment, represented by time of birth, cow age and sex on the pre weaning performance in commercial production systems without defined breeding season. Variance analysis was used, through the GLM procedure applying the Random option and using maternal effect as an aleatory parameter. The mathematical model contained
birth year, calving season, calf sex, calf age nested in sex, cow age (in classes), besides the lineal and quadratic effect of calving age as co-variable. BW, WW and DWG averages were, respectively, 29, 49±3, 45; 183, 62±21, 62; and 0,568±0,088 kg. In conclusion, for the studied region environment effects, as time of
parturition, maternal age and sex influence directly the pre weaning performance of Nelore calves.