Sex and some environmental factors effects on birth weight of Nelore Calves

Abstract

Birth weight of 1,372 Nelore calves born from 1975 to 1980 from cows between the 1^st and 10^th parity was analysed using the Stepwise Method of multiple regression analysis. Four variables were selected (P<0.01): Sex of calf, year and month of birth, and calving parity of dam. The average birth weight was 29.01 ± 2.58 kg. Male calves were 0.90 kg heavier than females. Year of birth determined a guadratic curve with minimum in 1976. Age of dam influenced birthweight in a guadratic way, with a maximum in the 5^th and 6^th parity. Month of birth determined a cubic curve, with a maximum weight for animals born on March/Abril and a minimum for those born on July/August. Nutrition and reproductive management seemed to explain these results.