The objective of the present study was to evaluate the effect of calving season, genotype and calf sex on the cows weaning individual efficiency ( percentual relationship between cow body weight and calf weaning weight), birth and weaning weight of calves. Forty-eight primiparous Hereford cows with approximate average age of 3 years and grazing only native pastures were used. Sixteen inseminated with one Red Angus bull (Bos taurus) and 32 with Nelore (Bos indicus). Effects studied were calf genotype (GENOT), Bos taurus x Bos taurus and Bos taurus x Bos indicus, calving season (EPOCN) concentrated in the Spring and subdivided into three periods: 1S (September), 2O (October) and 3N (November and December) and calf sex (SEXO). Milk production (PL) was included as co-variable. Ten measurements of milk production obtained by the indirect method, weighing the calf before and after suckling, and eleven measurements of cow and calf weights, were made at 21 day intervals. Effects with significant influence on PN were GENOT and SEXO (P<0.05). P205 was significantly affected by EPOCN, SEXO and PL (P<0.05). EI was significantly affected by EPOCN, SEXO and PL until 147 days (P<0.05). Calf genotype and sex affected their birth weight. Weaning weight and cow efficiency are affected by sex and and calving season, but not by calf genotype.
beef cattle; cow efficiency; birth weight; weaning weight
