Some factors affecting weaning weights of calves.

Abstract

A mixed model study was carried out on the field data records of 9798 Simmmental and 1725 Hereford calves born during the period 1992 to 1994, and obtained from the Animal Improvement Institute, Irene. The records were used to evaluate the influence of type of management systems used by breeders, type of vegetation, sex of calf, age of dam, year of birth and season of birth on 205 day weight of calves and some two way interactions between these effects. The analysis were carried separately for each breed. Type of management did not significantly affect the 205 day weight of Hereford calves, the least-squares means of calves from extensive, semi-extensive and intensive systems were 195.8, 196.9 and 197 kg, respectively. However, the effect was highly significant (P<.01) for Simmmental calves with weaning weights of 217.4, 238.3 and 261.2 kg for extensive, semi-extensive and intensive production systems, respectively. The Simmmental data were divided for further analysis according to the three management systems. All the main effects on the 205 day weight of Simmmental calves were highly significant for all the management systems. Simmmental calves raised in the combination of fynbos and pastures under the semi-extensive management system weaned the heaviest calves (295.8 kg) and those raised in the mixed grassveld under the extensive system weaned the least (202.4 kg) . The Simmmental male calves were 10, 9.8 and 17.9 kg heavier than female calves in the extensive, semi-extensive and intensive systems respectively. The mature age of the dam was between the 52 to 57, 58 to 117 and 52 to 57 month age groups with weaning weights of 230.7, 257.7 and 266.4 kg in the extensive, semi-extensive and intensive systems respectively. The deviations of weight of calves of the mature dams from those of young dams (16 to 27 months) were 26.9, 30 and 20 kg under the extensive, semi-extensive and intensive systems, respectively. The main effects on the 205 day weight of Hereford calves, except the type of management, were highly significant (P<.01). The Hereford calves raised in the sweetveld areas produced the highest weights (218.6 kg) but those raised on the karroo were the lightest (188.1 kg). The best calving seasons were autumn and winter, with the mean weight of 215.1 kg and 202.9 kg, respectively. Summer and spring born calves weighed 180.2 and 188.2 kg, respectively. The Hereford male calves were 13.2 kg heavier than the heifers. The maturity age of the dams was between the 72 to 95 month age group with the deviation of 20 kg in weaning weight of their calves from those of the young dams (22 to 27 months old). The sex and age-of-dam interaction for both breeds indicated an overall correction factor for sex of calf and of age of dam. Multiple adjustment factors were used to remove sex of calf differences, whereas additive adjustment factors were used to remove age-of-dam differences.