Performance of young breeding cattle in commercial herds in the south-west of Western Australia. 3. Calf growth, dystocia, and their relationship with production and fertility measurements in first-calf heifers

The preweaning growth of the progeny from 2531 first-calf heifers calving on commercial properties in the south-west of Western Australia was studied over 5 years. Animals included the progeny of Angus sires mated to Angus, Angus x Friesian, Simford, Hereford and Beef Shorthorn crossbred heifers; the progeny of Hereford sires mated to Hereford, Hereford x Friesian, and Beef Shorthorn crossbred; and those of Devon crossbred, Simford or Wokalup multibreed heifers mated inter se. Calves were born between mid January and July of each year and date of birth, calving information and calf growth through to weaning at an average age of 230 days were recorded. Data recorded on the calves' dams included regular liveweight and condition score assessment and the date of second calving. Angus-sired calves were lighter at birth than Hereford-sired calves; breed means ranged from 25.1 kg for purebred Angus to 33.2 kg for Wokalup multibreeds, with male calves weighing 1.4 kg more than females at birth. Calf birth weight was positively and linearly related to weight of dam at the beginning of joining. Breed of calf, sex of calf, year of birth, day of the year born, liveweight and liveweight change of the dam at the beginning of rejoining all significantly influenced calf growth, with up to 64% of variation accounted for. At 50 days of age, Devon crossbreds, Simfords and Wokalup multibreeds were significantly heavier than crossbred Hereford or Angus calves, and this trend persisted until weaning. The average growth rate to 200 days of Angus calves was 0.113 kg/day slower, and Hereford calves 0.77 kg/day slower, than the average growth rate of their respective crossbred calves. Heaviest 200-day weights were found in Devon crossbred (235 kg), Simford (221 kg) and Wokalup multibreed (219 kg) calves. A strong seasonal influence on calf growth was detected. Each 1 day increase in calf age in calves born between mid January and June resulted in 0.29 kg extra liveweight at 100 days and 0.68 kg extra liveweight at 200 days of age. Overall, the liveweight of the dam at the beginning of re-joining was positively associated with calf growth, with 0.119 kg of calf liveweight/kg dam liveweight at 100 days and 0.123 kg at 200 days. There was less effect of dam liveweight in Herefords and Hereford x Friesians on calf growth to 200 days, but this relationship was closer in faster growing and later maturing breeds, including Angus x Friesian, Simford, and Wokalup multibreed. The dairy crossbreeds generally lost weight at the beginning of re-joining, resulting in a negative association between this weight change and calf growth to 100 days. No assistance was required in 93% of calvings and the highest incidence of dystocia corresponded with the highest birth weight calves in Wokalup multibreeds. The most common calving difficulty was an apparently slow birth where no assistance was given, resulting in a stillborn calf. Male calves experienced 3 times the level of dystocia recorded for female calves. There was no association detected between dystocia and dam liveweight subsequent to calving. The study highlighted the importance of dam breed, liveweight and condition of the dam and timing of calving as important influences on the growth of progeny reared by first-calf heifers.