Time of joining affects the performance of young Angus and Angus multiply Friesian cattle in the south-west of Western Australia. 2. Calf productivity and its relationship with milk production and reproduction in first-calvers

Abstract

In a 3-year study using 183 Angus and 173 Angus x Friesian first-calf heifers, calf birth weight, growth, and efficiency of production were measured for 3 calving times: April (conventional), March (4 weeks earlier), and May (4 weeks later). Measurements included calving outcome; calf birth weights and weight gains; and liveweight, condition, milk yield, and reproductive performance of first-calving dams. Calves born to Angus or Angus x Friesian dams in March or May, respectively, were 1.2 or 1.5 kg heavier at birth than those born in April and were associated with more protracted, difficult calvings and calf losses. Heavier dams gave birth to heavier calves (partial regression coefficient 0.028; value almost doubled for later born calves). Calves born early grew more slowly (by 0.1 kg/day) than calves born at, or later than, the onset of pasture growth (April). The effect was present until weaning but was especially marked at 50-150 days of age. During this period milk production of the dam and available pasture influenced calf growth. Hence, calves from Angus x Friesian dams grew faster (by 0.12 kg/day) than calves from Angus dams until 150 days of age. Thereafter, the difference in growth rate was halved. There was a positive relationship between both liveweight and condition of the 2 breeds of dam at the start of second joining and the growth rate of their calves up to 100 days of age (faster by 0.02 kg/day for every 10 kg dam liveweight). Angus x Friesian dams produced more milk (by about 2.0 kg/day) than Angus dams, resulting in faster growth (by 0.07-0.1 kg/day) of crossbred calves and an advantage of 27.1 kg over Angus calves at weaning. Calf growth and milk yield of dam were significantly associated at 51-200 days for crossbreds and at 51-100 days for Angus. The better milking ability of the crossbred dams did not fully offset the poorer growth made by calves born early. Few calves were suitable for slaughter as weaners for the domestic market. Later born calves grew fastest, but the reduced second conception rates of their dams in restricted joining periods and the lower age of calves at weaning adversely affected total calf productivity following later calving. Similarly, early-born calves grew more slowly and incurred extra production costs through supplementary feeding of their dams with no advantage demonstrated in the fertility of these first-calvers. Varying the time of calving of first-calf heifers from that of the main herd calving around the break of season is not recommended for beef herds relying mainly on seasonal nutrition from pastures.