Effect of liveweight at weaning and post-weaning supplementation on return to oestrus in early weaned Bos indicus cross cows.

Low pregnancy rates associated with prolonged post-partum anoestrus are a major constraint to beef cattle production in northern Australia, and can be increased by early weaning (Schlink et al. 1988). However, response to weaning may be markedly delayed in cows in poor condition (McSweeney et al. 1990). The relationship between liveweight (LWT.) at weaning and the extent to which postweaning supplementation (PW-Sup) affected the resumption of cyclicity in first-calf Droughtmaster cows was examined in 2 experiments. Experiment I. Diets before and after weaning at 7 weeks were H-H, H-L, L-H and L-L, where H = ad libitum roughage (40% DMD; 8.5 g N/kg DM) plus 1.5 kg maize:formaldehyde-treated sunflower meal (FSSM) 2:l; and L = 60% (per kg LWT) of the ad Zibitum roughage intake of H-cows. Experiment 2. Cows were fed the L diet from calving until weaning at 10 weeks, and then the L diet with either no supplement (C), or mixtures of maize, urea, casein and FSSM that provided 3.5 MJ ME and 420g CP (P), 26.1 MJ and 147 g CP (E) or 26.1 MJ and 420 g CP (P + E). All cows were fed individually in covered pens. Plasma progesterone (P4) levels were determined weekly until weaning, and then twice weekly for the next 6 weeks. Onset of cyclicity was determined from P4 profiles showing cyclic rises >l ng/mL.