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

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 EFFECT OF LIVEWEIGHT AT WEANING AND POSTWEANING SUPPLEMENTATION ON RETURN TO OESTRUS IN EARLY WEANED BOS INDICUS CROSS COWS A. C. SCHLINKA, P. D. JOLLYB, C. S. McSWEENEYA, E. M. HOUSTONA, J. P HOGANA and K. W. ENTWISTLEB ACSIRO Division of Tropical Animal Production, Davies Laboratory, PMB PO. Aitkenvale, Townsville, Qld 48 14. BGraduate School Tropical Veterinary Science and Agriculture, James Cook University, Townsville, Qld 48 11. 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. Table 1. Cow LWT after calving (LWT-C), at weaning (LWT-W), and LWT (LWT-P) and percentage cycling 6 weeks after weaning Means with different letters within columns and experiments are significantly different. All cows heavier than 370 kg at weaning cycled within 6 weeks. PW-Sup of cows in experiment 2 increased the percentage cycling within 6 weeks of weaning (P=O.O5, Fisher' exact test), with no s difference between energy or protein inputs. Logistic regression analvsis of combined data showed percentage cycling was influenced by cow LWT at weaning (P<O.Ol) and PW-Sup (P=O.O2), but not by postcalving LWT (P=O.75). The odds of a cow cycling increased 2.8 times for every 20 kg increase in LWT at weaning, and 8.8 times if fed a PW-Sup. Onset of cyclic@ in response to weaning was affected by cow LWT at weaning. Postweaning supplementation increased the likelihood of ovulation in cows of low LWT. This work was partially funded by the AMLRDC. McSWEENEY, C. S., JOLLY, l? D. and ENTWISTLE, K. W. (1990). Aust. Sot. Reprod. Biol. 22: 138. SCHLINK, A. C., GIBSON, D. S., LIANG, 2. J. and DIXON, R. R. (1988). Proc. Aust. Sot. Anim. Prod. 17: 326. 428