Pre-weaning supplements for cows and calves on low quality pastures for improved reproductive rates

Abstract

Animal Production in Australia 1998 Vol. 22 PRE-WEANING SUPPLEMENTS FOR COWS AND CALVES ON LOW QUALITY PASTURES FOR IMPROVED REPRODUCTIVE RATES J.F. WILKINS and D.W. HENNESSY NSW Agriculture, PMB 2 Grafton, NSW 2460, and the CRC for the Cattle and Beef Industries Production from cattle breeding enterprises in northern coastal New South Wales is limited by low quality pastures, often resulting in poor reproductive rates and low calf weaning weights, which may be improved by protein supplements (Hennessy and Williamson 1988). Poor nutrition can affect reproduction by delaying the resumption of regular ovarian function after calving (Jolly et al. 1996), thereby increasing the intervals to oestrus, ovulation and conception, or causing complete failure. Cows were supplemented twice a week from calving with 4.2 kg/head (per feed) of cottonseed meal (37% crude protein), and their ovarian activity and fertility were compared with unsupplemented cows. Calves of half the cows within each treatment group had access to a pelleted diet (30% crude protein, 12 MJ/kg ME) in a creep from approximately 75 days of age. There were four to eight replicates, (five or six cows per rep.) of each of the four treatment groups (total 123 cows). Cows were synchronised for AI with a seven day progesterone and prostaglandin regime, and inseminated following oestrus detection. Ovarian activity was determined by ultrasound examination (Aloka 210 DXII, 7.5 Mhz), at 12 to 14 days after AI, and again at approximately five weeks after weaning. There were significant beneficial effects of supplementation of the cow on ovarian activity, proportions presented for AI, and pregnancy rates (Table 1). Proportions of cows ovulating were considerably higher than those detected in heat by visual observation (in all treatments), a problem attributed to low mounting activity in small groups, and probably related to social facilitation. None of the differences due to calf supplementation (as a main effect) approached significance (Table 1), nor were there any significant interactions between cow and calf treatments. However, when the effects of both cow and calf supplements were analysed as an additive treatment effect with four levels (cow nil/calf nil; cow nil/calf supp; cow supp/calf nil; cow supp/calf supp), there were significant linear responses in proportions of cows with CL (41, 55, 87 and 90%; P<0.001) and proportions presented for AI (27, 40, 51 and 65%; P<0.005). The effect on pregnancy rate for two cycles was also significant (14, 30, 41 and 35%; P<0.05) and linear, even though affected by the non-linear pattern (non-significant) in conception rate of inseminated cows (42, 63, 65 and 31%). The supplemented cows which failed to conceive had greater ovarian activity following weaning. These results highlight the importance of providing strategic supplements directly to cows in herds grazing low quality pasture. Supplementing the calf may lower the demand on the cow, and also lower the suckling frequency. Either or both of these effects could decrease inhibitory effects on ovarian activity through pituitary feedback. Table 1. Ef fects of cow and calf supplement treatments on ovarian activity at the time of ar tificial insemination, conception rates and post weaning ovarian activity Cow supplement Proportions of cows (least sq. means, %) With active ovaries C With cystic follicles or CL With active CL D Ovulated without detection Detected and given A I Conceived (of those AId) Pregnant to 1st cycle AI (of totals in groups) Pregnant to two cycles of A I E With CL post weaning B B Calf supplement 82 10 64 28 39 56 22 27 58 A 70 11 47 20 34 49 16 20 48 + 99*** 6 90*** 33 58** 50 A 29 40* 76** + 88 8 73 25 53 43 23 33 67 Significant differences within main effects:- ***P<0.005; **P<0.01; *P<0.05; P~ 0.08; C D Cows having active CL or follicles 10mm; follicles 20mm or luteinised; not detected in estrus (and not E presented for AI) but had active CL; of cows not already pregnant to A I HENNESSY, D. W. and WILLIAMSON, P. J. (1988). Aust. J. Exp. Agric. 28, 439-46. JOLLY, P. D., McSWEENEY, C. S., SCHLINK, A. C., HOUSTON, E. M. and ENTHWISTLE, K. W. (1996). Aust. J. Agric. Res. 47, 927-42. 403