The influence of protected cottonseed meal supplementation of a concentrate / pasture diet on the secretion of progesterone in bovine milk.

Abstract

20A 20A The influence of protected cottonseed meal supplementation of a concentrate/pasture diet on the secretion of progesterone in bovine milk J.J. Della_Vedova1, G.C. Simos1, K.H. Myung2, E. Fleck3, P.C. Wynn1 and J.M. Gooden1 1 2 3 Department of Animal Science, University of Sydney, Camden NSW 2570 Department of Animal Science, Chonnam National University, Kwangju, 500_757, Korea Division of Animal Production, CSIRO, Locked Bag 1, PO, Blacktown NSW 2148 Postpartum anoestrus along with poor embryo survival are the two major contributory factors to the low conception rates found in Australian dairy herds. While the anovulatory period postcalving has been attributed to the negative energy balance associated with peak lactation, the cause of the failure to conceive once cyclicity has resumed has not been identified. However, a positive relationship between the circulating concentration of progesterone (P4) during the luteal phase and subsequent conception rates to artificial insemination has been found. Thus any means of maximising P4 secretion may assist in improving conception rates. The addition of linoleic acid to luteal cells in culture has been shown to enhance P4 secretion. We have investigated the influence of formaldehydetreated cottonseed meal, a dietary lipid source rich in linoleic acid (C18:2) protected from ruminal biohydrogenation, on milk P4 levels in oestrus synchronized cows. Multiparous Friesian cows lactating for 60140 d were assigned to one of three groups (n=10) by stage of lactation and offered 10 kg DM of a concentrate ration balanced for energy and nitrogen content and containing either 0,1 or 2 kg of PCM in addition to ryegrass/kikuyu ad libitum. Oestrus was synchronized using CIDRR on days 6 and 26 following the commencement of dietary supplementation. Daily (a.m.) milk samples were analysed for P4. Cows were inseminated at the time of detection of heat after, following the second synchronization. The synchronization facilitated a distinct rise and then fall in P4 secretion characteristic of the oestrus cycle (Figure 1). However the PCM caused a decrease in P4 secretion which coincided with a decrease in pregnancy rate from 60% (6/10) in the control group to 40% and 20% for the 1 and 2 kg supplemented groups respectively. These changes were associated with a dosedependent increase in the linoleic acid content in milk (Simos et al. 1999). This study suggests that the provision of a source of linoleic acid to isocaloric diets decreases ovarian luteal cell function in the dairy cow. The challenge remains to determine at which level of the reproductive endorine axis this effect occurs (Staples et al. (1998). Simos, G.C., DellaVedova, J.J., Myung, K.H., Fleck, E., Gooden, J.M. and Wynn, P.C. (1999). Manipulation of bovine milk composition through supplementation with a protected cottonseed meal. Recent Advances in Animal Nutrition in Australia 12, 23A. Staples, P.R., Burke, J.M. and Thatcher, W.W. (1998). Influence of supplemental fats on reproductive tissues and performance of lactating cows. Journal of Dairy Science, 81, 856871. Figure 1 Effect of PCM on P4 levels in milk. Recent Advances in Animal Nutrition in Australia, Volume 12 (1999)