Maintenance energy requirements of dairy cows. (Abstract)

Abstract

5A Maintenance energy requirements of dairy cows J.L. Corbett1 and M. Freer2 1 2 School of Rural Science and Agriculture, Animal Science, University of New England, Armidale NSW 2351 CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601 jcorbett@metz.une.edu.au Agnew et al. (2000) and Kebreab et al. (2003) report that cows in recent years yielding up to 160 MJ milk/d (51.6 kg 4% fatcorrected milk, FCM) had a mean metabolizable energy requirement for maintenance (MEm) of 0.63 MJ/kgW0.75. Reasons of Agnew et al. (2000) for that being 30% greater than the AFRC (1993) value of 0.48 MJ/kgW0.75 include a high fibre diet, which was not given to the cows studied, and grazing activity, though there was little grazing in these studies. Agnew et al. (2000) and Yan et al. (2003) appear to regard improved genetic merit as the primary cause. There is some variation among Bos taurus breeds in their MEm which is about 17% greater than for B. indicus (SCA 1990); it is improbable that it could be a further 30% greater for cows improved genetically. We suggest the high MEm is because of increases in energy expenditures in the body to support increased production from increased intakes. Yan et al. (1997) measured the fasting heat productions (FHP) of cows fed near ad libitum before fast. The mean FHP was 0.453 MJ/kgW0.75 (equivalent to 0.62 MJ ME) and it is known that values are greater than when the fast is preceded by feeding at maintenance level (L = 1). For feeds with ME/kg DM similar to those in the recent studies, the SCA (1990) MEm at L = 1 for B. taurus is 0.537exp(0.03A) MJ/kgW0.75, where A is age in years (maximum 6). Increases in support metabolism for production from increased intakes are allowed for in MEm by adding 0.1 of the ME used directly for production. Simple calculation by SCA (1990), and by AFRC (1993), of ME required in early lactation does not allow for contributions of energy from body tissues to milk synthesis; that the synthesis then is not wholly from dietary energy is allowed for by GrazFeed (Freer et al. 1997; Table 1). Yan et al. (2003) found that the SCA system gave better predictions of total energy requirement than the UK, most European, and the USA systems. AFRC (1993). Energy and Protein Requirements of Ruminants. CAB International, Oxon, UK. Agnew, R.E. and Yan, T. (2000). Impact of research on energy feeding systems for dairy cattle. Livestock Production Science 66, 197215. Freer, M., Moore, A.D. and Donnelly, J.R. (1997). GrazPlan: Decision support systems for Australian grazing enterprises. II.The animal biology model for feed intake, production and reproduction and the GrazFeed DSS. Agricultural Systems 54, 77126. Kebreab, E., Francis, J., Agnew, R.E., Yan, T., Dhanoa, M.S., Dijkstra, J. and Beever, D.E. (2003). Alternatives to linear analysis of energy balance data from lactating dairy cows. Journal of Dairy Science (in press). SCA (1990). Feeding Standards for Australian Livestock: Ruminants. Standing Committee on Agriculture and CSIRO, Melbourne, Australia. Yan, T., Gordon, F.J., Ferris, C.P., Agnew, R.E., Porter, M.G. and Patterson, D.C. (1997). The fasting heat production and effect of lactation on energy utilization by dairy cows offered foragebased diets. Livestock Production Science 52, 177186. Yan, T., Agnew, R.E., Murphy, J.J., Ferris, C.P. and Gordon, F.J. (2003). Evaluation of different energ y feeding systems with production data from lactating dairy cows offered grass silagebased diets. Journal of Dairy Science 86, 14151428. Table 1 Metabolizable energy for maintenance (MEm) of a 650 kg cow 4 years old at day 60 of lactation calculated without (SCA) and with (GrazFeed) energy from body used for milk. MEm (MJ/kgW 4% FCM yield kg/d 20 30 40 50 SCA 0.55 0.59 0.63 0.67 0.75) GrazFeed 0.51 0.54 0.58 0.60 Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)