Abstract:
Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 PHOSPHORUS KINETICS IN GRAZING BRAHMAN-CROSS COWS D.B. COATESA, J.H. TERNOUTHB, C.P. MILLERC and S.J. WHITE B * CSIRO Division of Tropical Crops and Pastures, Davies Laboratory, PMB, PO Aitkenvale, Qld 48 14 B Dept of Agriculture, The University of Queensland, St Lucia, Qld 4072 'Dept of Primary Industries, PO Box 1054, Mareeba, Qld 4880 The phosphorus (P) requirements of growing cattle consuming roughage diets as recommended by most authorities are overestimated (Ternouth et al. 1996) due primarily to the use of a low P absorption coefficient or a high net requirement for maintenance (mainly endogenous faecal P) in the factorial calculation. This paper presents preliminary results from an investigation of the P requirements of breeding cows in a grazing trial at Springmount, near Mareeba, in north Queensland. The treatments and cattle used have been described by Miller et al. (1996). Experiments to measure the P kinetics of 4 cows from within each of 4 treatment groups were carried out during late pregnancy (September), lactation (February) and 8 weeks after weaning (May). The procedures have been described by Coates and Temouth (1992) and involved the measurement of dietary P concentration and DM digestibility (using oesophageal fistulated steers), faecal output (chromic oxide capsules), and endogenous faecal P (using 32P). Results for the first draft of cows (1993/94) are presented (Table 1). Table 1. Phosphorus kinetics of cows in response to soil P and supplementation . COATES, D.B. and TERNOUTH, J.H. (1992). J. Agric. Sci., Camb. 119: 401-9. MILLER, C.P., FITZPATRICK, L.A., WHITE, S.J., COATES, D.B. and TERNOUTH, J.H. (1996). Proc. Aust. Sot. Anim. Prod. 21: 355. TERNOUTH, J.H., BORTOLUSSI, G., COATES, D.B., HENDRICKSEN, R.E. and MCLEAN, R.M. (1996). J. Agric. Sci., Camb. (in press). 380