Bone metabolism markers as indicators of phosphorus deficiency in breeding cows

Abstract

Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 BONE METABOLISM MARKERS AS INDICATORS OF PHOSPHORUS DEFICIENCY IN BREEDING COWS S. J. WHITE A , C. P. MILLER B and J.H. TERNOUTHA * Dept of Agriculture, University of Queensland, St. Lucia, Qld 4072 B Dept of Primary Industries, P.O. Box 1054, Mareeba, Qld 4880 Cattle in many areas of northern Australia graze low phosphorus (P) pastures, resulting in P deficiency and reduced productivity. Bone is the major reserve of P in the body and, during P deficiency, bone metabolism may be altered to regulate circulating P concentrations. This project seeks to evaluate two bone metabolism markers as indicators of P deficiency and reserve P depletion. Samples were collected in September 1994 (mid-dry), February (early wet) and May (late wet) 1995 from 8 cows in each of 3 unsupplemented treatment groups as described by Miller et al. 1996. Plasma inorganic phosphorus (Pip) concentration was measured by calorimetry of deproteinated plasma (Fiske and Subbarow, 1925). Osteocalcin (OC) concentration, a marker of bone formation, was measured in plasma by radioimmunoassay (in-house; Institute of Medical and Veterinary Science, Adelaide). Deoxypyridinoline (DPD) concentration, a marker of bone resorption, was measured in urine by enzyme linked immunosorbent assay (Metra Biosystems), and is expressed as a ratio to creatinine (CTN) concentration (Beckman Synchron), with no allowance for energy intake. Table 1. Bone metabolism markers of breeding cows in response to soil P level, season and physiological status Medium P cows had PIP concentrations indicative of adequate P status (McCosker and Winks 1994) during all seasons. Low and very low P cows had PiP concentrations indicating adequate P status during the dry season, but P status was deficient at other times. Concentrations of OC followed a similar pattern to Pip, with no difference in concentration between treatment groups in the dry season. During the wet season medium P cows tended to have higher OC than low and very low P cows. The seasonal changes in OC suggest that less bone formation occurred in the wet season, during and shortly after lactation. Excretion of DPD was very variable within groups, and did not vary significantly between treatments or seasons. The PiP data strongly suggests that low and very low P cows were in negative P balance in the wet season, during and shortly after lactation. The marker results suggest that bone formation rather than bone resorption is affected by negative P balance. Similar results have been obtained from P kinetic studies in breeding ewes (Budhi and Temouth 1996). BUDHI, S.P.S. and TERNOUTH, J.H. (1996). Aust. J. Exp. Agric. (in press). FISKE, C.H. and SUBBAROW, Y. (1925). J. Biol. Chem. 119: 375-400. McCOSKER, T.H. and WINKS, L. (1994). 'Phosphorus nutrition of beef cattle in northern Australia'. QI94012 (Department of Primary Industries: Queensland). MILLER, C.P., FITZPATRICK, L., WHITE, S-J., COATES, D.B. and TERNOUTH, J.H. (1996). Proc. Aust. Sot. Anim. Prod. 21: 355. 439