The mineral status of cattle grazing tagasaste

Abstract

Animal Production in Australia 1998 Vol. 22 THE MINERAL STATUS OF CATTLE GRAZING TAGASASTE N.J. EDWARDS A B A,B and G.M. ALLEN A Animal Science Group, Faculty of Agriculture, The University of Western Australia, Nedlands, WA 6097 Current Address: CSIRO Division of Animal Production, Private Bag, PO Wembley, WA 6014 The mineral status of sheep and cattle in various tagasaste (Chamaecytisus proliferus) grazing systems in Western Australia (Edwards et al. 1996) has received little attention despite indications of trace element deficiencies (McGowan et al. 1988; Borens and Poppi, 1990; Wiley et al. 1994). Advice on mineral supplementation is currently based on typical mineral levels in this leguminous shrub and it is essential that measures be made of the actual mineral status of animals, as in this work. The aim was to develop strategies for mineral supplementation. As part of an experiment at Dunmar , near Badgingarra 230 km north of Perth, to investigate the response of tagasaste to phosphatic fertiliser, we examined the seasonal variation in mineral status of cattle with continual access to tagasaste. Twenty six, 9 month old mixed breed heifers weighing 186 � 2.6 kg were introduced in pairs to 13 x 2.6 ha plots of tagasaste in May 1995. Blood (via venipuncture), liver (via biopsy) and saliva samples were collected from the animals in May, August and November 1995 and January and April 1996. Plasma was analysed for Mg, Ca, phosphate, sulphate, Cu and Zn, erythrocytes for glutathione peroxidase (GSHPx) activity, liver for Cu and Co levels and saliva for Na and K concentration. No mineral supplements were offered to the animals during the experiment. Table 1. Seasonal concentrations of macro- and micr o-minerals in the blood, liver and saliva of cattle grazing tagasaste (values in brackets indicate % of animals below normal range) Normal range Blood Mg (mmol/L) Ca (mmol/L) Phosphate (mmol/L) Sulphate (mmol/L) GSHPx (IU/g Hb) Cu (mmol/L) Zn (mmol/L) Liver Cu (mg/g fresh) Co (mg/g fresh) Salivary Na:K (molar ratio) 0.7-1.0 2.0-2.5 1.2-2.3 N.A. >30 0.6-1.1 0.8-1.3 >15 >0.02 >14 May 95 Aug 95 Nov 95 0.92 2.61 2.15 0.41 (67) 66 0.97 0.93 (21) 31.1 (16) 0.04 (36) 13.0 (13) Jan 96 0.97 2.35 1.84 0.42 (57) 56 0.75 0.89 (23) 38.5 0.04 (9) 8.3 (37) Apr 96 0.98 2.39 1.70 (17) 0.29 (87) 73 0.77 (13) 0.98 31.5 0.05 6.2 (43) s.d. 0.08 0.11 0.35 0.29 37.6 0.14 0.14 12.3 0.02 6.0 0.95 0.95 2.35 2.48 2.04 2.39 0.59 (44) 0.76 (15) N.D. 175 0.92 0.83 0.99 0.88 (31) N.D. N.D. N.D. 19.7 (27) 0.02 (54) 8.2 (46) N.A. = Not Available; N.D. = Not Determined Mean concentrations of most minerals were within normal ranges expected by the Agriculture WA Animal Health Laboratories, but in many individual animals low values for blood sulphate (based on sheep values) and zinc, liver copper and cobalt, and salivary Na:K ratio were detected. Concentrations of most minerals varied between seasons, with blood phosphate, sulphate and GSHPx peaking in August (winter). These data are from only one site through a single year but they support the assertions of Wiley et al. (1994) and McGowan et al. (1995) that low levels of S, Na, Cu, Zn, Co and Se could result in deficiencies in animals grazing tagasaste. Further work is needed to establish whether the results apply at other sites, in different years, and when different inter-row species are available. We thank Drs Jeremy Allen, Ray Ansotegui, Pauline Roberts and Marion Seymour for the liver biopsies and Gerard Smith for sample analyses. Martindale Pty Ltd generously made both site and animals available and the financial assistance of the Cattle Industry Compensation Fund of WA is gratefully acknowledged. BORENS, F.M.P. and POPPI, D.P. (1990). Anim. Feed Sci. Technol. 28, 275-92. EDWARDS, N.J., OLDHAM, C.M., ALLEN, G.M., MCNEILL, D.M. and TUDOR, G. (1996). In Tagasaste Review Workshop, pp. 61-99 (Faculty of Agriculture, University of Western Australia). McGOWAN, A.A., ROBINSON, I. and MOATE, P. (1988). Proc. Aust. Soc. Anim. Prod. 17, 230-3. McGOWAN, A.A., MATHEWS, G.L. and MOATE, P.J. (1995). Aust. J. Exp. Agric. 35, 51-4. WILEY, T., OLDHAM, C.M., ALLEN, G.M. and WIESE, T. (1994). Tagasaste. Bulletin 4291, Department of Agriculture, Western Australia. 380