Abstract:
SODIUM STATUS OF STEERS GRAZING TROPICAL BOTHRIOCHLOA PASTURES R.M. MURRAY*, E. TELENI* and M.J. PLAYNE+ Many tropical pastures are very low in sodium (Playne 1970) yet few experiments have shown responses which could be attributed to supplementation of cattle with this element. Recently Murphy and Plasto (1973) have reported an unequivocal growth response to sodium chloride supplementation of grazing beef cows and their calves. This study reports the growth responses and saliva sodium levels for a group of four 2 year old Droughtmaster 'steers (group 1) grazing blue grass (Bothriochloa decipiens var. Cloncurriensis) dominant pastures known to be low in sodium (0.012%). These are compared with results for a further nine Droughtmaster steers (groups 2 and 3) grazing spear grass (Heteropogon contortus) .in combination with Townsville stylo (Stylosanthes humilis) which contained 0.046% and 0.112% sodium respectively. Five animals from the spear grass pasture (group 2) were then introduced to the blue grass pasture on 13.xii.74 and measurements of live weight and saliva sodium.made one and five weeks later. Saliva sodium levels (meq/l) saliva sodium:potassium ratios (g/g) and liveweight change (kg/d) of the steers during. the month preceding sampling are shown in the table. The cattle grazing the blue grass pasture had low salivary sodium and elevated salivary potassium levels compared with the cattle grazing spear grass. The animals introduced to the blue grass from the spear grass Townsville stylo pasture showed low salivary sodium levels within one week and maintained these low levels throughout the following month. Between animal variations were large. Liveweight change however was\ unaffected by the low sodium status. Hennessy (1970) has shown that cattle can adapt rapidly to conditions of low sodium intake and was unable to demonstrate any liveweight response to sodium chloride supplementation of growing cattle, despite low saliva sodium levels. It would be wise therefore, to thoroughly examine the situation before promulgating to the industry the widespread use of salt supplements based on low saliva sodium levels alone. REFERENCES Hennessy, D.W. (1970). M.Rur.Sc. Thesis. University of New England. Murphy, G.M. and Plasto, A.W. (1973). Australian Journal of experimental Agriculture and animal Husbandry. 13:369. Playne, M.J. (1970). Australian Journal ofyxperimental Agriculture and animal Husbandry. 10:32. * Department Townsville, + C.S.I.R.O., Townsville, of Tropical Veterinary Science, James Cook University, Q. 4811. Division of Tropical Agronomy, Davies Laboratory, Q. 4811. 9P