THE EFFECT OF COAL-MINE PIT WATER ON THE PRODUCTIVITY OF CATTLE .1. MINERAL INTAKE, RETENTION, AND EXCRETION AND THE WATER-BALANCE IN GROWING STEERS

Coal mine pit water contains high concentrations of inorganic sulfur ( S) along with lesser concentrations of calcium (Ca), magnesium (Mg), s odium (Na), and chloride (Cl-). In the Bowen Basin of Central Queensla nd beef cattle grazing adjacent to mine sites may ingest this water. T his study examined the effect of diluted coal mine pit water on tile i ntake, routes of excretion, digestibility, and retention of nitrogen a nd minerals in steers, and also measured the changes in the concentrat ion of electrolytes and metabolites in blood plasma and urine, and the water content, within the animals. Twelve growing steers weighing 352 +/-7 kg (mean+/-s.e.m.) were divided into 2 groups of 6 and randomly a llocated to 2 treatments: town water (low mineral content) or diluted coal mine pit water containing about 2000 mg sulfate/L, together with (approx. mg/L) Ca (190); Mg (260), Na (1300), and Cl- (1580). Intake o f feed, Medicago sativa hay, was fixed at 5.5 kg dry matter/day. Follo wing a 35-day adaptation to the final concentration of pit water (2000 mg sulfate/L) an 8-day collection for digestibility and mineral reten tion was undertaken. The ingestion of high mineral loads in diluted co al mine pit water did not significantly (P > 0.05) alter water and fee d intake and organic matter digestibility of the diet. The percentage increase in total mineral excretion for steers consuming pit water com pared to animals drinking town water was S 90, Ca 39, Mg 40, Na 162, a nd Cl- 31. There was no significant (P > 0.05) difference between drin king water treatments in the retention of nitrogen, S: Ca, Mg, Na, and Cl-. The concentrations of urea-nitrogen, minerals (apart from Mg), a nd thiamin in blood plasma remained similar for both treatments. The c oncentration of Mg in blood plasma was significantly (P < 0.05) higher in steers receiving pit water (22.4 mg/L) than in steers receiving to wn water (19.9 mg/L). Indicators of dehydration and movement of body s olutes in steers were not influenced by treatment. The findings demons trate the ability of cattle to maintain their water and solute homeost asis for at least 46 days when consuming high concentrations of minera ls sourced from diluted coal mine pit water. The mechanisms with which cattle achieve this are discussed.