The effect of coal mine pit water on the productivity of cattle. I. Mineral intake, retention and excretion and the water balance in growing steers

Abstract

Coal mine pit water contains high concentrations of inorganic sulfur (S) along with lesser concentrations of calcium (Ca), magnesium (Mg), sodium (Na), and chloride (C1-). In the Bowen Basin of Central Queensland beef cattle grazing adjacent to mine sites may ingest this water. This study examined the effect of diluted coal mine pit water on the intake, routes of excretion, digestibility, and retention of nitrogen and minerals in steers, and also measured the changes in the concentration of electrolytes and metabolites in blood plasma and urine, and the water content, within the animals. Twelve growing steers weighing 352rt7 kg (mean ¦.s.e.m.) were divided into 2 groups of 6 and randomly allocated 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 of feed, Medicago sativa hay, was fixed at 5.5 kg dry matter/day. Following a 35-day adaptation to the final concentration of pit water (2000 mg sulfate/L) an 8-day collection for digestibility and mineral retention was undertaken. The ingestion of high mineral loads in diluted coal mine pit water did not significantly (P > 0.05) alter water and feed intake and organic matter digestibility of the diet. The percentage increase in total mineral excretion for steers consuming pit water compared to animals drinking town water was S 90, Ca 39, Mg 40, Na 162, and C1- 31. There was no significant (P > 0.05) difference between drinking water treatments in the retention of nitrogen. S, Ca, Mg, Na, and C1-. The concentrations of urea-nitrogen, minerals (apart from Mg), and thiamin in blood plasma remained similar for both treatments. The concentration of Mg in blood plasma was significantly (P < 0.05) higher in steers receiving pit water (22.4 mg/L) than in steers receiving town water (19.9 mg/L). Indicators of dehydration and movement of body solutes in steers were not influenced by treatment. The findings demonstrate the ability of cattle to maintain their water and solute homeostasis for at least 46 days when consuming high concentrations of minerals sourced from diluted coal mine pit water. The mechanisms with which cattle achieve this are discussed.