EFFECT OF COAL-MINE PIT WATER ON THE PRODUCTIVITY OF CATTLE .2. EFFECT OF INCREASING CONCENTRATIONS OF PIT WATER ON FEED-INTAKE AND HEALTH

The effect of drinking high mineral content coal mine pit water on the health and growth of yearling tropically adapted steers was investiga ted. Steers consumed town water (similar to 30 mg sulfate/L) or diluti ons of pit water, which at the highest concentration contained (mg/L) 4000 sulfate as well as 3082 chloride, 328 calcium, 562 magnesium, 260 0 sodium, and other minerals at lesser concentrations (total dissolved solids, 8600 mg/L). The growth and performance of the steers a ere me asured as average daily weight gain, dry matter intake, faecal dry mat ter content, and water intake. Health was assessed using haematologica l indices (packed cell volume, haemoglobin, and others) and on randoml y selected animals, by complete post mortem haematological and biochem ical analysis. Consumption of diluted pit water of up to 2000 mg sulfa te/L, if introduced gradually, did not result in a reduction in dry ma tter or water intake. Significant interactions (P < 0 . 05) occurred b etween rate of introduction and plane of nutrition in affecting weight gain, whereby weight gains on pit water were marginally greater when treatment was introduced abruptly. Plane of nutrition was the main eff ect in determination of packed cell volumes, where low plane of nutrit ion led to higher values. Interactions of time on pit water treatment with rate of introduction or nutrition in affecting packed cell volume were statistically significant (P less than or equal to 0 . 006) but small in magnitude (1-2%): and hence unlikely to be biologically signi ficant since averages remained within the normal range for the age gro up. Pit water treatment did not compromise the animals' health at 2000 mg sulfate/L, as assessed by visual veterinary and histopathological examinations of tissues taken at autopsy. When the concentration of pi t water was increased to 4000 mg sulfate/L, dry matter intake was depr essed by 14% and water intake was decreased by up to 40%, increasing s lightly with longer time on treatment. Under the conditions of this ex periment, beef steers can drink coal mine pit water containing up to 2 000 mg sulfate/L (4000-6000 mg/L of total dissolved solids) without su ffering ill effects, provided that it is introduced gradually. The stu dy therefore provides evidence that the recommendation of 1000 mg sulf ate/L as the maximum concentration in livestock drinking water may be too conservative for steers if favourable conditions exist.