A defensible maximum for inorganic sulfate in drinking water of cattle.

Twelve Hereford-Angus weanling heifers were used in a split:plot design incorporating a randomized complete block to determine physiological effects of subtoxic concentrations of inorganic sulfate in drinking water. Treatments were tap-water (110 mg/liter sulfate), 1,250 rag/liter sulfate and 2,500 rag/liter surface. The sulfate was added to the tap water as sodium sulfate. The sulfate-waters did not affect feed consumption, water consumption or growth during the 90-day experiment. No overt toxicity was observed. Heifers drinking sulfate-water had tendencies to accumulate methemoglobin and sulfhemoglobin without affecting total hemoglobin. Sulfate loading did not induce diuresis although heifers drinking 2,500 mg/liter sulfate-water increased renal filtration of sulfate by 37.7% and decreased renal reabsorption of this ion by 23.7%. Therefore, in these animals the percentage of filtered sulfate reabsorbed was decreased by 44.8%. The heifers were subsequently used in a taste response experiment in which they were offered either sodium chloride or sodium sulfate in a twochoice preference situation. The choice was the salt solution or tap-water. The salts were added to tap-water in increasing but estimated equal anionic concentrations in six increments from 275 to 4,400 mg/liter of anion. The animals discriminated against drinking water containing 1,620 mg/liter chloride or 2,018 rag/liter sulfate. Concentrations at the estimated rejection threshold were 5,524 and 3,317 rag/liter for chloride and sulfate, respectively. On a molar basis, discrimination and rejection thresholds for suffate were 21.0 and 34.5 raM, respectively. Those for chloride were 45.6 and 155.6 mMolar. Apparently, sulfate was more unpalatable than chloride when compared on an equimolar basis. It appears that these heifers were able to tolerate 2,500 rag/liter sulfate in their drinking water without adverse effects, and that this concentration of sulfate represents a safe tolerance concentration. (