Intake of zinc sulphate in drinking water by grazing beef cattle

Abstract

Addition of zinc sulphate to drinking water was evaluated as a possible technique for protecting cattle against the facial eczema toxin, sporidesmin. To be reliable the zinc intake from water should be reasonably predictable and should supply enough zinc to protect against the toxin without providing excessive and potentially toxic amounts of this metal. The daily water intakes of 48 young grazing beef cattle offered water containing either 0, 0.28, 0.56 or 1.12 g ZnSO₄.7H₂O/l were increased for 8 weeks in February–April 1976. Intakes were not affected by the presence of zinc sulphate but were reduced after rain. After rain, Pithomyces chartarum spores increased to potentially dangerous levels on paddocks not sprayed with fungicide. No evidence of liver damage was found in any cattle. No signs of zinp toxicity appeared in the cattle which drank water containing zinc; instead an unexplained weight gain advantage was found in these cattle compared with animals drinking untreated water. Using tritium oxide, individual intakes of drinking water accounted for 92.4% of the water disappearing from the troughs. A wide variation, approximately 4-fold, was found in individual intakes of drinking water. Because of the varied and unpredictable intakes of drinking water this method of supplying zinc to cattle cannot be recommended as reliable for facial eczema control.