The provision of zinc sulphate in water for dairy cattle to prevent facial eczema: can it work?

AIMS: To evaluate, in a sample of cows on a New Zealand dairy farm, whether different methods of oral supplementation with zinc were effective in raising serum Zn concentrations ≥ 18 μmol/L, the target threshold for protection from facial eczema. METHODS: O was added, with the full dose at Week 2, and continuing for the rest of the facial eczema season (approximately 16 weeks). Semi-quantitative analysis of the water consumption of the group over the previous day(s), plus subjective impressions of the effect of the current weather on the cows' drinking behaviour, were used to adjust the quantity of Zn mixed with the current day's water supply. For all scenarios, serum samples were taken periodically from study cows to monitor the serum Zn concentrations. RESULTS: Daily drenching increased serum Zn concentration: 12/15 cows (80%; 95% CI = 55-93%) reaching ≥ 18 μmol/L on Days 3 and 6. Under trough dosing, the half dose achieved a mean serum Zn concentration of 20.7 μmol/L and up to 60% (95% CI = 26-82%) of cows ≥ 18 μmol/L: at full dose the mean concentration was 16.3 μmol/L with 30% of cows (95% CI = 7-65%) ≥ 18 μmol/L. Supplementation using the dosing pump did not increase mean serum Zn concentration to ≥ 18 μmol/L at any timepoint (maximum proportion of cows ≥ 18 μmol/L: 44%). CONCLUSIONS AND CLINICAL RELEVANCE: Apart from individual dosing, Zn supplementation via drinking water did not reliably increase serum Zn concentrations. This is probably related to the great variability in both group and individual water consumption. Water-based Zn supplementation should not be recommended to prevent facial eczema.