A trial at AgResearch Ruakura, evaluating two different methods of administering zinc++(Zn) salts to protect cows from facial eczema, was carried out in lactating dairy cows to study the variation in concentrations of blood Zn++. The treatments were: continuous supply of zinc sulphate (ZnSO4) through water troughs (n = 10 cows), versus daily oral drenching with zinc oxide (ZnO) (n = 10 cows). Responses in daily milk yields, and concentrations of Zn++in blood were recorded twice weekly over four weeks for each cow. The ZnSO4trough treatment took ten days for blood Zn++concentrations to equilibrate, after which the sampling-day average ranged from 20–26 μmol/L. Between-cow repeatability was 0.42 ± 0.15. The daily ZnO treated cows equilibrated after drenching for three days. Average blood Zn++concentrations then ranged from 24–29 μmol/L. Between-cow repeatability was 0.44 ± 0.17. Dailymilk yields did not differ significantly between treatments. Target ranges for blood Zn++concentrations to provide protection against facial eczema in lactating dairy cows of 18–34 μmol/L were published 26 years ago. These may need to be re-assessed, with changes in breed composition and increases in milk yield over that time within the national herd.

CA, Morris, and SM Hickey

Proceedings of the New Zealand Society of Animal Production, Volume 73, Hamilton, 171-174, 2013
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