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