Author： Smith BL Collier AJ Lawrence RJ Towers NR
Publisher： Taylor & Francis Ltd
ISSN： 1176-0710
Source： New Zealand Veterinary Journal, Vol.32, Iss.4, 1984-04, pp. : 48-50
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Abstract
Clinical hypocalcaemia was associated with single doses of three oi more days` supply of zinc oxide to dairy cows for facial eczema control. Experimental hand dosing of a single dose of zinc oxide (40 and 120 mg Zn/kg b wt) to Jersey cows caused a significant drop in serum calcium concentration at 24 h followed by a rise to concentrations higher than controls at subsequent samplings over four days. At the highest zinc dose rate, 78% of serum calcium values were equal to or lower than the lowest control value at 24 h post dosing. Serum magnesium concentrations had a reciprocal relationship to the calcium levels at all samplings. Serum zinc concentrations were most elevated over the 48 h post dosing, returning to normal levels at the fifth day. Following the highest zinc dose milk yields were reduced by approximately 1.5 kg milk/cow/day for 48 h. Similar results were obtained when cows grazed pasture on which large amounts of zinc oxide had been sprayed.
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