Hypocalcaemia associated with high dose rates of zinc oxide to lactating dairy cows |
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Authors: | BL Smith AJ Collier RJ Lawrence NR Towers |
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Institution: | 1. Invermay Animal Health Laboratory , Private Bag, Mosgiel;2. lnvermay Agricultural Research Centre , Private Bag, Mosgiel |
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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 h 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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