title: Hypocalcaemia associated with high dose rates of zinc oxide to lactating dairy cows.
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.
authors.forename: B L
authors.initials: BL
authors.lastname: Smith
authors.forename: A J
authors.initials: AJ
authors.lastname: Collier
authors.forename: R J
authors.initials: RJ
authors.lastname: Lawrence
authors.forename: N R
authors.initials: NR
authors.lastname: Towers