Effect of Zone Cooling on Milk Yield, Thyroid Activity and Stress Indicators

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Abstract
Ten lactating dairy cows were used to study the effect of limited zone cooling on milk yield, milk fat percentage, rectal temperature, respiration rate and thyroid activity. The 10 cows were paired, divided into 2 groups, control and zone cooled, and subjected to a switchback design with three 3 wk periods. Treated cows were cooled .apprx. 14 h a day by locking their heads in a plywood enclosure with an air supply of 23.5.degree. C. Control cows were on the opposite side of the same open shed without zone cooling. Cows were released to similar paddocks at night where sorghum silage was fed ad lib; alfalfa hay ad lib and concentrates according to production were fed during the day. Mean daily milk yields of the 2 groups were 20.97 kg zone cooled and 19.68 kg control. Milk fat percentage and thyroid activity were not altered by zone cooling. Respiration rate and rectal temperature decreased in zone cooled cows.

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