Physiological and Production Responses of Dairy Cattle to a Shade Structure in a Subtropical Environment

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Abstract
Lactating cows (116) were assigned randomly to shade or no shade treatments during the summers of 1974 and 1975. Shade structure was 9.1 .times. 24.4 m with an insulated metal gable roof and floor of reinforced concrete. Feed and water were available under the structure, and cows had free access to adjacent bermudagrass sod. Black globe temperature was the climatological response that differed among treatments (shade = 28.4.degree. C, no shade = 36.7.degree. C). Respirations/min (54 < 82) and rectal temperatures (38.9.degree. C < 39.4.degree. C) were lower for shade cows. Least squares means for milk yield, considering variability due to treatment, year, treatment-year, breed, breed-treatment, year-breed, year-breed-treatment, cows in year-breed-treatment, week of experiment, and days pregnant, were 16.6 and 15.0 kg/day for shade and no shade, a 10.7% effect. Lactation curves were heterogenous. Conception rates were 44.4% (54 services) and 25.3% (75 services) for shade and no shade. Results suggest improvement in reproduction and lactation from providing shade structure.