Production and Physiological Responses of Lactating Holstein Dairy Cows to the Provision of Shade in Sub-Tropical Zimbabwe.
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The objective of this study was to establish production and physiological benefits of shade provision to lactating Holstein cows under hot summer conditions in Zimbabwe. Different shading materials providing shade at different levels were used so that a recommendation could be made as to the effectiveness of the shading materials in providing a comfortable thermoneutral micro-environment during periods of heat stress. Three experiments were conducted at the University of Zimbabwe Farm, Harare, Zimbabwe. The Holstein dairy breed which is the main dairy breed making the University of Zimbabwe Farm dairy herd was used in Experiments 1 and 2 whose main objectives were centered on evaluating production and physiological responses of lactating cows to different levels of shading during periods of intense solar radiation and high ambient temperatures. Three levels of shading were provided: 100%, 80% and 30% shade. Experiment 3 involved a comparison of radiation balances under the three shading materials which were used in Experiment 2 which were; Hessian 30% shade cloth, Hessian 80% shade cloth and corrugated iron sheets. Cows under corrugated iron sheets (100% shade) had significantly (P < 0.05) lower skin surface temperature, respiration rate, rectal temperature and water intake compared to those under Hessian 30% shade cloth (Experiment 1). Milk yields increased significantly (P < 0.05) in cows under 100% shade compared to those under 30% shade. Skin surface temperature of cows under Hessian 80% shade cloth were not significantly (P > 0.01) different from skin surface temperatures of cows under corrugated iron sheets (Experiment 2). In Experiment 3, corrugated iron sheets completely cut off direct solar radiation but emitted the highest amount of thermal radiation. These results indicate that shade provision to lactating cows during the summer is of great benefit. In addition, corrugated iron sheets provide 100% shade but they release a significant amount of thermal radiation and considering this substantial amount of direct long wave radiation the Hessian 80% shade cloth can be used as an effective alternative shading