Artificial Shade Effects in the Performance and Physiology of Dairy Heifers in Pasture

摘要

A more accurate accounting of the effect of environment on milk production or growth rate is needed to diagnose performance problems and to make decisions about facility design and pasture systems. This work was undertaken to study the effects of thethree roofed shading types during summer in Brazil tropical conditions on some physiological functions related to the heat dispersing process like rectal temperature, respiratory frequency, and infrared skin temperature, as veil as the body weight gain of growing dairy heifers in pastures. Sixteen Holstein heifers and sixteen Holstein x Jersey cross heifers (initially weighing 263 ±66 kg) were kept for a 142-day period, during the hot times of the day in sixteen adjacent pens, in four randomized blocks. The roof types -were: galvanized steel, asbestos cement, and polypropylene shade cloth graded '80% shade'. The pens were shaded with a roof (4 m high), allowing for 4.0 nf of shade/heifer. All animals -were submitted to identical management. The results obtained showed differences in the treatments (p<0.00l) for respiratory rate, rectal temperature, and skin temperature, but no difference for body weight gain. The best shade was asbestos cement, the galvanized steel was the second best, and cloth wasthe least satisfactory.