Microclimatic characterization of natural and artificial shading and its influence on the physiological and behavioural responses of Holstein cows

This study aimed to evaluate the microclimatic conditions of natural shading provided by Ipês (Handroanthus heptaphyllus [Vell.] Mattos), and of an artificial shading structure characterized by the combination of an aluminized net on the outside and a black polypropylene net on the inside. In addition, their effects were analysed with respect to the physiological and behavioural responses of Holstein cows kept at pasture in a tropical climate. Two paddocks were used, one with trees and the other with trees and an artificial shade structure. Eight multiparous cows were evaluated over 20 non-consecutive days and selected according to their predominant coat colour: four with predominantly white coats and four with predominantly black coats. The experimental days were classified as very hot, with radiation above 625 Wm-2; and hot days, with radiation between 300 and 625 Wm-2. The mean radiant temperature (°C), the radiant heat load (Wm-2) and the black globe humidity index were calculated. The mean radiant temperature for artificial shading was lower for all days (P < 0.05), with values below 30°C during daylight hours. The radiant heat load was lower under the artificial shading structure regardless of the day (P < 0.05), with values below 470 Wm-2. When compared microclimatically with natural shading, artificial shading was more efficient (P < 0.05) in reducing mean radiant temperature and radiant heat load. Although behavioural variation (P < 0.05) was observed, these results were related to the difference in coat pattern. Animals with predominantly black coats grazed in the early morning hours and sought protection as thermal comfort levels rose.