Dairy cows prefer shade that offers greater protection against solar radiation in summer: Shade use, behaviour, and body temperature

There is considerable evidence that shade is a valuable resource for cattle in summer, but less is known about the important design features of effective shade. The aim of this experiment was to investigate if lactating dairy cows have a preference for shade that offers greater protection against solar radiation. Shade was provided by wooden structures covered with shade cloth that blocked 25, 50 or 99% of solar radiation. Nine groups of Holstein-Friesian cows (27 animals in total, 3 animals/group) were exposed to three treatment combinations: pair-wise simultaneous presentation of shade cloth that blocked: (1) 50 and 99%, (2) 25 and 50%, and (3) 25 and 99% of solar radiation. Cows were exposed to each combination in a cross-over design (2 d/combination). Shade use and time budgets were recorded during the hottest part of the day (10:00-17:00 h). Within each group, cows were categorised as predominantly black, white, or black and white in colour (one of each coat colour/group) in order to investigate the interaction between coat colour and treatment choice. Cows preferred shade cloth that blocked greater amounts of solar radiation in two of the combinations (99% versus 25%: 72.3% time spent in the 99% option, P < 0.001, S.E.: 3.9%: 50% versus 25%: 72.0% time spent in the 50% option, P < 0.001, S.E.: 3.5%), but showed no preference for shade cloth that blocked 50 or 99% of solar radiation when these two options were presented simultaneously (49.8% time spent in the 99% option, P = 0.509, S.E.: 5.3%). Neither coat colour nor weather conditions influenced preference for shade type. Cows spent more time in shade on days with higher solar radiation levels (P < 0.001, slope: 0.04%, S.E.: 0.01%) and higher ambient air temperature (P = 0.021, slope: 2.63%, S.E.: 0.02%). Mean body temperature increased with increasing temperature-humidity index (P = 0.014, slope: 1.9%, S.E.: 0.7%), heat load index (P = 0.009, slope: 0.6%, S.E.: 0.2%) and ambient air temperature (P = 0.065, slope: 2.1%, S.E.: 1.1%). In conclusion, cows preferred shade that provided more protection from solar radiation (50 and 99% blockage versus 25%) and showed behavioural and physiological changes associated with increased heat load. (C) 2008 Elsevier B.V. All rights reserved.