Effect of solar radiation on dairy cattle behaviour, use of shade and body temperature in a pasture-based system

Our aim was to understand how protection from solar radiation influenced the behaviour and physiology of Holstein Friesian dairy cattle. We compared the behaviour and body temperature of pastured dairy cattle kept in 1of 4 treatments: no shade or free access to shade that blocked either 25, 50 or 99% of solar radiation (n = 3 groups per treatment, 3 animals/group). Within each group, cows were categorized as predominantly black, black and white or white in colour (n = 1 of each coat colour per group). Shade use increased with higher levels of protection from solar radiation (total shade use, 25%: 1.3 h, 50%: 3.0 h, 99%: 3.3 h/15.5 day-time h, S.E.M.: 0.22 h, P < 0.001). As average ambient solar radiation increased, total use of the shade structures increased (26 of 27 cows had a positive relationship between solar radiation and total use of shade structures, P < 0.001). This pattern was particularity apparent for the 50 and 99% treatments (P = 0.009). Cows were more likely to use the shade structures when ambient solar radiation levels were highest within a day, highlighting the importance of providing enough shade for all cows to simultaneously use this resource. Standing was the most common behaviour under shade (25%: 1.1 h, 50%: 2.7 h, 99%: 2.9 h/15.5 day-time h, S.E.M.: 0.21 h, P = 0.001). Treatments had no effect on time spent lying or grazing over 24 h (lying: no shade: 9.0 h, 25%: 9.1 h, 50%: 9.5 h, 99%: 8.8 h/24 h, S.E.M.: 0.33 h, P = 0.630; grazing: no shade: 9.0 h, 25%: 9.4 h, 50%: 9.1 h, 99%: 9.3 h/24 h, S.E.M.: 0.19 h, P = 0.231). Cows with more protection from solar radiation had lower minimum body temperature (no shade: 37.9 °C, 25%: 37.9 °C, 50%: 37.9 °C, 99%: 37.7 °C, S.E.M.: 0.05 °C, P = 0.004). Together, these results demonstrate that the degree of protection from solar radiation is an important design feature of effective shade for dairy cattle.