Herd Dominance Influences Dairy Cows' Use of Heat Abatement Resources in a Silvopastoral System.

The social category of dairy cows within a herd may influence their access to essential heat abatement resources. We evaluated how dominant, intermediate, and subordinate cows used shade and water in a silvopastoral system. Thirty-nine lactating Jersey cows were observed in a replicated study. Cows had unrestricted access to natural shade and a water trough. Microclimatic conditions and cow behaviors were recorded, and social rank was determined. Sunny areas promoted potential thermal discomfort for the cows, with higher heat load (on average 580.7 W/m2) than shaded areas (on average 438.6 W/m2). Intermediate (IRR: 2.07) and subordinate (IRR: 1.63) cows were more likely (p < 0.001) to visit the water trough than dominant cows. The odds of drinking water decreased by 13% (p < 0.001) for each hour that passed throughout the day. In contrast, the odds of using shaded areas increased by 7% (p < 0.001) for each increase in hour unit. Although all cows used the shaded areas at some point, they generally spent more time standing than lying down in the shade. Social category and hour influenced (p < 0.001) the behaviors in the shaded areas, with dominant cows more likely to engage in lying behaviors such as idling and rumination. In conclusion, our study demonstrated that cows' social category and thermal environment influenced the use of shade and drinking water. Although the overall pattern of resource use increased with rising thermal load, the proportion of use varied according to social category. Ensuring multiple or alternative resources may help meet the needs of cows across social ranks and improve thermal comfort during heat stress periods.