Social hierarchy influences dairy cows’ use of shade in a silvopastoral system under intensive rotational grazing

Abstract

The aim of this study was to evaluate the relationship between thermal comfort indicators and social hierarchy, and cows' location (shade or sun) and their diurnal behaviors in a silvopastoral system of a subtropical climate, covering the four seasons. We measured microclimatic variables (air temperature, relative humidity, wind speed, soil surface temperature) and cows’ behaviors in two areas (shaded and sunny), as well as the influence of social hierarchy (dominant, intermediate, and subordinate) on cows' location (shade or sun). In addition, we determined the black globe-humidity index (BGHI) and radiant heat load (RHL) for both areas. Air temperature, wind speed, and soil surface temperature were lower in shaded areas, and relative humidity lower in the sunny areas (p < 0.05). The shaded areas provided on average a 23% RHL reduction in cold seasons (autumn and winter), and 26% in hot seasons (spring and summer). For cows of all social categories the odds of drinking water decreased (p < 0.001) for each additional BGHI unit increased. Dominant cows were less likely (~50%; p < 0.001) to drink water than intermediate and subordinate cows. In general, the odds of a cow lying in the sunny areas were 62% lower than in the shaded areas (p < 0.001). However, in winter cows were less likely (75%) to perform comfort behaviors (idling and rumination lying down) in shaded areas than in the sunny areas (p < 0.01). Furthermore, lying increased by 9% for each additional soil surface temperature unit. Dominant cows were more likely (~40%; p < 0.001) to lie down in the shaded areas than intermediate and subordinate cows. In conclusion, the cows’ location in the silvopastoral system was influenced by the black globe-humidity index and social hierarchy; in a situation of higher thermal challenge cows were more motivated to use shade, but dominant cows were more likely to use the shaded areas than other cows.