Dairy Heifer Motivation for Access to a Shaded Area

Simple Summary The aim of this study was to determine the motivation of pasture housed dairy heifers to access shade during southern Brazil's summer and autumn months, and if social rank affected shade use. Heifers valued shade and worked to access it, particularly on hot summer days. Heifers of higher social rank displaced other heifers more often and spent more time in the shaded areas, particularly in the area with trees plus a shade cloth, than the intermediate and subordinate heifers. We used an operant conditioning paradigm to test the motivation of non-pregnant dairy heifers to access shade during the summer and autumn months (January to June) in southern Brazil. Dairy heifers (n = 18) were trained to push a weighted gate to access either an experimental area containing both a shaded (simple tree shade and shade cloth) and unshaded area (WITH SHADE) or an experimental area with no shade (BARREN). The latency to push the weighted gate, and the maximum weight pushed by each heifer, were recorded in both the summer and the autumn. Temperature and humidity were recorded continuously for the duration of the study and were used to calculate the heat index. The maximum weight pushed to enter the WITH SHADE area was greater in summer than in autumn, and was inversely related to the latency to push the weighted gate. Heifers refused to work for access to the BARREN environment. As expected, both the maximum ambient temperatures and heat index were higher in summer than in autumn, and also higher in the non-shaded areas than under the shade in both seasons. Heifers of higher social rank displaced other heifers more often, and spent more time in the shaded areas, particularly in the area with trees plus a shade cloth, than the intermediate and subordinate heifers. We conclude that shade is an important and valued resource for heifers reared on pasture-based systems in sub-tropical environments, particularly during the hot summer months.

Automated summary

The study aimed to determine the motivation of pasture housed dairy heifers to access shade during summer and autumn in southern Brazil. It found that heifers valued shade, especially in hot summer days, and that social rank influenced shade use. Higher ranked heifers displaced others more often and spent more time in shaded areas, particularly those with trees and shade cloth.