Abstract
Simple SummaryThe 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.
Highlights
In many parts of the world, cattle may suffer from heat stress following exposure to solar radiation [1], which can negatively impact both the physiology [2] and the behaviour of cattle [3]
The maximum temperatures and the heat index were higher in summer compared to autumn (Table 1)
We did not evaluate the preference for each of the specific areas in the WITH SHADE treatment, our work suggests that motivation is associated with preference, given that, under the conditions of the present study, heifers showed some preference for the shaded areas, during the warm summer months
Summary
In many parts of the world, cattle may suffer from heat stress following exposure to solar radiation [1], which can negatively impact both the physiology [2] and the behaviour of cattle [3]. Little is known about the motivation expressed by cattle to access shade. Motivational tests for animals are used in research to investigate the importance of resources to animals [6]. The motivation to access shade can be experimentally tested to measure its importance to cattle. Operant conditioning, where animals are required to perform a particular behaviour to receive a reward [8], is a common experimental paradigm used to assess motivation [9,10]. The animals learn to associate the reward with the need to perform a specific behaviour; a measurable cost can be quantified following the performance of the behaviour, often referred to as the price paid [11]. The underlying assumption is that the more the animals pay to access the reward, the stronger the motivation [10]
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