| Summary: | Grazing behaviour of domestic horses on perennial ryegrass pastures and the effect of sward height On paddocks used for horse grazing, swards are often depleted by overgrazing and patches of bare ground appear due to resting and walking behaviour of the animals. In order to improve pasture production and animal management the knowledge of grazing and social behaviour is essential. The present study therefore investigated grazing behaviour of horses and their response to different sward heights and the influence of being a herd animal on individual behaviour. The experiments performed showed that horses perceive differences in sward height and that they increase bite dimensions, such as bite depth, volume, area and mass, as sward height increases. As bite depth slightly increased when the horses' whiskers around the rilUzzle were trimmed or shaved, it was shown that the whiskers play an important role in perceiving the distance of the muzzle to the vegetation. For reasons of animal welfare, it is suggested that the practice of whisker treatment is stopped. When presented with a choice between different sward heights, horses selected tall swards (> 8.2 cm) which supply the highest bite mass. However, when young grass leaves overtop the older ones on shorter areas, horses also graze these short patches, indicating that they switch between energy maximisation per bite and quality of food. When sward height declined, a slight increase in bite rate was observed. It is therefore suggested that when bite mass is constrained by sward height horses may increase bite rate in an attempt to maintain a constant gut fill. An increase in the total time grazing per day as a response to a decrease in sward height was not detected. Due to the observed impact of gregarious behaviour on grazing and resting behaviour of individual horses, it is suggested that horses should be kept in groups of at least two animals.
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