How do horses graze pastures and affect the diversity of grassland ecosystems?
Résumé
In an agricultural context promoting the development of sustainable grazing systems, horses – whose numbers are increasing in Europe – have a significant role to play. However, compared to ruminants, the lack of data on how horses exploit pastures makes it difficult to propose management recommendations, despite evidence that grass can cover their nutritional requirements and that pasture management can be used to manipulate vegetation dynamics. In this review, we report recent insights into factors that affect the voluntary intake and feeding choices of grazing horses, and we specify the consequences of their diet selection on biodiversity in grassland ecosystems. Horses have a greater intake capacity on roughages than ruminants, which enables them to effectively control competitive grasses and maintain open areas in pastures. When facing variations in resource availability and quality, horses are able to adjust their foraging behaviour (daily grazing time, instantaneous intake rate, feeding site selection) in order to meet their nutritional requirements. How horse characteristics can affect their voluntary intake and feeding choices needs to be specified. The specific mode of grazing employed by horses maintains short lawns within a matrix of tall grass areas, which is known to promote plant and animal diversity, at least in the short term. Horses make less use of forbs and legumes than ruminants, and further studies are needed to determine whether this behaviour could benefit flowering plants and pollinating insects.
