In France, horse rearing is often associated with other farming activities such as beef or dairy productions that prevail in grassland areas. To analyse the role of horses on the sustainability of farming systems, we surveyed one hundred farms in four major areas of horse breeding, chosen in regard to their production system representative of regional agricultural systems. The regions differed in their agro-climatic context, associated with a type of horse production: saddle horses in oceanic and continental lowlands, and draught horses in two upland regions in Central and Eastern France. Farmers were questioned about the role of their equine production in the economic, environmental and social functioning of their farming system. Results showed that horse numbers ranged from less than 10 to 100% of the total livestock (expressed in livestock units). In upland areas, draught horses were appreciated for their use of grasslands along with or after cattle. These hardy horses needed little labour, but the low income from this production limited its development. In lowlands, farmers raised saddle horses either alone or with dairy or beef cattle. In farms specialized in horses, breeders developed allied services such as taking horses at livery. In mixed herds, farmers spent comparatively more time on saddle horses than on cattle, whether beef or dairy. The impact of saddle horses on gross production depended on numbers and age for sale. In conclusion, horse rearing presented a low profitability, especially for draught horses, or an unpredictable profitability, especially for saddle horses. However, whatever the types of animal production, horse grazing improved the maintenance of grassland areas, and farmers raised horses, which attracted volunteer labour, because they enjoyed taking care of them.