Generally this is called multi-species grazing, or when more than one species of animal are used to graze a pasture; however, there is no term to describe horses and goats specifically. With horses, cattle will commonly graze one rotation behind horses in pastures. This helps more evenly graze the grasses in the pasture because cattle are not selective grazers like horses are and they are susceptible to different parasites. Sheep and goats are grazed with horses as companions or to help with woody plants and weeds in the pasture that horses will not eat.
