She removes her mares from the stallion so he's alone with an outside mare. She keeps the mare for a month. Most people like the option to pasture breed. It's more effective, with the goal to get her pregnant and get her home. She uses two breeding pens, measuring one or two acres in size and fenced with woven wire reinforced with electric wire.
Some owners are worried about a mare's spreading infection to the rest of the herd.
Breeders examine mares before turnout, and they report that stallions also check mares in the band. Some stallions seem to outsmart even veterinary science. Through scent, these horses decide to reject a mare which isn't in a physical condition to conceive. A stallion won't touch a mare if he senses something wrong. The nose knows.