Breeding boars are usually supplied by a breeding company who analyses the feed conversion, growth rate and carcass quality of siblings. They are usually selected at six to eight months old, and will start with four to six sows. As libido and fertility increases, the ratio increases to about one boar per 25 sows. Young boars are often group housed in group pens, possibly with straw, but incarcerated individually when older. Boars lead a life of utter frustration and boredom, these large, fiercely intelligent animals (the size of a Shetland pony) are left in (often filthy) pens with absolutely nothing to do.