As a general

rule these animals are sexually
capable when three years old, and they grow better for breeding
purposes until they reach twenty years. The stallion is sexually
capable up to the age of thirty-three years, and the mare up to forty,
so that, in point of fact, the animals are sexually capable all
their lives long; for the stallion, as a rule, lives for about
thirty-five years, and the mare for a little over forty; although,
by the way, a horse has known to live to the age of seventy-five.
The ass and the she-ass are sexually capable when thirty months old;
but, as a rule, they are not generatively mature until they are
three years old, or three years and a half. An instance has been known
of a she-ass bearing and bringing forth a foal when only a year old. A
cow has been known to calve when only a year old, and the calf grew as
big as might be expected, but no more. So much for the dates in time
at which these animals attain to generative capacity.