Newborn Foals: Big Babies, But Not the Biggest

An average-sized mare can produce a foal weighing about 100 pounds (45 kilograms), or about 10% of the mare’s own weight. This is neither the largest nor the smallest mammalian infant in comparison to the mother’s weight. At one end of the scale, female bats produce newborns weighing between 25% and 35% of their own body weight. At the other end, a female panda gives birth to a tiny four-ounce infant that is 0.1% of its mother’s weight.

While newborn Thoroughbred foals weigh about 10% of their mature weight, according to Kentucky Equine Research nutritionist Clarissa Brown-Douglas, Ph.D., draft horse mares produce foals that are about 7% of their mature weigh, while the foals of Shetland ponies may be as much as 13% of their mature weight. Pony foals tend to mature somewhat earlier than larger horses.

If all other factors are similar, larger foals tend to be produced by mares between the ages of 7 and 11, mares that have had one or more previous foals, and mares that are large themselves, Brown-Douglas said.

By six months of age, Thoroughbred foals have reached about 43% of their mature weight and 83% of their mature height. Foals born in the winter tend to be somewhat smaller than those born later in the spring, but the winter-born foals have a faster growth rate at three months old than the later-born foals and have completely caught up with growth rates of their latter-born peers by five months of age. At 12 months, foals will have achieved about 61% of their mature weight and 92% of their mature height.