Growing Up Equine: A Guide to Horse Maturation

In the comments on my post on the Wise Elders of horsedom, a commenter asked about the maturation rate of horses. I could swear I did an article about that, but it seems I’ve mostly tossed bits and pieces into articles on other, related subjects. Definitely it’s time to remedy the omission.

I have talked about breeding, gestation, and foaling, in posts which you will find here and here. Now let’s look at your young horse on the hoof. A newborn baby, up to about six months old, is referred to as a foal. The female version is a filly and the male is a colt—appellations that will carry through for two or three years depending on the breed and discipline. Hence you hear about “colts” and occasional “fillies” running in the Kentucky Derby; they’re in their third year, and are not considered fully mature, though they’re doing a full-time job as racehorses.

From about six months of age until the first birthday, the foal becomes a weanling: weaned from its mama, but still very much a baby. Come the first birthday, they’re called a yearling. Then as the birthdays tick away, a two-year-old and a three-year-old. Come age four, they’re generally regarded as an adult, though their musculoskeletal system will not actually be fully mature until around age five or six, or even later in some breeds and individuals—sometimes as late as eight years old.

During this time of maturation, the horse will fill out and may add some height, again a very individual process. I’ve seen horses reach their adult height by age four, and I’ve seen others add inches until ages eight or, once, up to about age ten. That was a very late bloomer.

It pays to know the horse’s breeding and family lines. There’s always one who goes their own way—the brother who soars to 16.2 hands (at four inches per hand, measured from the ground to the withers), while his 14.3-hand parents produce siblings who grow at the usual rate and quantity of their line—but for general purposes, if you’ve seen the parents and the siblings, you can fairly well estimate how big your foal will get. There’s also the size of the foal themself; if they come out big, and keep on growing in proportion to their birth size, they’re probably going to be a sizey adult.

Big does not equal mature. That’s important to remember. In fact, the bigger the foal, the higher their chances of joint and bone problems, especially if they grow rapidly. It’s if anything more important not to start the big kid too early or work them too hard, no matter the temptation. Better to wait and give them time to develop.

Musculoskeletal maturity and sexual maturity are not congruent. A filly may have her first heat in her yearling year, and may start cycling even before that. A colt meanwhile can be fertile at a remarkably young age. Putting your colts out with your fillies might be all right when they’re first weaned, but by nine months or so, unless you want to risk an oops, it’s a good idea to run them in separate herds.

If your colt is not going to be a breeding stallion—and the majority are not—he’s generally gelded as a weanling, though some breeders may wait a year or more to see how he grows, and to allow him to develop greater muscularity. Supposedly a gelding may grow a little taller than a stallion, but he’ll have a lighter build and he won’t grow the cresty neck and prominent jaws of a stallion.

Fillies are not spayed except in very rare cases, usually for medical reasons. Gelding is a simple outpatient surgery. Spaying a mare is major surgery and carries real dangers to the mare’s life. If there are reasons to suppress or control her cycles, there are effective medications that will do the job.

Carrying a foal demands a lot of a mare’s body, and for the most part it’s best to wait until she’s mostly mature before breeding her. In most breeds, that’s age three and up; some of the later-maturing breeds recommend waiting until she’s four or five. Colts don’t have the same strictures, but there are behavioral reasons to wait until he’s at least two and preferably three or older, when he’s had more training, some of it in his adult job—ridden or driven. Training a colt helps focus his mind and dispose him to be a little more willing to listen to the handler when he’s being bred.

As for when to start work, again that depends on the maturity of the horse. Racing Thoroughbreds tend to get a lot of their adult height as yearlings. In the US, they’re started under saddle around eighteen months, to be ready to race as two-year-olds. Other disciplines, including some show breeds and types, also start young. Dressage for example does not allow competition before thirty-six months, though that means training may start a year or more before that.

My personal inclination is to wait and go slow. I work with a late-maturing breed to begin with, but it’s also quite long-lived and will stay sound well up into the twenties if started and brought along gradually. The rule there is to wait until at least the four-year-old year to begin training under saddle, though with plenty of handling from birth, and not to push the horse into full work until at least age six.

Contrast that with racehorses who are retired to stud or the broodmare herd as three-year-olds, and show horses perceived as “aged” at five. The later bloomers aren’t bred until age five or older, and the recommendation is to get them going under saddle before breeding—again, with the stallions, to help with handling during the process.

A lot of this is financially motivated. It costs a boatload of money to keep a horse. The earlier they can be pushed to win the prizes that make them a hot item for breeding (with appropriately stratospheric stud fees) and put high price tags on their offspring, the more cost-effective they are.

But at home in the pasture, where the horse mostly would rather be, the rate of maturation continues at pretty much the same rate regardless of breed or quality. Too much push too soon will break down the horse at a young age (hence the “aged” five-year-old), but presuming they’ve been handled with at least some care for their longterm well-being, the horse has a pretty good chance of cruising along into their early teens as a sound and fairly young horse.

By the teens they’re starting to slow down a little bit. Mid to late teens are getting up in middle age, though if they’ve been managed well, they’re still quite sound to work. A horse headed toward twenty is heading toward old age, with a life expectancy around twenty-four years, though some horses cruise past thirty and even, in some cases, into the forties.

How long can you ride or work them? It’s highly individual. One horse may be done at seventeen. Another may still be doing advanced dressage at thirty-two, though he might have had to taper off on his piaffe.

The original commenter asked if horses have an accelerated rate of ageing versus a slower beginning, as compared to humans. My answer to that is, No, not really. If the horse is physically mature around age six, and has a life expectancy of about twenty-four years, that’s roughly a quarter to a third of the human rate and span. I actually found a chart that purports to estimate the approximate age of a horse in human years, for what that’s worth. It’s not terribly far off, taking all in all.

From the perspective of a horse owner who also has cats and dogs, horses are blessedly long-lived. At an age when a dog is close to the end of their lifespan, the horse is just settling into middle age. The horse I bought as a four-year-old was with me for twenty-six years, and one of my friends had thirty-seven years with her loved mare, from birth to death. It’s not long enough, it never is, but we appreciate those extra years.

Judith Tarr’s first novel, The Isle of Glass, appeared in 1985. Since then she’s written novels and shorter works of historical fiction and historical fantasy and epic fantasy and space opera and contemporary fantasy, many of which have been reborn as ebooks. She has written a primer for writers: Writing Horses: The Fine Art of Getting It Right. She has won the Crawford Award, and been a finalist for the World Fantasy Award and the Locus Award. She lives in Arizona with an assortment of cats, a blue-eyed dog, and a herd of Lipizzan horses.


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