By: Brittany Bevis
During this time of year, horse breeders around the country anxiously await the arrival of the next generation. Months of planning and countless sleepless nights culminate in welcoming these new foals into the world.
Once it’s been determined that the new charges are healthy, all thoughts turn towards the future- envisioning what they could become two, five, ten years down the road. What disciplines will they excel in? What will their personalities be like? And, of course, how tall will they become?
While no method is 100% accurate when determining the future height of a foal, there are a few tricks of the trade that have been passed down through the ages. Of course, genetics, nutrition, injury, and other factors play a big part in determining where a horse will eventually fall on the stick.
Did you know that within the first few months, a foal will reach 75% of their mature height? By 18 months, a horse will have reached 90% of their mature height and weight. The exponential growth is so great during this period in a foal’s life that at any given time their hind end is often two to three inches taller than their withers. (theHorse, 2020)
A piece written by Christy Corp-Minamiji, DVM, Young Horse Development Part 2: Six Months to 1.5 Years, reflects on research conducted by TM Anderson and CW Mcllwraith, which showed that the growth of a horse is proportional, with long bone growth correlating to wither height. Because cannon and pastern bone measurements increased by only 5-7% from weaning until the age of three, it suggests that lower limb growth is complete by the yearling phase and that adult height can be predicted by a measurement of the cannon bone.
Stew Nelson, former staff writer at the Progressive Cattleman, spoke on this topic and conducted an experiment with his own horses to determine the accuracy of such a measurement. Taking a measurement in a straight line from the front of either leg, beginning at the hairline and extending upwards to the middle of the knee joint, is said to provide a measurement in inches that converts directly into hands on an adult horse. For example, a foal that measures 15 1/4 inches should translate into an adult horse that measures 15.1hh.
“This handy measurement, when broken down, is easily seen to be one-quarter of the horse’s mature height. Example: 14 ¼ inches multiplied by 4 = 57 inches, or 14.1hh; 15 ¾ inches multiplied by 4 = 63 inches or 15.3hh,” Nelson says.
So, he measured every mature horse in his barn, of all sexes. He compared the hairline to middle of knee measurement with their height, and he deemed it to be accurate on all his horses within the 14.1hh to 15.3hh range. Then, he did the same procedure on his foals and discovered it to be very close to what he anticipated they would mature to. After a few years of conducted his own tests, he determined the procedure to be very accurate to within 3/4 of an inch of a horse’s mature height.
Of course, there is likely to be human error with any sight measurement; therefore, it’s important to make sure a foal is standing square and evenly with pasterns flexed. Any shifting of weight will affect the measurement.
Kentucky Equine Research offers yet another method. This test involves measuring the distance from the ground to the foal’s elbow and then doubling that measurement to hint at the eventual distance from the ground to the withers. Still another, less scientific method, is to add two hands of height to a yearling’s height or one hand to a 2-year-old’s height.
Going even further, a piece written by Les Sellnow, Growing Up: Estimating Adult Horse Size, indicates that one of the best measurements of growth in a horse is weight. Since most horse owners don’t have a horse size scale handy, researcher G.W. Willoughby created a formula that uses a heartgirth measurement to determine weight.
“For mature males, the formula is this- body weight in pounds equals 0.14475 times heartgirth in inches. For mature females, it is 0.14341 times heartgirth in inches. For colts, which are five years of age and under, the multiplying factor is 0.1387 times heartgirth in inches + 0.400. For fillies, it should be 0.1382 times heartgirth in inches + 0.344.”
When estimating the size of a foal in adulthood, it’s important to review a few basic about genetics. Sellnow’s example of a breeder selecting a 14hh mare to breed to a 16hh stallion and then expecting a resulting 15hh foal is helpful.
“Genetics will dictate that we won’t get the in-between horse we have been seeking. The offspring would have inherited one or the other of the parent’s genes for growth. If it received the mare’s gene for growth, the offspring will likely wind up being short. If it inherited the stallion’s growth gene, it will likely be tall. This does not mean that the offspring will be the exact size of one of the parents. It means that one or the other of the genes-tall or short-will be expressed, and it is unlikely that the resultant foal would wind up midway between its parents in size.”
Regardless of the anticipated future height of your foal, it’s most important to have a happy and healthy animal. But, it is still fun to guess.