Young Horses, vs Physical Maturity

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Tue Nov 20, 2018 3:22 am

Wasn't sure where to put this but thought it would be interesting to share since every now and then discussion about running babies comes up.

People can certainly debate and argue over different training techniques and styles but we can not argue the science.

"Owners and trainers need to realize there's a definite, easy-to-remember schedule of fusion - and then make their decision as to when to ride the horse based on that rather than on the external appearance of the horse.
For there are some breeds of horse - the Quarter Horse is the premier among these - which have been bred in such a manner as to LOOK mature long before they actually ARE mature. This puts these horses in jeopardy from people who are either ignorant of the closure schedule, or more interested in their own schedule (for futurities or other competitions) than they are in the welfare of the animal.

The process of fusion goes from the bottom up. In other words, the
lower down toward the hoofs you look, the earlier the growth plates will have fused; and the higher up toward the animal's back you look, the later. The growth plate at the top of the coffin bone (the most distal bone of the limb) is fused at birth. What this means is that the coffin bones get no TALLER after birth (they get much larger around, though, by another mechanism). That's the first one. In order after that:

2. Short pastern - top & bottom between birth and 6 mos.
3. Long pastern - top & bottom between 6 mos. And 1 yr.
4. Cannon bone - top & bottom between 8 mos. And 1.5 yrs.
5. Small bones of knee - top & bottom on each, between 1.5 and 2.5 yrs.
6. Bottom of radius-ulna - between 2 and 2.5 yrs.
7. Weight-bearing portion of glenoid notch at top of radius - between 2.5 and 3 yrs.
8. Humerus - top & bottom, between 3 and 3.5 yrs.
9. Scapula - glenoid or bottom (weight-bearing) portion - between 3.5 and 4 yrs.
10. Hindlimb - lower portions same as forelimb
11. Hock - this joint is "late" for as low down as it is; growth plates on the tibial & fibular tarsals don't fuse until the animal is four (so
the hocks are a known "weak point" - even the 18th-century literature warns against driving young horses in plow or other deep or sticky footing, or jumping them up into a heavy load, for danger of spraining their hocks)
12. Tibia - top & bottom, between 2.5 and 3 yrs.
13. Femur - bottom, between 3 and 3.5 yrs.; neck, between 3.5 and 4 yrs.; major and 3rd trochanters, between 3 and 3.5 yrs.
14. Pelvis - growth plates on the points of hip, peak of croup (tubera sacrale), and points of buttock (tuber ischii), between 3 and 4 yrs.

and what do you think is last? The vertebral column, of course. A
normal horse has 32 vertebrae between the back of the skull and the root of the dock, and there are several growth plates on each one, the most important of which is the one capping the centrum.

These do not fuse until the horse is at least 5 1/2 years old (and this figure applies to a small-sized, scrubby, range-raised mare. The taller your horse and the longer its neck, the later full fusion will occur. And for a male - is this a surprise? -- You add six months. So, for example, a 17-hand TB or Saddlebred or WB gelding may not be fully mature until his 8th year - something that
owners of such individuals have often told me that they "suspected" ).

The lateness of vertebral "closure" is most significant for two
One: in no limb are there 32 growth plates!
Two: The growth plates in the limbs are (more or less) oriented perpendicular to the stress of the load passing through them, while those of the vertebral chain are oriented parallel to weight placed upon the horse's back.

Bottom line: you can sprain a horse's back (i.e., displace the
vertebral growth plates) a lot more easily than you can sprain those located in the limbs.

And here's another little fact: within the chain of vertebrae, the
last to fully "close" are those at the base of the animal's neck
(that's why the long-necked individual may go past 6 yrs. to achieve
full maturity). So you also have to be careful - very careful - not to
yank the neck around on your young horse, or get him in any situation where he strains his neck."

Dr. Deb Bennett

ABOUT DR. DEB: Deb Bennett, Ph.D., is a 1984 graduate of the University of Kansas, and until 1992 was with the Smithsonian Institution. She is known as an authority on the classification, evolution, anatomy, and biomechanics of fossil and living horses. Her research interests include the history of domestication and world bloodlines and breeds. She teaches unique anatomy short-courses and horsemanship clinics designed to be enjoyable to riders of all breeds and disciplines, and all levels of skill.

Internationally known for her scientific approach to conformation analysis, "Dr. Deb" has made a career out of conveying a kind of "X-ray vision" for bone structure to breeders and buyers. Her background in biomechanics helps her clearly explain how conformation relates to performance ability. Dr. Deb's clinics often feature real bones and interesting biomechanical models.
Source: ... __tn__=C-R
A filly named Ruffian...

Eine Stute namens Danedream...

Une pouliche se nommant Trêve...

Kincsem nevű kanca...

And a Queen named Beholder
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Tue Nov 20, 2018 9:31 am

Treve, thank you for that post. I found it quite educational.
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Sparrow Castle
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Tue Nov 20, 2018 4:42 pm

It is interesting. I think we knew that horses aren't fully mature until they're about 5 years old, but I'd never seen the schedule of bone fusion. I'm not sure if this means the horse shouldn't bear weight until all bones are fused though. Other studies show benefits of weight bearing early in the development process. I think most good trainers are very considerate of limb growth plates when they decide a horse's training schedule. Not sure that applies to the vertebral bones though. Maybe trainers who are somewhat large people shouldn't be galloping their own babies?
lurkey mclurker
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Tue Nov 20, 2018 7:41 pm

Wow. I think that has a lot of implications for dressage, actually, with the demands that (true) collection & self-carriage put on the neck/back... thanks for posting that!
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Thu Nov 22, 2018 5:35 am

Overall the article has some really good information. I do have a slight hiccup though when she calls displacing a growth plate a "sprain". Displacing a growth plate would be a bone fracture (Salter Harris type 1 to be specific), and is exceedingly rare (I've never seen a displaced epiphysis). So I don't really understand the comment that young horses can "sprain a back" more easily than "spraining" a plate in a leg. Other types of growth plate fractures can happen as well, such as crushing (Salter harris type 5) and through/condylar fractures, and those would happen in a leg much more easily than a back. She also seems to be implying that if a person were to yank on a horse's neck too much, they could fracture their vertebrae (or 'sprain' as she puts it). Now of course there's lots of reasons to not yank on a horse's head, but most people don't have nearly enough strength to break a horse's neck.
I think she means well, but I've always tried to stay neutral on the subject of working young horses because there are also multiple studies that show fewer catastrophic injuries in horses that are started younger. I don't know what the right answer is, and its probably not a black and white situation. (I will say that I'm not a fan of 2yo in training sales early in the year, some of those horses are pushed way too fast before they've been prepped for it).
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