Leeftijd bij Inrijden

This article was originally published in English by the author on the Equine Independent website in June 2013
There must be something in the air at the moment; I was recently expounding the virtues of delaying a horse’s training under the saddle only to come across an article last week on The Horse website talking about (race)horse performance at 2, 3 and 5 years related to lesions.
The cause was at that moment of little interest, the age of the horses was. Should we be riding at such immature ages?
Despite being worlds apart, the racehorse industry and the home-hack do have one main thing in common, the wish to turn their beautiful horse into a beautiful rideable horse as soon as possible. After all, most of us don’t just want to look at our horse…
There is plenty of motivation to start early too. In dressage, there is a minimum age at which a horse may compete; according to FEI regulations for international dressage competition, it is six years but for many national events, the rules are different with the minimum age being as low as three. And when one considers horse-racing, the ages are even lower – the racing of two-year-olds is quite commonplace which requires them to be saddled up for the first time when they are not much older than 1½.
For the professional trainer and owner, it is all a question of money. Often the horse is – or can become – quite valuable. Keeping a horse costs money (ironically, for the owners of such horses, it is often just a fraction of their earnings) and the natural desire is to see the horse earn its keep as soon as possible. And eventually, a racehorse can be put out to stud and earn yet more that way – these days not even needing to attain a respectable age with the ability to freeze sperm – but the health of the horse is never the greatest consideration.
So what about the mere mortals of this world? Most horse owners will agree that a horse should not be ridden until it is about 4 years old. A respectable age, one could say; the horse is obviously no longer a foal and is more likely to grow outwards than upwards. However, the growth plates, correctly known as centres of ossification or simply ossification centres are still a long way off being closed. The last ossification centres will close somewhere between 5½ and eight years old – and it is specifically these centres that are found in the back of the horse – all 32 of them!

Most ossification centres lie across the weight bearing plane – think of knees, ankles, shoulders etc. – and are less affected by the carriage of weight. But those in the back lie parallel to the weight bearing plane whereby the back is easily stretched and thus can suffer under the weight of the rider.
To clarify, this is the order and the approximate age at which the ossification centres close up:
skeleton of the horse

  1. Before birth:
    Metacarpus – proximal epiphysis†
    2nd Phalanx – distal epiphysis
    1st Phalanx – distal epiphysis
  2. Near birth
    3rd Phalanx (coffin bone)
  3. By three months
    Fibula – distal epiphysis
  4. 9 – 12 months
    2nd Phalanx – proximal epiphysis
  5. 12 months
    Scapula – bicipital tuberosity‡
  6. 13 – 15 months
    1st Phalanx – proximal epiphysis
  7. 15 – 18 months
    Humerus – distal epiphysis
    Radius – proximal epiphysis
    Metacarpus – distal epiphysis
  8. 16 – 20 months
    Metatarsal – distal epiphysis
  9. Before 2 years
    Ulna – distal epiphysis (two epiphyseal plates)
  10. 18 – 24 months
    Pelvis – hip socket components
  11. 20 – 24 months
    Tibia – distal epiphysis
  12. 2 – 3 years(?) variable
    Fibula – proximal epiphysis
  13. 3 years
    Scapula – tuber spinae‡
    Fibular tarsal – tuber calcis‡
  14. 3 – 3½ years
    Humerus – proximal epiphysis
    Femur – distal and proximal (two epiphyseal plates) epiphysis
    Tibia – proximal epiphysis
  15. 3½ years
    Radius – proximal epiphysis
    Ulna – olecranon‡
  16.  2 – 4 years
    Femur – 3rd trochanter‡
  17. 3 – 5 years
    Vertebrae* – accessory process and anterior physis
  18. 4 – 5 years
    Vertebrae* – Dorsal process, tip
  19. 4½ – 5 years
    Pelvis – ossification is complete
  20. More than 5 years
    Vertebrae* – posterior physis

* the larger the horse and the longer the neck, the later ossification of the vertebrae; for stallions, add another six months: this means a “warmblood” horse of about 17hh will not be fully grown until 8 years old.
† the end part of long bones is known as the epiphysis.
‡ these ossification centres are found in the larger protrusions along a bone’s length and are usually an attachment point for muscle, for example.
Of course, all this does not mean that we cannot do anything with our horses until they are eight, but it should certainly set us thinking about our training schemes.
For the professional horseworld, time is loss – except the economics are not taken into account. Maybe not so interesting for the racehorse owner – his horse is often little more than a money factory – but certainly for the livery and riding school owners. In much of Europe, the average age of a riding school horse is horrifically low and the general life-expectancy shows no correlation with what a horse should (healthily) be able to reach. Based upon the size of the animal and the size and rate of its heart etc., the horse has a potential life-expectancy of 50 years. Realistically a little lower at around 40 to 43 years. But a horrific number of horses has already been written off by the age of 20 – imagine writing off people when they get to 38 or 40…
Take a look at the table below – and decide for yourself which of the two columns fits your way of thinking best:

Begin training 3 years 7 years
Full potential 7 years 10 years
End “useful” life 18 years 35 years
Total work period 15 years? 25 years

Just by delaying the moment we start to ride by just 3 years, we can win 10 years in “useful” life. It makes you think…
 
◊ This document modified January 2016 to reflect the changes in Dr Bennett’s presentation and give clearer details of the ossification timeline.
Growth plate information: Timing and rate of skeletal maturation in horses, Dr Deb Bennett, 2008, from her original study published 2001
“Useful Life” table: based on observations by Pierre Enoff, bio-mechanical engineer
Original article by this author published in Dutch: http://sabots-libres.eu/site/engagement/2013/06/08/leeftijd-bij-inrijden/
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