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  Discussion on Functional adaptation of articular cartilage
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Moderator:
DrO

Posted on Monday, May 2, 2005 - 11:00 am:

There are few discussions on Horseadvice.com that get the attention as those involving when to start training horses. Since the published works of the numerous lesions found in horses vertebrae and the late closing times of the growth plates of the vertebrae the discussion intensified. However there have been studies to show that racing TB's started early have fewer injuries. Here is another report that supports the idea that early controlled work may strengthen a horse's ability to stay sound. Please note I have seen more than a few 2 year olds with advanced osteoarthritis who were started frequent working as a yearling.
DrO

Equine Vet J. 2005 Mar;37(2):148-54.
Functional adaptation of articular cartilage from birth to maturity under the influence of loading: a biomechanical analysis.

Brommer H, Brama PA, Laasanen MS, Helminen HJ, van Weeren PR, Jurvelin JS.

Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

REASONS FOR PERFORMING STUDY: The concept of functional adapatation of articular cartilage during maturation has emerged from earlier biochemical research. However, articular cartilage has principally a biomechanical function governed by joint loading. OBJECTIVES: To verify whether the concept of functional adaptation can be confirmed by direct measurement of biomechanical properties of cartilage. HYPOTHESIS: Fetuses have homogeneous (i.e. site-independent) cartilage with regard to biomechanical properties. During growth and development to maturity, the biomechanical characteristics adapt according to functional (loading) demands, leading to distinct, site-dependent biomechanical heterogeneity of articular cartilage. METHODS: Osteochondral plugs were drilled out of the surface at 2 differently loaded sites (Site 1: intermittent impact-loading during locomotion, Site 2: low-level constant loading during weightbearing) of the proximal articular cartilage surface of the proximal phalanx in the forelimb from stillborn foals (n = 8), horses of age 5 (n = 9) and 18 months (n = 9) and mature horses (n = 13). Cartilage thickness was measured using ultrasonic, optical and needle-probe techniques. The osteochondral samples were biomechanically tested in indentation geometry. Young's modulus at equilibrium, dynamic modulus at 1 Hz and the ratios of these moduli values between Sites 1 and 2 were calculated. Age and site effects were evaluated statistically using ANOVA tests. The level of significance was set at P<0.05. RESULTS: Fetal cartilage was significantly thicker compared to the other ages with no further age-dependent differences in cartilage thickness from age 5 months onwards. Young's modulus stayed constant at Site 1, whereas at Site 2 there was a gradual, statistically significant increase in modulus during maturation. Values of dynamic modulus at both Sites 1 and 2 were significantly higher in the fetus and decreased after birth. Values for both moduli were significantly different between Sites 1 and 2 from age 18 months onwards. The ratio of values between Sites 1 and 2 for Young's modulus and dynamic modulus showed a gradual decrease from approximately 1.0 at birth to 0.5-0.6 in the mature horse. At age 18 months, all values were comparable to those in the mature horse. CONCLUSIONS: In line with the concept of functional adaptation, the neonate is born with biomechanically 'blank' or homogeneous cartilage. Functional adaptation of biomechanical properties takes place early in life, resulting in cartilage with a distinct heterogeneity in functional characteristics. At age 18 months, functional adaptation, as assessed by the biomechanical characteristics, has progressed to a level comparable to the mature horse and, after this age, no major adaptations seem to occur. POTENTIAL RELEVANCE: Throughout life, different areas of articular cartilage are subjected to different types of loading. Differences in loading can adequately be met only when the tissue is biomechanically adapted to withstand these different loading conditions without injury. This process of functional adaptation starts immediately after birth and is completed well before maturity. This makes the factor of loading at a young age a crucial variable, and emphasises the necessity to optimise joint loading during early life in order to create an optimal biomechanical quality of articular cartilage, which may well turn out to be the best prevention for joint injury later in life.
Member:
Lhenning

Posted on Tuesday, May 3, 2005 - 1:10 pm:

DrO,

Can you summarize this for those of us that are scientifically challenged?

Thanks,
Linda
Moderator:
DrO

Posted on Tuesday, May 3, 2005 - 6:34 pm:

Early controlled work may strengthen a horse's ability to stay sound. However we still do not know how early and how much work, Linda. Hopefully more work will be forth coming on this topic.
DrO
Member:
Christos

Posted on Wednesday, May 4, 2005 - 9:33 am:

DrO, I always had the -perhaps stupid- feeling that it is exrcise from 6-8 to 18-24 months old that does all the damage.
Young foals seem to handle their weight and movement pretty well, then they lose it until 2yo or older.
Can it be that exercising a 2mo is safer than exercising a yearling ?
At what age would damage be apparent if a foal is regularly exercised until weaning ?
Member:
Christos

Posted on Wednesday, May 4, 2005 - 9:40 am:

Does the thought that a foal who rarely lies down (except at night) stands "sounder" on its legs make any sense to you ? (not a nervous or hungry foal)
Moderator:
DrO

Posted on Thursday, May 5, 2005 - 6:32 am:

With no specific long term work on large numbers of foals, I would not begin exercising foals. However I would give them all the opportunity I could to exercise themselves. Also I would see if I could find ways to develop an environment that stimulated exercise that simulates the horses intended use. The answer to "when would damage be apparent" depends entirely on the amount of damage. It could be immediate with swelling and lameness or it could be years if there it has mildly damaged the articular cartilage.

Interesting thought about the standing foal perhaps having better cartilage but there could be another reason: a foal that lays down a lot might be suspect for other lameness or cardiovascular issues.
DrO
Member:
Christos

Posted on Thursday, May 5, 2005 - 8:29 am:

Thanks, Doctor.
I am asking this, as you probably understood, because I did exercise my little one a lot as a foal. He never looked the least bit tired or reluctant, during the exercise or in the next days. I've taken him to the beach 4 times, at 2, 3, 4 and 5mo. 20km round trip, 1 hour trot to go, 1 hour break, 1 hour trot back. Both at the beach and back at home he was jumping around and playing sprints as if nothing happened.
He has never lied down during the day, he doesn't even catch a nap standing.
I knocked all exercise off at 6mo as he got unbalanced and clumsy. He is 13mo now, as sound as they come and still hopping around all day long. There's no sentivity I can see in his joints, meaning no hesitation or shortening of stride on hard surfaces.
I guess we'll have to wait a few years to see what the results of all this will be. He'll surely have some endurance use, so in some 6-7 years we'll definitely see how it worked out.

(I can almost see you shaking your head, but someone has to do these stupidities, no? )

Thanks again for your comments,
Christos
Moderator:
DrO

Posted on Thursday, May 5, 2005 - 10:35 am:

Not at all Christos, you may have actually strengthened rather than weakened these foals, we don't know.

The earliest and mildest sign of a problem would be swelling in the front of the knees or distension of the tibio tarsal (hock) or fetlock (volar pouches) jt capsules. If these look very clean I don't think there is much to worry about. Right now, stories like these are probably our best indication of what foals can tolerate without increasing problems.

I can think of two halter QH's that were lunged extensively as long yearlings from the history I could gather: 20 minutes plus, 5 days a week for months. Both developed remarkable arthritis in the knees by the time they were 2 years old which has always made an impression on me. It makes me cautious about forced exercise but with just 2 horses it is hard to draw firm conclusions and I am a firm believer that our small circles are hell on a horse's muscoskeletal system.

Anyone out there with other stories of working immature horses with either good or bad outcomes? Don't be shy and we will not tolerate any negative critisism, this is an important topic where we have little in the way of facts.
DrO
Member:
Christos

Posted on Thursday, May 5, 2005 - 12:00 pm:

Thanks again for your comments, DrO.
I have to stress that none of his exercise was forced by any means. One can think that he was psycologically forced to follow his mother or other horses, but this is not the case.
What is interesting is that his mother was stopping every 3-4km or so to check him up. Just a quick sniff over his face, like checking his breathing or temperature, and off she went again all by herself.
He was following free, not ponied, and most of the time he was breezing ahead of the group.
He has never been lunged and will not be until he matures to his final balance (I believe lungeing 20min+ five days a week for months would cripple any horse, even endurance champions).
Besides these 4 rides to the beach he was allowed to join riding lessons two-three times a week for an hour, never two consecutive days. He did spend the most part, if not the full hour, galloping, bucking and generally annoying everybody.
His legs and joints look and feel perfectly clean (as far as I can look and feel).
He is now turned out full time to reach maturity and he only exercises as much as he feels like it (he does nip and annoy every other animal to provoke a chase but nobody seems to be interested).

All the best,
Christos

PS: If you are to buy a TB off the track, buy the one that has been daily ponied, walked or ridden as a long yearling instead of lunged at a trot. It makes a significant difference. Breezing on the racetrack with a balanced jockey on board does not destroy long yearlings, trotting in circles does.
Member:
Lhenning

Posted on Friday, May 6, 2005 - 11:57 am:

Dr. O,
When I bought my quarterhorse he was 21 months old. I was totally inexperienced and knew nothing of age issues and riding. He was unbroke and I told the seller I would not buy him if I couldn't ride him, so she began breaking him to ride at that age. (She never said anything to me about this being bad for him, which still bothers me to this day.) He was ridden from age 21 - 23 months, twice a week for 20 - 30 minutes along with round-pen training three times a week for 20 minutes. All his riders have been between 130 and 160 pounds. In the next three months, the riding increased to twice a week for 30 - 40 minutes and the round-pen work stayed the same. Now he is a four-year-old and being ridden three times a week for 60 - 90 minutes. At this point, he has never had any joint problems or signs of arthritis, nor any swelling, but I always wonder what the future may hold. He is not going to be used for any type of competitive work, so it is not an issue of money, but I am concerned for his own well-being and comfort.

If I understand the article, it is saying that light work may actually be beneficial? They don't discuss being ridden though, so I am still uncertain if that my have caused him harm.

Thanks for your insight.

Linda
Moderator:
DrO

Posted on Friday, Aug 5, 2005 - 10:09 am:

Last month (see first discussion above) we were surprised to learn that equine cartilage matures very early in the growing horse. While maturing the cartilage adapts to stress, suggesting that early exercise (play or actual work) that mimics the intended endeavor of the adult horse makes sense but that we still don't know how much is optimal and more importantly, how much is too much.

This month we provide another side of this coin where we learn that the substructure to the cartilage of the joint does not finish maturing until 4 years of age. Though the soft components to these area matured early along with the cartilage, mineralization is not completed until 4 years, supporting the idea that these areas do not reach there maximal strength till then and that full training should not be started before then. I know everyone is going to ask so what do we do with our 2 and 3 year olds and I know that race horses started early actually seem to hold up better, at least in the short run, but these are all questions that we do not have definitive answers to yet and the best answers we have are learned by the results of traditional practices.
DrO

Study of cartilage and bone layers of the bearing surface of the equine metacarpophalangeal joint relative to different timescales of maturation.

van der Harst MR, van de Lest CH, Degroot J, Kiers GH, Brama PA, van Weeren PR.

Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.

REASONS FOR PERFORMING STUDY: A detailed and comprehensive insight into the normal maturation process of the different tissues that make up functional units of the locomotor system such as joints is necessary to understand the influence of early training on musculoskeletal tissues. OBJECTIVES: To study simultaneously the maturation process in the entire composite structure that makes up the bearing surface of a joint (cartilage, subchondral and trabecular bone) in terms of biochemical changes in the tissues of juvenile horses at 2 differently loaded sites of the metacarpophalangeal joint, compared to a group of mature horses. HYPOTHESIS: In all the structures described above developmental changes may follow a different timescale. METHODS: Age-related changes in biochemical characteristics of the collagen part of the extracellular matrix (hyDrOxylysine, hyDrOxyproline, hyDrOxypyridinum crosslinks) of articular cartilage and of the underlying subchondral and trabecular bone were determined in a group of juvenile horses (n = 13) (Group 1, age 6 months-4 years) and compared to a group of mature horses (n = 30) (Group 2, >4 years). In both bony layers, bone mineral density, ash content and levels of individual minerals were determined. RESULTS: In cartilage, subchondral bone and trabecular bone, virtually all collagen parameters in juvenile horses were already at a similar (stable) level as in mature horses. In both bony layers, bone mineral density, ash- and calcium content were also stable in the mature horses, but continued to increase in the juvenile group. For magnesium there was a decrease in the juvenile animals, followed by a steady state in the mature horses. CONCLUSIONS: In horses age 6 months-4 years, the collagen network of all 3 layers within the joint has already attained a mature biochemical composition, but the mineral composition of both subchondral and trabecular bone continues to develop until approximately age 4 years. POTENTIAL RELEVANCE: The disparity in maturation of the various extracellular matrix components of a joint can be assumed to have consequences for the capacity to sustain load and should hence be taken into account when training or racing young animals.
Member:
Imogen

Posted on Saturday, Aug 6, 2005 - 2:45 am:

Maybe this isn't directly relevant but... a few months ago there was a discussion here that Christos participated in about the Dutch long-term study of training showjumpers early (loose jumping etc.) and the final conclusion as I remember being it does work, and doesn't seem to affect soundness but it unfortunately appears to demotivate the horses over a period of years, particularly bad news for showjumpers who have much longer careers than other equines...

I heard on RTE (Irish state broadcaster)'s Farming programme recently a very interesting Swedish professor (sorry it was early morning, I didn't write down his name/university) talking about a long-term project he is doing where instead of formal schooling, they keep mares and foals on a large farm where the horses decide themselves when to move to the next field but the researchers have set up small jumps, banks or other obstacles such that the mare teaches the foal to get over the obstacles get to the next grazing area.

He said the mares do teach the foals to jump, and the horses themselves decide how often to go over the obstacles. There are no published results yet but like the Dutch study, they have another controlled group getting standard care without the natural jumps and it is to be a long term project (which he said is possible due to the removal of cattle subsidies making land available at a cost which allowed funding of the project to be feasible).

I think this will be particularly interesting for European continental breeders who often have such restricted grazing that young horses hardly know what grass is (but also have the best jumpers competing internationally). Natural grazing and the requirement to navigate natural obstacles are often put forward as the reason why Irish horses are pretty smart about this kind of thing, and I can think of quite a few horse farms where this type of thing is practiced by default (because the field boundary ditches haven't been maintained), so it will be interesting to find out if it has a statistically significant effect and whether there is any consequence for soundness.

All the best

Imogen
Member:
Hwood

Posted on Saturday, Aug 6, 2005 - 3:13 am:

VERY interesting, Imogen. Thanks for sharing.
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