Mary Allen
Too little exercise, slippery floors, concentrated feed, and happy growth are the undoing of many horses. This will damage joints.
Every year over 20,000 foals are born in Europe that develop osteochondrosis (OC). If they are lucky, this joint disease will not greatly affect their future performance. If they are unlucky, it means their end. “About ten percent of the horses I see are affected,” estimates Hansjakob Leuenberger, chief veterinarian at Tierklinik 24 in Staffelbach, Aargau. In Switzerland, around 150 foals fall ill with OC every year. This leads to changes in the bone-cartilage layer in the joint (see box).
In 1947, a Swedish veterinarian first described the problem. “But nobody talked about it until the 1960s. This was not because the disease could not have been diagnosed. It just didn’t come up,” says René van Weeren, equine veterinarian and researcher at the University of Utrecht in the Netherlands. He is an internationally renowned expert on osteochondrosis. “This disease is man-made,” he says. “We should change some things in the rearing of the horses.”
Osteochondrosis (OC)
In the embryo, the skeleton consists of cartilage that gradually ossifies. This ossification process is deficient in OC. Depending on the study, between 6 and 68 percent of horses are affected. Typical is a sudden joint swelling in the yearling (usually without lameness). OC can occur in almost any joint, but it is most common in the ankle. Both sides are often affected.
Diagnosis is by X-ray or ultrasound. How often OC is detected also depends on how many joints are examined – although even larger defects visible on the X-ray can disappear spontaneously by the age of about twelve months.
Why so many suddenly suffered from it – especially warm-blooded animals – has been researched for a long time. In a recent study, Dutch researchers observed foals on five farms. She was most interested in whether the animals slipped when standing up. Depending on the soil conditions, this did not happen at all on-farm number 1, but in farm number 3 it did so in over 30 percent of the cases. At twelve months, less than 10 percent of the foals on Farm 1 had osteochondrosis, among those on Farm 3 the figure was almost 15 percent. This can be a coincidence – or indicate circumstances that contribute to the OC.
“There are several factors underlying this disease,” says Leuenberger. One is the terrain. “If the foals gallop downhill on uneven, possibly rocky terrain and then stop suddenly at the fence, that puts a strain on the cartilage. Something like that favors micro-injuries.”
A too little exercise is similarly harmful. On-farm 3, the foals were only given a small paddock for one to two hours a day, and each had eight square meters of space in the stable. On courtyard 1, the animals could always move around in the pasture or in an area of 1250 square meters.
Complex Inheritance Patterns
The second important environmental factor is diet. “Easily digestible concentrated feed promotes the development of osteochondrosis,” says van Weeren. The carbohydrates in it cause the hormone insulin to rise sharply. This has a negative effect on cartilage maturation.
The horses also grow faster with high-energy feed. Large horses are particularly affected by the OC. Ponies and wild horses, whose height at the withers hardly ever exceeds 1.60 meters, are practically never affected. Both size and rapid growth, therefore, promote cartilage damage.
This poses problems, because “cheerful growth” is desirable inbreeding. And the inherited genes contribute significantly to this. Here the breeders are challenged. “A lot has happened in Switzerland in this regard,” says Leuenberger. “Horse breeders have recognized the problem. We see fewer foals with osteochondrosis today than we did 25 years ago.”
Depending on the breed, the OC is inherited to a greater or lesser extent. On average, the genes are responsible for almost a third of the disease, according to van Weeren, around two-thirds are due to environmental factors. He doesn’t think it’s a good idea to consistently exclude affected animals from breeding: “For many horses, the disease isn’t a big issue because it doesn’t lead to a loss in performance. Excluding them from breeding means losing a lot of valuable genetic potential.”
There will hardly ever be an OC genetic test. Because the affected genes are distributed on at least 24 of 33 chromosomes – too many to be able to eradicate them all by selection argues van Weeren and cites the breeding association of Dutch warmbloods as an example. Since 1984 no stallions with an OC in the hock have been licensed there, and since 1992 none with an OC in the knee either. “Nevertheless, the frequency of OCs did not decrease significantly until around mid-2015.”
Spontaneous Healing or Surgery
He would not generally advise against buying a horse with OC. “First of all, it depends very much on which joint is affected and how badly. Secondly, a lot of minor joint damage disappears with OC.” However, the “point of no return” is usually reached by around twelve months: joint defects that have not repaired themselves by then remain.
Spontaneous healing is one reason why very young animals or those with only minor joint damage are treated with anti-inflammatory painkillers and rest. In the case of larger joint defects, only an arthroscopic procedure can help. The chance that the horse can then be used in sport is usually between 60 and 85 percent.
After a successful operation, the horse is no longer legally considered “defective,” says Leuenberger. “The perfect horse that doesn’t have anything doesn’t exist anyway.”