Page 57 - July 2020

EQUINE HEALTH
Developmental orthopedic disease (DOD) is a catch-all term that covers several abnormal skeletal developments due to improper bone growth in young growing horses.
months old, was always abnormal,” Schramme explains. “Now we realize that most young horses may develop some irregularity in the process of cartilage ossification, but these irregularities can self-repair. So, we don’t want to rush in and call this abnormal until the self-repair window of cartilage has come to a close, at about a year of age. The concept has changed from looking at OCD as a disease that is readily recognized radiographically, to think- ing that maybe it is part of the normal growing process--and it only becomes important if the self-repair hasn’t worked.”
CAUSES OF DOD
“All of these diseases occur more frequently in large, fast-growing young horses. The larger the young horse and the faster it is growing, the higher the chance it has one of these condi- tions, or even any combination of these,” says Schramme.
Breeders have inadvertently selected for these conditions, wanting youngsters big enough to compete in certain sports like racing at an early age. People have also been feeding them more for faster growth. “This is why we’ve been seeing more DOD problems since the 1950’s, when the horse was converted from an animal of work and war to a recreational animal or competitive athlete,” says Schramme.
There is also some indication that foals born earlier in the year are at higher risk, especially in climates where it’s not possible to turn them out that early. “In a cold climate, early foals won’t have the benefit of turnout and exercise, and this seems to predispose them to more problems. Natural exercise is one important factor, along with nutrition. In Kentucky, they
found that early foals are more prone to hock OCD and later foals more prone to stifle OCD. This may have something to do with exercise
or the contents of spring grass compared to summer grass. There are many factors involved; there is usually no single, obvious cause or reason for DOD.”
Schramme says there are generally four causes, and each case is usually a combination of some or all of them. “The four causes are genetic predisposition; rapid growth (which includes growth spurts--which may occur when foals catch up after stress of weaning, illness
or some other factor in which growth was temporarily slowed); nutrition (high energy intake, copper shortage, calcium/phosphorus imbalances); and trauma—too much exercise and overload,” he explains.
“This last cause, exercise and trauma, is open to a lot of debate: do you need to confine foals or exercise them? There have been studies with contradictory results, but most people feel it is better to provide foals with free turnout than to confine them completely or to confine them and give them short bouts of high-speed activity. Joint cartilage of foals that have not received access to free turnout has lost the ability to adapt functionally to
the load placed on it, once the foals reach 5 months of age. Once cartilage has lost the ability of adaptation, it’s more apt to become injured and degenerate quicker. The best way to help those tissues to adapt functionally
(to produce cartilage heterogeneity, which means that in different places in the joints
the cartilage adapts in different ways to the load placed upon it) is to allow the foal free exercise in the first 5 months of its life.” The
healthiest option is to mimic nature and let the foals run free.
This can sometimes have negative effects, however. One-way foals become injured is when mares and foals are first turned out, after leaving the foaling stall. The mare goes tearing around the pasture and the foal tries to keep up with its mother. “That’s when they strain or break things. This risk can be minimized
by sedating the mare for that first turnout or going gradually to the large pasture (a small turnout paddock first) to avoid the sudden tearing around. Even with those exceptions, it is better for foals to be out, rather than stall- bound,” Schramme says.
Regarding genetics, stallions with OCD will produce foals that are 1.5 times more likely to have OCD than foals born from parents without OCD. “Genetically there is also an overlap between genetic predisposi- tion and rapid growth. There is a further crossover between rapid growth, excess body weight and the trauma sustained by joints during weight bearing,” he says. So, all four causes may be interrelated.
In terms of prevention, we must look at each of these causes, and every new piece of information related to each of these four cor- nerstones. “To some extent we can reduce the incidence of these diseases by not using affected animals for breeding,” Schramme says. “Some stud books are actively promoting the fact that they can guarantee the offspring of certain stallions will not have OCD. Although some claim they are close to identifying the genetic marker for OCD, it must be remembered that the condition is multi-factorial and therefore may not be dependent on one gene.”
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