Osteochondrosis dessecans, or OCD, is a collection of syndromes that involves disturbed activity in growing bones. The form found in horses refers to a disorder at the level of the subchondral bone, a transition zone between cells that form bone and those that form joint cartilage.
Like anything else, the earlier you detect the problem, the better chance that treatment will help. Watch youngsters from birth onward. If you notice decreased activity, stiffness, unexplained lameness or abnormal joint swelling, get it checked immediately. Prevention involves simple, basic management.
Heredity likely plays a role in OCD, although whether it is a weakness in the cellular function or something like a greater sensitivity to nutritional imbalances is unknown.
Exercise, whether too little and too much, also may cause OCD. Exercise is necessary to stimulate developing bone, but too much hard exercise can harm young bones.
Rapid growth, particularly due to high-calorie diets, may be a risk factor for OCD — or at least it’s often during a period of rapid growth that OCD becomes severe enough to be diagnosed. Rapidly growing and remodeling bones are more easily injured. Rapid growth also places tremendous nutritional demands on the body, making even an adequate diet fall short.
Obesity may predispose a horse to OCD. Nature never intended the young horse’s immature bones to carry the amount of fat often seen on halter and sales horses.
Nutrition is obvious. The young horse should have an overall diet protein level of 14 to 16%. Even more important than the percentage are the correct types of protein, especially lysine, methionine, cystine, cysteine. He needs adequate amounts of the fat-soluble vitamins, which are A, D and E. On the mineral front, calcium, phosphorus and magnesium are equally critical to normal bone development. The trace minerals also play a role in formation of healthy bone and joint cartilage.
While there’s little you can do about heredity — except avoid breeding horses known to have foals with OCD — you can do a lot on the management front.
The ideal condition for growing animals is 24-hour turnout in a large area, preferably with a rolling terrain. Confinement to a stall or small paddock/pen deprives the bones and joints of the constant stimulation they need to develop properly. Close confinement also leads to a lot of dangerous pent-up energy.
A recent study looked at tendon health in three groups of young animals:
1) Those with complete stall confinement,
2) Those with constant turnout,
3) Those with stall confinement for part of the day.
Complete stall confinement led to weakening. The ones on constant turnout had the healthiest tendons. The ones confined for part of the day, then turned out, showed areas of actual tendon damage. The authors believe the exuberant playing this third group did when they got turned out was the cause.
Light formal exercise is beneficial to musculoskeletal development and strength, as long as you don’t overdo it. However, heavy exercise of two-year-olds and even some three-year-olds is inviting trouble — ask any racehorse trainer.
Diets for the growing horse (weanling to three-year-olds) must provide adequate, balanced vitamins and minerals and high-quality adequate amounts of protein. Note we said “adequate,” not excessive. This is often easier said than done.
While most horsemen know diet can cause OCD, they’re confused about how. There is no single grain, protein/mineral supplement or hay that can be recommended across the board for any young animal. There are too many variables to consider.
You may use an appropriate grain mix only to have the balance in the diet thrown off by the hay, or match your grain, supplements and hay but run into problems because of the pasture quality.
Unfortunately, the only way to know for sure the diet is correctly balanced and adequate is to have everything he eats — grain, hay and pasture — analyzed. (Relying on National Research Council average nutrient breakdowns is better than nothing but remains risky because local soil conditions result in wide variations in mineral content of grasses and hays in different areas.)
Pasture Only: Some horsemen simply skip grain entirely and rely strictly on pasture. This isn’t a bad idea if your geographical area allows it. In most cases, high-quality pasture supplies enough calories to support a reasonable growth rate and good body condition while avoiding obesity. You can add grain if the horse becomes too thin.
Fresh grasses, especially the early growth stages, are excellent protein sources, and minerals exist naturally in chelated forms. However, unless you have legumes mixed in the pasture (clover or alfalfa), the amount of the key amino-acid lysine may be too low. Grasses also vary widely in the mineral levels and the ratios of minerals to one another.
If you want to raise your young stock on high-quality pasture alone have your pasture analyzed. The results will tell your nutritionist what minerals and amino acids need to be supplemented. If you’re lucky, you may be able to find a commercial pelleted protein/mineral supplement that fits the bill. (A pelleted supplement eliminates the need to mix it with grain in order to feed it.)
Added Grain: If you must feed grain, either to keep adequate weight or as a carrier for a powdered supplement, choose a mix specially formulated for growing horses.
Added Hay: When hay must be fed, the same amino acid and mineral analysis should be done. If you can’t buy in large amounts or from a single, constant source, analysis is unrealistic. Instead, ask the seller where the hay was grown and then call the agricultural extension agent for that location. He or she may have the figures you need without the expense of constantly having to analyze the hay.
Once you have the needed numbers, the nutritionist can again figure out the supplement levels you need to complement the hay and pasture. When you begin with a correctly balanced base of hay and/or pasture, you can add a grain mix formulated for growth without upsetting the mineral and amino acid balance.
Be careful with commercial grain mixes for growing horses. Some have extra minerals and amino acids to compensate for common shortfalls in hay and pastures. If the tag shows copper levels over 40 to 45 ppm and selenium over 0.2 ppm, this is probably the case. If you’re not sure, call the manufacturer and find out.