Q: What is metabolic bone disease and what do we know about this condition?

A: Metabolic bone disease is now called developmental orthopedic disease (DOD). The reason for the name change is that some of the conditions that were included under the term were determined to not be due to metabolic problems. Developmental orthopedic disease includes: epiphysitis (physitis), osteochondrosis (OC), osteochondritis dessicans (OCD), angular limb deformity, some forms of wobblers, and a number of other limb related abnormalities. It has been established that each of these conditions may be caused by one or more factors. Those factors considered to be the major contributors include: genetics, nutrition, stress and perhaps environment. For example, a growing horse fed a high concentrate diet that has a genetic propensity to deposit muscle and fat more rapidly than bone may be vulnerable to epiphysitis. This condition is the inflamation of the growth plate caused by the stresses on the plate exceeding its ability to tolerate that stress. The condition may be aggravated by hard or rough ground and exercise.

Osteochondrosis and OCD are of particular concern to some breeders and trainers because these defects in the joint cartilage can render the animal lame and unable to tolerate training. Some of our research suggests that foals may develop these problems by the time they are 3 - 4 months of age. A recent study by Coehen et al (2003) from Hanover, Germany on the causes of these problems in Hanovarian horses on private farms provided the following information. The incidence of the condition was high, as 222 foals out of 629 were detected to have osteochondrotic lesions in one or more joint. A review of the nutrition programs on the farms producing these foals revealed that 71% of the mares were fed less digestible protein and 51% were fed less energy than recommended. There was also a tendency for mineral intake to be inadequate on some farms. However, there was no relationship between nutrient intake of mares or their foals and the incidence of OC. It was common for farms to have both normal and OC foals on the same feeding program. This suggests that the dominant factor may be genetic propensity for the problem. The low nutrient intake of some of the mares may be an effort by the farm to reduce growth rate of their foals because they have experienced problems in the past. It is important to understand that lowering the energy and protein intake of the animal may be appropriate when they show signs of having problems because weight may aggravate the condition. However, nutrient imbalance is never appropriate. This will cause the animal to build poor quality tissues that will delay healing and may increase the magnitude of the problem.