Even with advances in equine medical technology, there are still many challenges involved in raising a healthy, sound horse. Among them are a group of particularly debilitating bone disorders known as Developmental Orthopedic Diseases (DOD), which are affecting an increasing number of young horses. DOD can seriously jeopardize growth and performance, causing considerable expense and even heart-wrenching, life-or-death decisions. Despite a great deal of research, prevention remains elusive.
In order to minimize the risk of DOD, it is first necessary to understand the dynamics of normal bone development. A foal’s skeletal structure is initially composed of cartilage. As the foal matures, cartilage cells are eventually replaced by hard bone, through a process called endochondral ossification. Problems often result from the lack of essential nutrients supplied by the blood to the cartilage, which consequently causes an interruption of the development process and ultimately compromises growth.
Developmental Orthopedic Disease
Defined as any disturbance to the skeletal cartilage, the precursor to bone development, DOD is the general term for six distinct disorders outlined below:
1. Osteochondrosis dessicans—Thickened cartilage or bone fragments usually involving a joint or bone cyst that may or may not come into contact with the joint
2. Osteochondrosis of the vertebral column—A malformation of the spinal vertebrae producing an alteration of gait due to spinal cord impingement, also known as “wobblers” syndrome
3. Epiphystitis/physitis—Inflammation of the growth plate, as characterized by such conditions as “open knees” or “hourglass fetlocks,” seen as an enlarged ridge just above or below a joint
4. Flexural deformities—Whether congenital (present at birth) or acquired, flexural deformities such as “buck knees,” “contracted tendons,” “club feet,” and “knuckling over” are the result of poor bone formation and pain
5. Angular limb deformities—Valgus conformation (“knock-knees” or “cow hocked”) or varus conformation (“bow legged”) reflects poor bone formation and unbalanced strength of the limb
6. Cuboidal bone malformation—Shows up as limb weakness and laxity; affects foals born with underdeveloped bones in the knees or hocks.
Reducing the Risks of DOD
While there is no one definitive cause, there is a great deal of speculation that the interaction between genetics, nutrition, and management plays a significant role in determining the incidences of this potentially crippling disease. To help the small or large horse owner or manager determine a sound breeding program, recent scientific findings point to several considerations that help reduce the threat of permanent disfigurement or chronic lameness.
1. The Genetic Component
Unfortunately, DOD is thought to be hereditary. According to a number of studies, certain stallions produce a higher rate of incidences than others, and when stallions with this predisposition are bred to predisposed mares, a considerable majority of the resulting foals show signs of DOD disorders. Furthermore, horses with an inherent tendency toward rapid growth spurts also are thought to be at risk.
2. The Nutrition Component
A balanced nutritional program, however, can help to forestall problems for the rest of the equine population. Start early by providing the proper nutrients to the pregnant mare. During the last 90 days of gestation, when the foal’s development quickly accelerates, her energy needs (caloric intake) increase by 20 percent, her protein needs go up 35 percent, and her calcium and phosphorus needs escalate by 90 percent; therefore it is essential to the future of both foal and mare that they receive adequate nutrition.
“Recent scientific studies have determined that stall confinement for as little as two weeks will lower bone density…”
As the foal matures, it is essential to maintain the balance of protein, calcium, and phosphorous in relation to energy for optimum growth and skeletal development. An imbalance of these nutrients, especially from a disproportionately high energy diet, is believed to compromise structural integrity and contribute to DOD.
3. The Exercise Component
To achieve optimal growth rates, combine an exercise schedule with a sound feeding program. Recent scientific studies have determined that stall confinement for as little as two weeks will lower bone density; without sufficient exercise (“bone loading”), the risk of DOD increases. Activity level greatly determines a foal’s energy needs—the feeding requirements for a foal who is receiving adequate exercise would be excessive for a foal who is stallbound or restricted to a small paddock.
A model exercise program would integrate short periods of high-energy work on a firm ground surface with moderate exercise and free turn-out time where the footing is soft. The latest findings show that foals from the ages of three to 24 months, with a tendency toward rapid growth, who were galloped or trotted for 15 to 45 minutes, five days a week, showed fewer signs of DOD than foals who were walked.
Note: Avoid sudden changes to or increases in the exercise program. Intensive training sessions without adequate preparation may lead to indications of “bone overload,” resulting in lameness or inflammation and leading to permanent disability. If exercise is delayed or postponed for a long period of time, re-introduction should be gradual to reduce the possibility of trauma.
• Have your hay and feed analyzed annually to determine nutrient values. A university extension specialist, nutritionist, or feed representative should be able to assist you.
• Provide small, frequent meals (creep feeding) to nursing foals between one and two months of age, along with all the hay or pasture they will eat. Creep feeding should be introduced slowly and with careful monitoring.
• Provide mares with adequate prenatal nutrition.
• Use common sense when exercising foals. Avoid abrupt changes to workout schedules and allow for adequate turnout time over large areas of ground.
• Regularly examine foals for inflammation, injury, lameness, gait changes, etc.
While most experts agree that Developmental Orthopedic Diseases are likely something a young horse is predisposed to thanks to genetics, there are some measures we can take to minimize their impact.