Factors other than nutrition affect a foal's normal growth rate and proper development

by Heather Smith Thomas

THE FIRST MONTHS of life are crucial for a foal's future growth and soundness. His skeleton is growing rapidly, especially during the first weeks, and must adjust to increasing stresses from weight and exercise. Failure to recognize and intercede in certain pathologies may adversely affect normal growth and future performance.

Troy Trumble, D.V.M., Ph.D., assistant professor of large-animal surgery at the University of Florida's College of Veterinary Medicine, said that during the first month of life, foals are vulnerable to anything that alters normal growth rate. They still are adjusting to their environment and are somewhat compromised immunologically because they are dependant upon maternal antibodies until their own immune systems develop more. If a foal is born with or acquires an abnormality or disease that affects the musculoskeletal system, rapid adjustments often must be made in care, management, and treatment to allow the foal to grow and respond in normal fashion. Any problems that arise when a foal is young must be identified early so they can be dealt with quickly and properly.

Infections

Young foals are at risk for septic arthritis, joint infections caused by a systemic infection that gains entry through the umbilical stub (navel ill) or from septicemia due to a disease such as salmonella.

"Sick foals, such as dummy foals or those that experienced difficult birth, tend to have a harder time fighting off infections, and these infections may end up in the joints," Trumble said.

If not diagnosed early and treated quickly, these conditions are difficult to reverse soon enough to enable the foal to grow up sound and athletic.

"When a foal is sick, he doesn't want to stand up much or move around and may end up with contractural and flexural deformities," Trumble said. "He is not putting weight on the limb that would help straighten the leg. Foals may have multiple issues at this stage, and it's not uncommon to have multiple joints affected."

Growth rate also may be affected. Some of these compromised foals may be slow to reach their potential. "A lot of these babies that have problems are also premature, and not as immunologically competent--more vulnerable to many things," he said.

Fractures

Fractures can adversely affect a foal's growth if they occur around or through a growth plate.

"We call these Salter-Harris fractures," Trumble said. "If they fracture through a growth plate, the growth at the end of that bone is finished. This can affect how much that particular bone will grow. The higher up the leg a fracture is, the more serious. Often, if we're trying to resolve a fracture, we have no choice but to close that growth plate with screws, plates, etc. for the fracture to heal.

"But, here again, Mother Nature has a way to counteract a problem. If one growth plate closes, growth at the other end of the bone speeds up to make up for it, or some of the other bones grow more," he said. The final length of the limb may be comparable to that of the opposite limb.

Contractural deformities

"The contractural deformities are often called contracted tendons but identified by which joint buckles forward," Trumble continued. "A carpal contraction produces a knee that's buckled forward. This can also happen at the fetlock joint, pastern, or coffin joint." The more severe the deformity, the more difficult it is to bring it back to normal position. Some of these foals are put into casts or splints to help resolve the deformity.

With premature foals, the problem is compounded. Normal foals are very active; if they are not active, the limbs cannot develop properly. So if the foal does not stand and move around, the leg is not helped by normal weight bearing. Bones and joints need normal loading and stress to develop properly.

"If the foal is only standing for short periods of time, this is very unhealthy because foals grow so fast," Trumble said.

Another deformity that needs to be diagnosed and treated early is hyperextension, such as fetlock joints touching the ground and toes flipping up. This is a common problem for foals that are born premature or dysmature (inadequately developed).

Many normal foals have lax tendons when first born, but as they get up and stand, most improve dramatically in a short time.

"But there are some that don't do so well, and people try to help them by putting extensions on the feet," Trumble said. "If you get the forces going in the right direction, they generally improve."

Angular limb deformity

Foals with angular limb deformities are either knock-kneed (valgus) or bow-legged (varus). "Many foals will straighten on their own," Trumble said. "You don't have to do much to help them. Regarding growth rate, however, you have only a certain time frame for treating these. If the problem involves growth plates at the ends of the long bones and you have to do any surgical correction, you must do it before those growth plates close."

Growth plates close quickest at the bottom of the leg and slowest at the top. The first long bones to stop growing are the cannon bones, and the last to stop are at the radius and tibia, he said.

"If you are talking about fetlocks and must do something surgically, as a general rule you must do it within the first two to three months of life," Trumble said. "By contrast, with the knee you may have six months and can actually make some changes as late as yearling age, but you won't be able to make any radical change this late.

A lot of times correction of a limb problem goes hand in hand with the foal being able to put weight on it and being able to exercise."

Physitis

Physitis, or inflammation of the growth plate, also might affect a young foal's growth. This is often due to the stress of growing too fast, as when a foal that is already genetically programmed for fast growth is stimulated to maximum growth with high-quality feeds.

"The foal is either growing too fast or has loaded the limbs too much, too quickly, as when he's out and running with his mother," Trumble said. "Resulting inflammation in the growth plate may cause the joint next to it to buckle forward. An example would be a buckling at the fetlock joint if there's a physitis at the end of the cannon bone."

This problem is associated with the foal's growing patterns and loads placed on the limb. "So the treatment is often based on reducing inflammation in the area and trying to regulate the degree of exercise while the foal is growing, to balance the exercise, diet, and growth. OCD [osteochondritis dissecans] is a developmental problem that affects young horses but usually comes on later. You don't see this in young foals [a month of age or younger] because it's not to the stage yet where you can see it," he said.

"Any of these limb problems--whether it's laxity, contraction, or angular limb deformity--can really stunt a foal's growth," Trumble said. "If you can correct the problem in a timely manner, that foal will take off and grow more normally."

Heather Smith Thomas is a freelance writer based in Salmon, Idaho, specializing in veterinary and breeding topics.