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Genetic Cause of Foal Deformities InvestigatedBy Kentucky Equine Research Staff · October 27, 2011

Many foals are born with some degree of limb deformity. In mild cases, the deformity may be self-correcting as the foal matures, or it may respond well to therapies such as corrective trimming, splinting, or surgery. A more severe level of flexural limb deformity (FLD) can affect several legs and can be serious enough that the foal will never be able to perform normally. In the worst case, known as contracted foal syndrome (CFS), the spine, neck, skull, and all four legs may be grossly abnormal. Many of these foals are euthanized.

FLD and CFS have been reported in Thoroughbreds, Standardbreds, Saddlebreds, Quarter Horses, and other breeds. More than one limb is usually involved, and males are affected somewhat more frequently than females. Mares frequently have difficulty in delivering deformed foals, possibly because the fetus can’t be properly positioned to pass easily through the birth canal.

Research at the University of Kentucky studied DNA samples from foals with CFS and FLD. Preliminary results from the study showed that the deformities have a genetic component that is complex and poorly understood. Multiple genes are probably involved, and it is likely that several factors determine the extent to which the deformities are expressed. Causes may also be related to toxins, dietary balance, uterine conditions during pregnancy, and viral infection.

In the study, management practices did not seem to be a major factor in causing deformed foals. Several mares included in the study had produced as many as four deformed foals. The mares had been housed on various farms and each foal had been sired by a different stallion.

Microscopic examination of tissue samples from the muscles, tendons, and ligaments of affected foals appeared normal.

Teri Lear, Ph.D., who led the research, said many more horses need to be studied before answers are found. Anyone wishing to provide information on deformed foals or find out more about the study can contact Lear at equigene@uky.edu. All information will be kept confidential. 

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