The Irish Connemara pony is known for being both athletic and surefooted. But a recently discovered and frustrating hoof condition can strike these ponies down before they even reach weanling age. Fortunately, researchers are making strides in understanding this syndrome, and might have uncovered a way to drastically reduce its incidence.
At the 2013 International Equine Conference on Laminitis and Diseases of the Foot, held Nov. 1-3 in West Palm Beach, Fla., Carrie Finno, DVM, PhD, Dipl. ACVIM, presented recent study results suggesting that Connemara hoof wall separation syndrome (HWSS) is an autosomal recessive trait that can be avoided by careful breeding.
Finno, currently a researcher in the University of Minnesota Equine Neuromuscular Diagnostic Laboratory, explained that the syndrome is characterized by severe hoof wall separation during the first year of Connemara foals' lives.
"The weight-bearing borders of the hoof wall break away from the underlying structure, leaving the pony to bear weight on the sole," she said. And while this condition appears clinically similar to white line disease—which causes a progressive separation of the inner structures from the outer hoof wall in horses of all breeds, ages, and sexes—it only affects Connemara foals aged 1 to 4 months, and it only affects the dorsal hoof wall (the outside of the hoof wall at the toe).
"This is a life-long problem and never resolves," Finno said. "Owners have tried lots of different supplements, frequent trimming, shoes, etc. with limited success."
Recently, Finno and colleagues from the University of California, Davis, and Massey University, in New Zealand, set out to investigate the genetics behind HWSS. The long-term goal is to develop a genetic test for the condition to help veterinarians 1) accurately diagnose affected ponies, and 2) prevent new cases from developing.
The team collected DNA samples, pedigree information, and photographs of 330 Connemara ponies (15 affected by the condition and 315 controls) from around the world. They determined the genotypes (the genetic makeup of a physical trait) of 12 case and 24 control horses, and were able to identify a genome-wide significant candidate region of association (or a specific region of the horses' genome that appears to contain important genetic determinants for the trait being studied– in this case Connemara hoof wall separation syndrome).
Based on their findings, the team concluded that Connemara hoof wall separation syndrome is an autosomal recessive trait. This means that each of the foal's parents appear normal, but carry one normal allele and one defective allele (each gene has two alleles—one inherited from the mother and one from the father). When both parents pass their defective alleles on to the foal (25% chance if both parents are carriers), the foal ends up with a pair of defective alleles, triggering disease expression. In theory, breeders could reduce or eliminate this syndrome's prevalence by testing both parents to determine if they are carriers before breeding.
The team is currently analyzing next generation DNA sequence data from affected and control ponies for significant functional variants and working to develop a genetic test for the condition.
The study, "Clinical and genetic investigation of Connemara hoof wall separation syndrome," was published in October in the Journal of Equine Veterinary Science.