OAAM is actually the abbreviation for the congenital condition known as Occipital Atlanto-Axial Malformation that occurs almost exclusively in Arabian horses. This condition results in a fusing of the spinal vertebrae in the neck and where the neck and skull join. The results of this lethal condition may initially be mild to debilitating and severe as the foal will have limited movement of the neck throughout its short life. In severe cases paralysis and extreme lack of coordination will also be noted as the foal tries to move.
OAAM can be diagnosed when the foal is less than one month old although in some cases it can be weeks before it is identified and diagnosed. In early diagnosed cases it is often very severe as the foal is unable to position his or her head correctly to nurse. The spine has fused so tightly at the base of the skull that they are not able to extend the head into the correct position to access the mare. In addition the foal may not be able to stand or to move once he or she is in the standing position. OAAM will cause the gross motor muscles or the large muscles of the body to lack control resulting in poor if any coordination. This lack of coordination results in greater risk of other injuries to the foal.
As the condition becomes progressively worse the foal may experience paralysis in either the front legs or both the front and back legs. As this is a genetically inherited condition there is no way to correct the paralysis or the fusion of the spinal vertebrae, although there have been many different treatment options suggested. There is ongoing research to try to determine the exact genetic makeup that produces Occipital Atlanto-Axial Malformation in Arabians, but at this time there is no conclusive evidence.
Occipital Atlanto-Axial Malformation is different from Cerebral Abiotrophy or CA in that there is no related neurological degeneration as seen in CA. Often Arabian foals that do not exhibit any symptoms of OAAM until after the first month are misdiagnosed with CA. An examination after death of the brain and formation of the neck and spinal column at the base of the skull can clearly identify which genetic disease was the cause of death and paralysis.
Many Arabian breeders are actively working with researchers at major vet colleges and universities to try to establish the genetic links with both CA and OAAM. Since the diseases are genetic in nature and progressive, both resulting in death, they must be recessive genes that allow horses in the population to act as carriers without showing any signs of the lethal conditions. Further research and the efforts of Arabian breeders will be required to determine testing mechanisms that can help select breeding lines that are clear from the conditions.
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