Occipitoatlantoaxial malformation in two non-Arabian horses.

The study describes two cases of Occipitoatlantoaxial malformation, a rare neurological condition, in non-Arabian horses — a 19-month-old Appaloosa mare and a 3-year-old Quarter Horse gelding. Although both horses displayed abnormal head and neck positions since birth, neurological symptoms only began to appear when they reached 2 and 3 years old, respectively. Diagnosis methods included physical examination and X-rays, which showed fusion of certain neck bones and modifications of the atlas and axis. These findings were later confirmed via autopsy.

Research Context

• This research is focused on diagnosing Occipitoatlantoaxial malformation, a rare neurological condition, in horses. While this diagnosis is unusual, it has critical implications as it affects the horse’s motor abilities and overall health.
• The study brings attention to two non-Arabian breeds, an Appaloosa mare and a Quarter Horse gelding. They were exhibiting abnormal head and neck posture since birth, but neurologic deficits only became evident when they reached 2 and 3 years old respectively.

Diagnosis Methods

• The researchers made their diagnosis through a physical examination, specifically the palpation and manipulation of the neck and base of the skull. In both cases, movement could not be elicited at the atlantooccipital joint—a joint in the spinal column that allows the head to move up and down. However, the range of dorsoventral motion at the atlantoaxial joint—another crucial joint in the neck that permits the head to turn from side to side—was increased when compared with clinically normal horses.
• Noticeable clicks could be heard when the atlantoaxial joint was manipulated, indicating that it was subluxating (partially dislocating) and relocating.
• Radiography, or X-rays, were used to further investigate the condition. This revealed a symmetric fusion at the atlantooccipital joint, with the atlas (the first cervical vertebra which supports the head) and the axis (the second cervical vertebra which allows the head rotation) showing modifications. This kind of fusion and modification of the cervical area is symptomatic of Occipitoatlantoaxial malformation.

Post-mortem Confirmation

• The aforementioned findings were subsequently confirmed at necropsy (autopsy for animals). This allowed the researchers to conclude with certainty that the horses suffered from Occipitoatlantoaxial malformation.

Significance of the Study

• This research adds to the understanding of Occipitoatlantoaxial malformation in non-Arabian horses, which was not extensively studied before. It also provides valuable insights for veterinary practitioners to diagnose this condition in its early stages using physical examination and radiography.
• Early diagnosis and understanding of this malformation can contribute to better management of the horses’ health and potentially provide better therapeutic strategies to improve their quality of life.