North American Veterinary Licensing Examination (NAVLE) Practice Test

The most likely cause of symmetric ataxia and weakness in a 1.5-year-old horse is Equine Degenerative Myeloencephalopathy (EDM). This neurological condition is associated with deficiencies in vitamin E, which is crucial for maintaining healthy nerve function. Horses affected by EDM often display progressive ataxia, which means a lack of coordination, and muscle weakness due to degeneration of the spinal cord and spinal tracts.

What sets EDM apart from other conditions in the list is its age of onset typically occurring in young equines, usually between 6 months and 3 years of age. The clinical signs of symmetric ataxia are also prominent in EDM, as opposed to the more variable presentations seen in conditions like Equine Protozoal Myeloencephalitis (EPM) or botulism. In the case of botulism, while it can cause weakness, it is more commonly associated with acute onset of signs and may involve cranial nerve dysfunction, which is not typically the case with EDM.

Understanding the condition's pathogenesis and presentation is crucial in differentiating it from other similar neurological issues. In summary, EDM aligns with the age and clinical signs presented in this horse, making it the most likely cause of the