North American Veterinary Licensing Examination (NAVLE) Practice Test

A cow on a diet low in thiamine is at risk for developing polioencephalomalacia. This condition is primarily caused by a deficiency of thiamine (vitamin B1), which plays a crucial role in energy metabolism and neurological function. When thiamine levels are inadequate, it can lead to severe neurological symptoms due to the impaired function of the brain, particularly the cerebral cortex. Polioencephalomalacia is characterized by the softening of brain tissue and can cause clinical signs such as depression, ataxia, and recumbency. The deficiency often results from diets high in carbohydrates, which lead to the overgrowth of thiaminases-producing microorganisms in the rumen or from the consumption of feedstuffs that are low in the vitamin. In contrast, the other conditions listed are not directly related to thiamine deficiency. Parturient paresis relates to calcium deficiency during late gestation or early lactation. Downer cows can arise from a variety of causes, including metabolic disorders, trauma, or infections, and pseudorabies is a viral infection not associated with thiamine levels. Therefore, thiamine deficiency specifically correlates with the development of polioencephalomalacia in cows.