Background <p>The present case report describes the clinical and pathological outcomes of an outbreak of piglet mortality and neuromuscular disorders in newborn and nursery piglets caused by vitamin B5 deficiency.</p> Case presentation <p>A farrow-to-wean 750 sow-farm in Spain experienced abortions and respiratory signs in sows related to swine influenza during the first week of February 2025. It was followed by an unusual high piglet mortality rate within the first week post-farrowing, reaching up to 65% and persisting for seven weeks. Piglets were born apparently healthy, and colostrum intake was considered normal. Nevertheless, on the second day of life, they started showing apathy, ataxia, and prostration, most of them usually dying spontaneously on the third day of life. At the same time, at least 14 recently weaned piglets exhibited similar clinical signs and subsequently died. However, sows were completely unaffected. Initial antibiotic treatments were ineffective. Seven piglets were subjected to a complete necropsy. Five showed the above-mentioned neurological signs and two were completely healthy, which served as non-affected control animals. No relevant gross lesions were found. Histopathologically, neuronal bodies from cervical, thoracic, and lumbar spinal cord had variable degrees of central chromatolysis, cytoplasmic vacuolation, and swelling, with displaced nuclei and occasional necrosis. Some of the sampled sciatic nerves had mild-to-intense axonal swelling and fragmentation. Microscopic lesions were absent in the two non-affected pigs. Pantothenic acid deficiency was presumptively diagnosed, and all newborn piglets were treated with a vitamin B complex. The condition did not re-appear after treatment.</p> Conclusions <p>Insufficient pantothenic acid intake should be among the differential diagnoses of piglets with ataxia, muscle weakness and mortality. A fast diagnosis based on complete nervous system sampling is key to diagnose and counteract this condition.</p>