You are called to evaluate a lamb that is having trouble wal…
You are called to evaluate a lamb that is having trouble walking. The ewe lamb is approximately six months old, and she is the only animal in the group that is abnormal. When she was a week old she had an infection at the site where her tail was docked (amputated as a normal production practice), but it cleared up after the owner gave her some penicillin at the dose on the label. The lamb has been growing well until about a week ago, when the owner noticed she was walking abnormally. On physical examination she is alert and in good body condition. She has a normal rectal temperature, heart rate, and respiratory rate, with no physical exam abnormalities outside the nervous system. A neurologic examination reveals the lamb to have normal mentation, no cranial nerve abnormalities, and normal strength, sensation, and proprioception in her forelimbs. However, she is very weak and ataxic in both hind limbs, and when you try to get her to walk, she sways side to side and falls down into a dog-sitting position. She does have a withdrawal reflex in both hind limbs. Given the history and your examination findings, and assuming no financial constraints, which diagnostic test would you run FIRST to try to rule in the MOST LIKELY cause of this lamb’s signs?