The first clinical sign of PEM is loss of vision. By using their other senses, animals with PEM may still be with the herd, so it may be hard to notice this condition in the early stages. Sometimes they will have an exaggerated gait and pick their legs up higher with uncertain steps when walking. As it progresses, many times their head will be elevated and it appears they are looking blankly into the sky, hence the term "star gazing." Over the course of hours, the animal becomes recumbent (unable to stand), then begins to have uncontrollable seizures. The later symptoms may be difficult to distinguish from a listeria infection (see listeriosis fact sheet).

As these symptoms develop from the lack or interference of thiamine, it is not surprising that the treatment is administering thiamine injections. Thiamine should be administered intramuscularly (IM), twice daily, for a minimum of three days. Supportive treatment includes anti-inflammatories such as dexamethasone to decrease swelling of the brain. Also, if the animal is not eating, drenches are beneficial to increase nutrition until medications work. Antibiotics are frequently given for two reasons, they may be given prophylactically or to prevent bacterial infections in the inflamed tissues. Or in the late stages of the disease symptoms closely resemble some of those of the bacterial disease listeria, if the diagnosis isn't certain the antibiotics should be used. Treatment is much more effective when the disease is recognized early. Once the animal is recumbent or seizing, the overall prognosis becomes poor. The rapid progression of the disease makes it challenging. Unfortunately, nerve and brain tissues do not regenerate well once damaged. Even many animals that do recover may have residual damage such as permanent vision loss.

regenerate well once damaged. Even many animals that do recover may have residual damage such as permanent vision loss.

As we talk about prevention, remember that this is a nutritional disease. Sheep and goats need to have an adequate and balanced diet, especially in young animals that do not have a fully matured rumen yet. In adult animals, we need to keep the rumen happy with fiber sources to prevent acidosis or sudden changes that may upset the microbe populations or functions. Avoid weeds in pastures that may have a thiaminease activity. Prevent feeding diets that are in excess of 30% byproducts. Monitor animals closely for any signs of illness. The initial signs of vision loss may be very subtle when looking at an animal in a large group; however, there is a huge difference in prognosis if the animal is not noticed for 24 hours. While it may not be possible to avoid ever having animals with PEM, cases should be rare. By understanding the symptoms and early recognition, it is a manageable disease.

https://www.merckvetmanual.com/nervous-system/polioencephalomalacia/overview-of-polioencephalomalacia https://www.agric.wa.gov.au/livestock-biosecurity/thiamine-deficiency-induced-polioencephalomalacia-pemsheep-and-cattle

https://www.canr.msu.edu/sheep_goats/health/polioencephalomalacia

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