Murrain (also known as distemper) is an antiquated term for various infectious diseases affecting cattle and sheep. The word originates from Middle English moreine or moryne, as a derivative of Latin mori "to die".

The word murrain, much like the word pestilence, did not refer to a specific disease but rather was an umbrella term for what are now recognized as a number of different diseases with high morbidity and mortality, such as rinderpest, erysipelas, foot-and-mouth disease, anthrax, and streptococcus infections. Some of these livestock diseases could also affect humans. The term murrain also referred to an epidemic of such a disease. There were major sheep and cattle murrains in Europe during the 14th century, which, combined with the Little Ice Age, resulted in the Great Famine of 1315–1317, weakening the population of Europe before the onset of the Black Death in 1348.