Blain was an animal disease of unknown etiology that was well known in the eighteenth- and nineteenth centuries. It is unclear whether it is still extant, or what modern disease it corresponds to.
According to Ephraim Chambers' eighteenth-century Cyclopaedia, or an Universal Dictionary of Arts and Sciences, blain was "a distemper" (in the archaic eighteenth-century sense of the word, meaning "disease") occurring in animals, consisting in a "Bladder growing on the Root of the Tongue against the Wind-Pipe", which "at length swelling, stops the Wind". It was thought to occur "by great chafing, and heating of the Stomach".
Blain is also mentioned in Cattle: Their Breeds, Management, and Diseases, published in 1836, where it is also identified as "gloss-anthrax". W. C. Spooner's 1888 book The History, Structure, Economy and Diseases of the Sheep also identifies blain as being the same as gloss-anthrax.
Modern scholarship suggests that "gloss-anthrax" was not the same disease as modern-day anthrax, but instead could have been foot-and-mouth disease, or a viral infection with a secondary Fusobacterium necrophorum infection. It has also been suggested that it may have been due to a variant strain of true anthrax that is no longer in existence. Other sources also report epizootics known as "blain" or "black-blain" in the 13th and 14th centuries, but it is not clear if the disease involved was the same as "gloss-anthrax".