Clostridia can cause a great variety of different diseases both in domestic and wild animals. The diseases caused in livestock are economically very important, as too are those caused in animals held by research or breeding establishments. This chapter discusses the many diseases of the gastrointestinal (GI) tract that can be attributed to Clostridia. There are numerous reports of spontaneous type A enterotoxemia in animals. C. perfringens type C can cause enterotoxemia in a variety of animals species, it most commonly affects sheep, lambs, calves, piglets, and fowl. The isolation of C. carnis or a very similar organism from muskrats and mink has been infrequently reported. C. septicum causes a disease in sheep known as "braxy", and usually affects lambs during the first year of life, especially those on farms in mountainous areas. The organism is sensitive to penicillin, which is typical of Clostridia, and E. E. Tyzzer claimed to have grown the bacterium in an anaerobic atmosphere.