Catgut is commercially made from the intestine of the following animal:

Gut sutures derived from sheep submucosa or beef serosa are digested by proteolytic enzymes in the wound. They are more rapidly degraded in the presence of infection. The knot-holding ability of plain gut is rather inconsistent; chromic gut seems to be better in this regard. Plain gut--Plain gut incites an intense inflammatory reaction in the wound and loses its tensile strength within 2 weeks. Chromic gut--Treatment of gut with chromium salts decreases its tissue reactivity and prolongs its survival to about double that of plain gut. Ref: Jones T.R. (2011). Chapter 30. Wound Care. In R.L. Humphries, C. Stone (Eds), CURRENT Diagnosis & Treatment Emergency Medicine, 7e.