“…Animals in which the presence of the uterus is important for cyclic ovarian activity include the cow (Wiltbank & Casida, 1956), sheep (Wiltbank & Casida, 1956), pig (du Mesnil du Buisson & Dauzier, 1959) and guinea-pig (Loeb, 1923). In the mouse (Bartke, 1970), rat (Bradbury, Brown & Gray, 1950), hamster (Caldwell, Mazer & Wright, 1967) and rabbit (Asdell & Hammond, 1933), hysterectomy does not affect cyclic ovarian function but does result in prolongation of the pseudopregnant state. Recently,344 G. H. Stabenfeldt et al evidence has been presented that hysterectomy prolongs the life span of the CL in the non-pregnant mare (Ginther & First, 1971).…”