THE ORIGIN OF THE EQUINE ENDOMETRIAL CUPS

Abstract

The gonadotrophin (pmsg) present in the serum of mares between the 40th and 120th days of pregnancy originates in the uterine endometrial cups. These structures begin to develop on the 36th day of pregnancy opposite a transitory, though well-defined, circumferential thickening of the chorion called the allantochorionic girdle (Ewart, 1897; van Niekerk, 1965; Allen, 1970). The endometrial cups are composed of a discrete and densely packed mass of very large, epithelioid, decidual-like cells. They develop before the allantochorion becomes attached to the endometrium and it has been widely accepted in the past that they are exclusively maternal in origin (Clegg, Boda & Cole, 1954; Amoroso, 1955). However, recent genetic evidence, derived from the study of interspecific equine hybrids, has indicated