Gross and ultrasonic morphology of the equine conceptus on days 10 to 40

The gross and ultrasonic equine embryo morphology are described with emphasis on specific days after ovulation. Included are labeled colored photographs and detailed descriptions of the embryo proper (future fetus and foal) and of the entire embryonic vesicle on Days 21, 24, 30, 35/36, and 40. A few related aspects are included for the early fetus on Days 45 and 50. Regression lines for growth in the length of the embryo proper and diameter of the embryonic vesicle along with the mean days of the morphological event are included. Ultra-sonograms of the embryonic vesicle are shown and discussed from Days 10 to 45. Major morphological changes in the embryo proper include: (1) appearance of forelimb and hindlimb buds, (2) appearance of the pontine flexure, (3) appearance of the genital tubercle, (4) closure of the pontine flexure, and (5) tapering of limbs to-ward the midline with hoof-shaped tips. Major changes in the embryonic vesicle are: (1) vascularization of mesoderm, (2) appearance of sinus terminalis, (3) emergence of allantoic sac, (4) formation of embryonic circulatory system, (5) formation and maturation of chorionic girdle, and (6) transition from yolk sac to allantoic sac.

Automated summary

This article describes the morphology of equine embryos with an emphasis on specific days after ovulation. It includes detailed descriptions and labeled colored photographs of the embryo proper and embryonic vesicle at different stages of development. It also discusses the major morphological changes in the embryo proper and the embryonic vesicle, as well as the growth regression lines and mean days of these morphological events.