DEVELOPMENT OF HORSE EMBRYOS UP TO 22 DAYS AFTER OVULATION - OBSERVATIONS ON FRESH SPECIMENS

  • 1 January 1982
    • journal article
    • research article
    • Vol. 135  (AUG) , 191-209
Abstract
Embryos (49), unfertilized eggs (20) and other fresh eggs (5) of doubtful status were recovered from 58 pony mares in 122 flushes up to 22 days after ovulation. Horse embryos normally enter the uterus as blastocysts 5-6 days after ovulation. Three features of early embryo morphology became clearer upon comparison with unfertilized eggs of similar ages: early embryos were often ellipsoidal in shape; dispersal of most of a thick gel coat seems to have been hastened by fertilization; gradual disappearance of refractile granules from the perivitelline space inside the zona pellucida was similar in fertilized and unfertilized eggs. A tense, transport, acellular capsule (considered to be different from the zona pellucida) was acquired by the spherical blastocysts within the uterus and persisted at least until a diameter of 34 mm was attained (at 21 days in the present series). The capsule seems to be analogous in part with the neozona described in rabbit blastocyst before attachment, and trophoblastic cells appeared to be involved in its formation. Cleavage stages of oviductal embryos and diameters of uterine blastocysts from this series were described and illustrated, and used to extend previous knowledge of early growth patterns in horse embryos.