Embryo development and placentome formation during early pregnancy in red deer

Early embryo development and placentome formation were assessed in red deer between Days 27 and 55 of gestation. Uteri were collected from 12 pregnant hinds in which mating was observed following a synchronized oestrus, and the tissues retained for measurements and histological processing for light microscopy. Twelve embryos were recovered with mean embryo weights increasing from 0.02+/-0.01 g at Day 27 to 7.56+/-1.39 g at Day 55 of gestation. Similarly, crown-rump lengths increased from 5.7+/-0.7 mm to 55.3+/-5.9 mm over this period. The trophoblast had extended throughout both uterine horns and gastrulation was completed by Day 27. Limb buds were apparent by Day 34, and by Day 48 the phalanges had separated into hooves and dew claws. Plaques were evident on the trophoblast at Day 34 and, by Day 41, placentomes had formed adjacent to the embryo. These placentomes grew in size as pregnancy advanced; by Day 55 most caruncles had formed placentomes. It is therefore confirmed that placentome formation occurs at about the sixth week of gestation. These results indicate that embryo growth and placentome formation in red deer are generally typical of that observed in other ruminants.