Ultrasonographic appearance of the bovine conceptus from days 20 through 60

The ultrasonographic appearance of the conceptus on days 20 to 60 was determined by daily examinations in 15 heifers. The mean length of the embryo proper increased from the day of first detection (day 20.3 +/- 0.3; 3.8 +/- 0.3 mm) to day 60 (66.1 +/- 1.7 mm). The growth curve was quadratic, with an increasing growth rate after approximately day 50. The embryo initially had the appearance of a short, straight line and developed a C shape on day 25.4 +/- 0.8 and an L shape on day 32.7 +/- 1.1. The average day of first detection of various structures was as follows: allantois, 23.2 +/- 0.3; spinal cord, 29.1 +/- 0.5; forelimbs, 29.1 +/- 0.3; amnion, 29.5 +/- 0.5; optic area, 30.2 +/- 0.4; hindlimbs, 31.2 +/- 0.3; placentomes, 35.2 +/- 1.0; optic lens, 40.0 +/- 0.6; split hooves, 44.6 +/- 0.7; fetal movements, 44.8 +/- 0.8; and ribs, 52.8 +/- 0.5. Embryonic death, as indicated by cessation of heartbeats, occurred in one heifer on day 26. The embryonic mass increased in echogenicity and was maintained with a gradually decreasing fluid volume until the occurrence of estrus 17 days after death.