Ultrasonographic appearance of the bovine conceptus from days 10 through 20

The bovine conceptus was monitored in 19 heifers by intrarectal ultrasonic imaging from the day an embryonic vesicle was first detected (mean, day 11.7 +/- 0.4; range, days 10 to 17) until detection of the embryo proper (mean, day 20.3 +/- 0.3). Fifteen heifers maintained the conceptus and 4 heifers apparently lost the conceptus. In the heifers that maintained the conceptus, 73% of the embryonic vesicles were classified as spherical (mean diameter, 2.8 +/- 0.2 mm) and 27% were classified as oblong (mean dimensions, 2.0 +/- 0.0 mm and 4.5 +/- 1.0 mm) on the day of first detection. All vesicles were in the uterine horn ipsilateral to the corpus luteum. The vesicles increased in length from the day of first detection. On the average, the vesicle occupied all of the ipsilateral uterine horn on day 16.9 +/- 0.6 and all of the contralateral horn on day 19.6 +/- 0.9. During elongation, the vesicle remained at an approximate height of 2 mm throughout its length, but developed a localized enlargement or bulge on mean day 19.7 +/- 0.2. The embryo proper was detected within the bulge in all 15 heifers. A heartbeat (mean, 188 +/- 4.8 beats/min) was detected on the first day of detection of the embryo proper (8 heifers) or on the following day (7 heifers). The mean length of the interovulatory interval in the 4 heifers that apparently lost the embryonic vesicle was not significantly different from that of nonbred heifers. The vesicles were lost (not ultrasonographically detectable) on days 17 (2 heifers) and 19 (2 heifers).(ABSTRACT TRUNCATED AT 250 WORDS)