Strangulation obstruction was induced in anesthetized ponies for periods of 2 and 3 hours by clamping 45-cm segments of jejunum and associated veins (venous strangulation obstruction) and arteries and veins (arterial and venous strangulation obstruction). Four segments were studied in each of 7 ponies allowed to survive 12 hours, 2 segments in a pony that was allowed to survive 1 hour, and 1 segment in each of 10 ponies allowed to survive 42 days after the strangulation periods ended. Fifteen minutes after the periods of strangulation obstruction ended, the viability of test segments was assessed by clinical judgment (40 segments), fluorescein fluorescence (40 segments), and Doppler ultrasound (32 segments). Because thetest segments were normal at necropsy in long-term survivors, all segments were designated as viable. The overall accuracy of the methods used to predict viability was 88% for Doppler ultrasound and 53% each for clinical judgment and fluorescein fluorescence (P less than 0.005). Failures in the last 2 techniques could be attributed to their tendency to score venous strangulation obstruction segments as nonviable (90% for each). Doppler ultrasound was 94% accurate in these segments.

The umbilical arteries urachus, and umbilical vein were scanned ultrasonographically in 13 clinically normal foals that ranged in age from 6 hours to 4 weeks. Sonograms were obtained using a 7.5-MHz sector scanner transducer placed across the midline of the ventral portion of the foal's abdominal wall. The umbilical vein was scanned from the umbilical stalk to its entrance into the hepatic parenchyma. The mean (+/- SD) diameter of the umbilical vein was 0.61 +/- 0.20 cm immediately cranial to the umbilical stalk, 0.52 +/- 0.19 cm midway between the umbilicus and liver, and 0.6 +/- 0.19 cm at the liver. The urachus and umbilical arteries were scanned from the umbilical stalk to the apex of the urinary bladder and had a mean total diameter of 1.75 +/- 0.37 cm at the bladder apex. The umbilical arteries also were scanned along either side of the bladder and had a mean diameter of 0.85 +/- 0.21 cm. These measurements and the ultrasonographic appearance of the internal umbilical structures from clinically normal foals can be used as references to diagnose abnormalities of the umbilical structures in neonatal foals.