EQUINE FETAL KINETICS - PRESENTATION AND LOCATION

The extent and nature of fetal mobility (presentation and location changes) were studied in 10 pony mares by ultrasonic examinations each week during the fetal stage (Day 40 to term). The percentage of examinations with cranial fetal presentation was 35 to 43% during Months 2 to 5 (no significant differences among months); a significant increase occurred between Months 5 and 6 reaching 100% at Month 7. With only 3 transient exceptions, the fetus was in cranial presentation during all examinations from Month 7 to term. The frequency of presentation changes between successive examinations decreased (P<0.05) between Months 4 and 5 and further decreased between Months 6 and 7. A significant and progressive decrease in the proportion of examinations in which at least part of the fetus was located in the umbilical-cord horn occurred over Months 2 to 4. During the same months, an increase occurred in the frequency of location of at least part of the fetus in the noncord horn and in the frequency of location of all of the fetus in the uterine body. The fetus was equally distributed among the 3 parts of the uterus during Month 4. Thereafter, locations decreased (P<0.05) in the noncord horn, increased (P<0.05) in the uterine body, and maintained a plateau (no significant differences) in the cord horn until Month 7 and then increased (P<0.05). The frequency of location changes between successive examinations increased (P<0.01) progressively during Months 2 to 4 followed by a decrease between Months 4 and 10. With one exception, the fetus was located in both the cord horn and uterine body for all examinations during Month 9 to term. In conclusion, a gradual decrease in fetal mobility occurred after Month 4; with only a few transient exceptions, final selection of cranial presentation occurred by Month 7, and final selection of partial location in the cord horn occurred by Month 9.