EQUINE FETAL KINETICS - PRESENTATION AND LOCATION

The extent and nature of fetal mobility (presentation and location cha nges) were studied in 10 pony mares by ultrasonic examinations each we ek during the fetal stage (Day 40 to term). The percentage of examinat ions with cranial fetal presentation was 35 to 43% during Months 2 to 5 (no significant differences among months); a significant increase oc curred between Months 5 and 6 reaching 100% at Month 7. With only 3 tr ansient exceptions, the fetus was in cranial presentation during all e xaminations from Month 7 to term. The frequency of presentation change s 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 lea st part of the fetus was located in the umbilical-cord horn occurred o ver 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 ho rn 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 uter us during Month 4. Thereafter, locations decreased (P<0.05) in the non cord horn, increased (P<0.05) in the uterine body, and maintained a pl ateau (no significant differences) in the cord horn until Month 7 and then increased (P<0.05). The frequency of location changes between suc cessive examinations increased (P<0.01) progressively during Months 2 to 4 followed by a decrease between Months 4 and 10. With one exceptio n, the fetus was located in both the cord horn and uterine body for al l examinations during Month 9 to term. In conclusion, a gradual decrea se 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.