STUDIES ON PREGNANCY DIAGNOSIS IN DOMESTIC ANIMALS BY AN ULTRASONIC DOPPLER METHOD : I PREGNANCY DIAGNOSIS IN THE PIG AND FETAL HEART RATE CHANGES DURING PREGNANCY

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A portable ultrasonic fetal heart detector, Heart-tone Model USD-I (Aloka Co. Ltd., Tokyo), with a 2.25 MHz probe was used for a study of pregnancy diagnosis in swine. The animals to be examined were placed lying on the pen floor with neither fixation nor anesthesia. The probe was gently applied on the skin of the lower abdomen or the flank. Ultrasonic Doppler signals based on the fetal circulation were heard by the operator and at the same time recorded on magnetic tapes to aid fetal heart rate calculation. The maternal circulation was easily distinguishable from the fetal circulation by the considerably slower rhythm of the former. The accuracy of diagnosis was based on delivery. A total of 83 experiments were carried out on 70 sows of 4 different breeds from 22 days post-coitum to the full term. Before 30 days post-coitum, the accuracy rate for pregnancy diagnosis was not satisfactory (58.3%). However, it became higher during the period from 30 to 39 days (81.8%). After 40 days of pregnancy, the accuracy rate of diagnosis reached 100 percent. The earliest detection of pregnancy by this method was in a case of 26 days after copulation. A highly significant negative correlation was observed between the fetal heart rate and the fetal age. The correlation coefficient was- 0.87 (P<0.01). The fetal heart rate became slower in a negative linear regression as gestation progressed ; Y=252.6-0.572X (X=Fetal age, Y=Fetal heart rate).
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