Pregnancy Diagnosis in Swine by an Ultrasonic Doppler Method and Fetal Heart Rate Changes with Progress in Pregnancy

Abstract

A portable ultrasonic fetal heart detector, Hearttone Model USD-I (Aloka Co., Ltd., Tokyo), with a 2.25 MHZ transducer was used for a study of pregnancy diagnosis in swine. An animal was placed on the pen's floor in the lying position, with out being restrained or anesthetized. The transducer was applied gently to the skin of the lower abdomen or the flank. Ultrasonic Doppler signals based on the fetal circulation were heard by the operator's ears and at the same time, recorded on magnetic tapes for the convenience of fetal heart rate caculation. The maternal circulation was distinguished easily from the fetal one for its markedly slow rhythm. Accuracy of pregnancy diagnosis was based on delivery.
A total of 83 experiments were carried out on 70 sows of 4 different breeds over a period from 22 days post-coitum to the full term. The accuracy rate for pregnancy diagnosis was not satisfactory (58.3%) 30 days or more post-coitum, but became high between 30 to 39 days (81.8%). It reached 100% after 40 days of pregancy. Pregnancy could be detected by this method as early as 26 days postcoitum.
A highly significant negative correlation was observed between fetal heart rate and fetal age. The orrelation coefficient was -0.87 (P <0.01). The fetal heart rate became low in a negative linear regression as gestation progressed:
Y=252.6-0.572X (X=fetalage, Y=fetal heart rate).