Changes in the Fetal Heart Rate of Thoroughbred Horse through the Gestation

Abstract

Fifty-nine recordings of fetal and maternal heart rate (FHR and MHR) were made from 10 pregnant Thoroughbred mares. Each recording lasted for an average of 20 min. The heart rate was calculated at an interval of 10 sec from beat to beat using the R or S wave of the fetal electrocardiograms as the indicator of each heart-beat. FHR was classified into the baseline FHR and the FHR acceleration, the latter of which was a brief tachycardia occasionally observed. The baseline FHR decreased logarithmically with the advance in gestational period, while the mean MHR increased. The frequency and the magnitude of the FHR acceleration increased at the later period of gestation, suggesting the development of fetal body movements.