Reference values for fetal heart rate in cattle in the first trimester of pregnancy

The aim of this study was to create a fetal heart rate (FHR) reference curve for singleton bovine fetuses in the first trimester of gestation and to determine its possible relationship with the outcome of pregnancy. Forty-eight Holstein-Friesian cows with one fetus and five cows with twins were used. Fetal heart beatings were recorded on videotape during transrectal scanning with a 5 and/or 7.5 MHz linear array transducer on a weekly basis between Days 40 and 95 of gestation. FHR was calculated by averaging the results of five counts of the same record by the same observer. For singleton pregnancies, a reference curve was created using the mean, the standard deviation (SD) and the 5th and 95th percentiles. The FHR increased from Days 40-46 (173 beats/min) to Days 61-67 (183 beats/min). After a peak, the FHR decreased slowly until Days 89-95 (175 beats/min), while the SD increased. There was no significant difference between singleton and twin fetuses. in the aborted and lost fetuses in twin gestation due to fetal reduction, both bradycardia and tachycardia were detected compared to the singleton pregnancy reference curve.