Prediction of Gestational Age in Warmblood, Standardbred and Thoroughbred Horses Based on the Table Established in Light Breed Horses Using Foetal Ultrasonographic Measurements of Four Biometric Parameters.

Using the equation of Hartwig et al. and the table established for light breed horses, day of gestation was predicted in 108 Warmblood (WB) and 59 racehorses (Thoroughbred [TB] and Standardbred [STB]) pregnant mares. In WB, gestational ages were predicted within 2 weeks from 100 to 200 days of gestation using biparietal diameter (BPD), aortic diameter (AortD) or femur length (FL); within 2 weeks from 100 to 250 days using BPD or AortD; within 2 weeks from 100 to 300 days using BPD alone; and within 3 weeks from 100 to 350 days using eye approximated volume (EyV) alone. In the racehorse group, gestational ages were predicted within 2 weeks from 100 to 200 days of gestation using BPD or AortD; within 3 weeks from 100 to 250 days of gestation using BPD or FL; and within 3 weeks after 300 days of gestation using EyV. Across breeds including Quarter Horses (QH), WB, STB and TB, BPD was the best foetal age predictor from 100 to 200 days of gestation and from 200 to 300 days of gestation with accuracies within 2 and 3 weeks, respectively. After 300 days of gestation, EyV was found to be the best predictor with an accuracy of within 3 weeks. Overall, in the two groups, the breed of the foal nor the breed of the dam (except for short days increments), had any effect on foetal age prediction. Therefore, the table established for light breed horses can be used to assess the foetal age of foetuses carried by recipient mares whether they are WB or STB. Using the same anatomical landmarks but a different ultrasound machine, both ultrasonographers determined foetal age with similar accuracy.