274 USE OF DOPPLER ULTRASOUND FOR EQUINE FETAL SEX DETERMINATION

Abstract

Fetal sex determination in horses is increasingly practiced because of commercial interests, such as obtaining offspring of a desired sex. However, in the last several years, the sex determination technique has been done exclusively by genital tubercle evaluation (55 to 70 days of pregnancy), and it has begun to be done more frequently in horses through evaluation of the fetal gonad (100 to 160 days of pregnancy) because of the difficulties of finding the genital tubercle and the large size of the fetal gonad around 4 months of pregnancy. Doppler ultrasound constitutes a practical, effective, and non-invasive technique for real-time blood flow evaluation of the reproductive tract in horses. The aim of this work was to compare two methods of ultrasound to diagnose equine fetal sex between 100 and 140 days and between 140 and 160 days. Evaluations were performed in 112 pregnant mares between 100 and 160 days of pregnancy using B-mode and colour Doppler ultrasound (My Laboratory Five^®, Esaote, Nutricell, Campinas, São Paulo) transrectally. The accuracy of sex identification by ultrasound was successfully tested after birth in all the fetuses analysed (44 females and 68 males). By B-mode ultrasound, it was possible to visualise the gonad in all fetuses (44/44) of females between 100 and 160 days of pregnancy. In males, during the period of 100 to 140 days of pregnancy, gonads and mediastinum were observed in all male fetuses (48/48) of evaluations, and between 141 and 160 days of pregnancy, gonads were detected in 100% (20/20) of fetuses and the mediastinum was detected in 30% (6/20). With colour Doppler ultrasound, the vascularization of the female gonad (between the cortical and medullary zones) was observed in 100% (44/44) of females. In males, between 100 and 120 days of pregnancy, the vascularization of the pampiniform plexus and testicular vein were observed in 100% (28/28) of cases. During the period between 121 and 140 days, vascularization of the pampiniform plexus was observed in 100% (20/20) of the fetuses, and vascularization of the testicular vein was observed in 90% (18/20). When evaluated between 141 and 160 days of pregnancy, vascularization of the pampiniform plexus was detected in 100% (20/29) of male fetuses and vascularization of the testicular vein was detected in 80% (8/10). There was no statistical difference between results obtained with B-mode and colour Doppler ultrasound. Both techniques had high accuracy for equine fetal sex determination. However, according to information from the operators, the colour Doppler ultrasound allowed for a faster and more practical exam because visualisation of tissue blood perfusion facilitated the anatomical assessment of fetal structures. In summary, colour Doppler ultrasound is an effective technique for equine fetal sex determination between 100 and 160 days of pregnancy.