Transrectal ultrasound evaluation of mule conceptus and feto-placenta unit

The objective of the present study was to describe the ultrasonographic evaluation of the mule embryo during gestation. Six multiparous trotter were assigned to the experiment and were subjected to daily ultrasound monitoring of the ovarian activity until artificial insemination with donkey stallion fresh semen. Upon day 8 post ovulation the animals were examined for early pregnancy diagnosis and the following biometries were recorded: uterine horn and embryonic vesicles (EV) diameter, EV localization, day of fixation and change in shape. ALl the mares conceived and 11 EV were observed. First day of pregnancy was established on day 8 post ovulation in 37% of the mares, with a mean diameter of 4.6+1.3 mm. EV fixation occurred in the left corpo-cornual junction at day 17.3+1.3, in 77.78% of the mares, with a mean diameter of 25+1.5 mm. Proper embryo was first observed at day 19.8+2.7, with a mean diameter of 2.3+1.0 mm. Embryonic cardiac activity was first observed at day 24+2.7 post ovulation. Allantoic sac emergency occurred at day 23.3+1.9 and its formation was completed at day 34+3.4. From the first trimester of gestation to parturition, feto-placental unit (UFP), were recorded, each by transrectal and transabdominal approaches. Mule EV is detected more precociously compared to both donkey and equine EV. Nine gestations (82%) proceeded to delivery with an average length of 349.2+2.6 days.