RESUMEN
The aim of the present study was to identify the migration period of the genital tubercle and its later differentiation into external genital structures in fetuses derived from natural mating and fetuses from fresh, frozen and vitrified embryo transfer. A transrectal ultrasound with a double-frequency linear transducer (6.0 and 8.0 MHz) was used to monitor 123 goat fetuses, which were allocated to one of four groups: fetuses originating from controlled natural mating (G1, n = 32) and fetuses derived from fresh (G2, n = 34), frozen (G3, n = 30) and vitrified (G4, n = 27) embryo transfer. The transferable embryos were collected 7 days after mating by laparoscopy. Migration of the genital tubercle occurred significantly earlier (P < 0.05) in G1 than in G2, G3 and G4. The visualisation of the scrotum, prepuce and vulva occurred significantly earlier (P < 0.05) in G1 than in G2, G3 and G4. Our results show that fetal sexing is feasible after 55 days for fetuses from natural mating and after 60 days in fetuses from fresh and cryopreserved embryos. Thus, real-time ultrasonography is a reliable tool for fetal sex determination in goats after Day 50 of pregnancy, taking into account both the location of the genital tubercle and the identification of external genital structures.