Ultrasonographic monitoring of 103 recipient mares of different reproductive status during the first 30 days after embryo transfers

Determination of the genital tubercle migration period in Morada Nova sheep foetuses by ultrasonography

The aim of this study was to determine the period of genital tubercle (GT) migration using ultrasonography in Morada Nova sheep foetuses (n = 117) from natural mating (NM) and frozen embryo transfer (ET) to determine the window when foetal sexing can be determined. The examinations were performed using transrectal ultrasonography with a dual-frequency linear transducer (6.0 and 8.0 MHz) from day 30-54 of pregnancy at 48-h intervals. The period of GT migration of foetuses produced by NM varied from 36 to 46 days of pregnancy, resulting in an average of 39.5 +/- 2.9 days. For foetuses derived from ET, GT migration varied from 42 to 52 days of pregnancy with an average of 48.5 +/- 3.3 days, being possible the GT of foetuses from ET start to migrate 96 h later even if they are of the same gender. Migration of the GT occurred earlier (p < 0.05) in foetuses produced by NM and sexing accuracy for triplet pregnancies (77.8%) was significantly inferior (p < 0.05) to single (100%) and twin (92.9%) pregnancies for foetuses derived by NM. The results allow one to conclude that foetal sexing can be done from the 50th day onwards in foetuses produced by NM and from the 55th day onwards in foetuses derived from ET, and that multiple pregnancies compromise the sexing accuracy by ultrasonography.

Sexing of Dorper sheep fetuses derived from natural mating and embryo transfer by ultrasonography

In order to improve fetal sexing in the Dorper sheep breed, the objective of the present study was to determine, by repeated ultrasonographic examinations, the migration period of the genital tubercle (GT) in sheep fetuses derived from natural mating or embryo transfer and to compare the accuracy of a single examination with repeated examinations at short intervals. For this purpose, transrectal ultrasound was performed, using a double-frequency linear transducer (6.0 and 8.0 MHz) for monitoring 51 sheep fetuses distributed in three experimental groups (EI, EII and EIII). The fetuses in EI (n = 23) and EII (n = 18) derived, respectively, from natural mating and embryo transfer were monitored at 48-h intervals from the 30th to 60th day of gestation and sexed based on the final location of the GT. The fetuses in EIII (n = 10), which originated from embryo transfer, were examined only once on the 65th day of gestation and sexed taking into consideration the final position of the GT and/or by identification of anatomical structures of external genitalia. The accuracy of fetal sexing was 91.3% (21 fetuses sexed/23 quantified) in EI, 88.9% (16 sexed/18 quantified) in EII and 100% (10 sexed/10 quantified) in EIII, without significant difference (P > 0.05) between experiments. Migration of the GT occurred earlier (P < 0.05) in fetuses produced by natural mating (43.0 +/- 2.8 days) than in those derived from embryo transfer (46.1 +/- 4.7 days). The results show that fetal sexing can be done from the 50th day onward in fetuses produced by natural mating and from the 60th day onward in fetuses derived from frozen embryos. It can also be concluded that repeated ultrasonographic exams in short time intervals do not maximise the accuracy of fetal sexing. In addition, real-time ultrasonography is a reliable tool for fetal sex determination in sheep after Day 50 of gestation, taking into account both the location of the GT and the identification of external genital structures.