The early embryo detection of small-tailed Han sheep by B-ultrasound of sheep, the earliest time to detect the embryo by B-ultrasound of sheep varies with the sheep species, whether it is parous, the frequency of B-ultrasound probe of sheep and the method of detection. The time to detect the early embryo by transrectal detection of 7.5MHz B-ultrasound probe of sheep is basically about 20 days. Moreover, this is the earliest time to detect the embryo in the relevant literature, indicating that the size of the embryo reaches or exceeds the resolution of the 7.5MHz B-ultrasound probe of sheep at 18-19 days of pregnancy. Whether the use of higher frequency B-ultrasound probe of sheep can advance the earliest time to detect the embryo, still needs further study.

In the examination of B-ultrasound of sheep, the fetal movement has experienced a process of slow-fast-slow, local-whole-local, from mild to violent, from simple to complex. Studies in recent years have shown that fetal movement is related to the development of the control mechanism of the central nervous system. Different types of fetal movement reflect the development and maturity of different central nervous systems. Therefore, the change of fetal movement marks the development progress of fetal nerves and muscles, and reflects the function of the central nervous system. Fetal movement is a symbol of the life structure of the fetus and a sign of health.

The amniotic sac of sheep is formed at about 13-16 days of pregnancy. Only when the amount of amniotic fluid in the amniotic sac accumulates to a certain extent can it be monitored by Sheep B-ultrasound. Because the amniotic membrane is very thin, it is difficult to display it with sheep B-ultrasound, so the complete amniotic structure of the amniotic sac cannot be seen. Only part of the amniotic membrane can be seen, but this is enough to measure the diameter of the amniotic sac. The diameter of the gestational sac (chorionic sac) is often used as a parameter in the identification of the gestational age of human fetuses. However, due to the uterine structure and fetal membrane characteristics of the Small Tail Han sheep, it is more reasonable to use the diameter of the amniotic sac to identify the gestational age in the early pregnancy. However, its accuracy still needs to be verified.