Veterinary B-ultrasound observation of fetal bones in dogs, the skull reflex is first observed during the period of 31-35 days of pregnancy, which is a strong reflex band consistent with the inherent shape of the head. As the fetal cranial cavity and eye sockets form and calcify with the bones, the shape on the veterinary B-ultrasound image becomes clearer and clearer, showing an echo halo from weak to strong, forming a relatively obvious skull acoustic shadow. Then the image reflections of the spine ribs and limb bones can be seen. At 36-38 days of pregnancy, the overall bone outline of the fetus can be basically observed through veterinary B-ultrasound.

Veterinary B-ultrasound observation of fetal viscera in dogs, at 31-35 days, the fetal direction can be identified based on the skull reflex and the image echo of other bones, and the position of the heart, stomach and bladder can be determined by the fetal direction and heart beat. Around 36 days of pregnancy, in the front part of the fetal abdomen, veterinary B-ultrasound can observe an elliptical dark area, which is a stomach filled with fluid. An elliptical dark area slightly smaller than the stomach can be observed in the posterior part of the fetal abdominal cavity, which is a bladder with urine accumulation. At around 38 days of pregnancy, veterinary B-ultrasound can observe the oval kidneys of the fetus on the back of the fetus, and the echo reflection is weaker than that of the surrounding tissues. When the fetus develops to 39-43 days, there are also some weak echoes relative to the liver and lungs. Similar to the kidney echoes seen previously. At 43 days, the eyes and mouth of the fetus can be distinguished. It is not until a period of time near delivery that the intestines in the fetal abdominal cavity can be seen through veterinary B-ultrasound.

Veterinary B-ultrasound observes the fetal heart and fetal movement. Heart beats and fetal movement are signs of fetal activity. As the pregnancy time prolongs, at 26-28 days after mating, the embryonic sac and embryo body gradually increase in size. Regular and fast flashing light spots can be observed in the embryo body, which are small echo areas with embryo beats, that is, the reaction of the heart structure and heart beats. After 40 days of pregnancy, due to the increase in the fetal body, the veterinary B-ultrasound probe can scan the heart beats in the fetal chest cavity, and at the same time, relatively obvious fetal movements can be observed. The swing of the fetal limbs can be observed at 35 days of pregnancy, and the shaking of the fetal head and neck can be observed at 49 days of pregnancy. The fetus' heart rate is about twice that of the mother dog.

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