Generally, the fetal sac of a female dog can be detected by veterinary B-ultrasound about 20 days after mating. The veterinary B-ultrasound diagnosis of early pregnancy in a female dog is mainly based on the observation of circular liquid dark areas in the uterine area of the ultrasound section image, enlarged uterine horn section, thickened uterine wall and other indicators. The embryo and fetal heartbeat can be seen after 25 days of pregnancy.

The female dog can be restrained naturally standing or lying down, and it is best to restrain the female dog in a supine position. The veterinary B-ultrasound exploration site is from the rear ribs to the entrance of the pelvic cavity, the edge of the breast (about 2 cm outside the nipple from the back of the uterus), and the exploration is carried out along the midline of the abdomen to the dorsal side. Except for short-haired dogs, the hair is partially cut, and the coupling agent is evenly applied to the veterinary B-ultrasound probe. Linear array scanning is performed. When scanning horizontally, the probe moves left and right with the midline of the abdomen as the axis; when scanning longitudinally, the probe is parallel to the front edge of the pubic bone to explore the thickness and volume of the uterine wall, as well as the echo of the fluid in the uterine cavity.

The image orientation is determined according to the direction of the veterinary B-ultrasound probe during the exploration, that is, the image of the front of the probe is on the right side of the fluorescent screen, and the image of the back is on the left side of the fluorescent screen. The direction can also be adjusted according to one's own preferences. The tissue close to the veterinary B-ultrasound probe is in the upper part of the image, and the tissue far from the probe is in the lower part of the image. The upper and lower images of the veterinary B-ultrasound can also be adjusted.

Veterinary B-ultrasound can be used to observe the development process of the embryo, the growth of the fetus, the fetal heart rate, and the development process of the trunk and limbs, etc., but it has a lot to do with the operator's proficiency and the mastery of anatomical knowledge. The fetal sac can be seen in the female dog at about 20 days of pregnancy, the fetal body can be seen at 25 days, the fetal heart beat can be seen at about 28 days, the head and trunk can be distinguished at 30 days, the limb buds can be distinguished at 35 days, and ossification begins at 40 days

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