Application of B-ultrasound in the diagnosis of pregnancy in dogs

The use of ultrasound in veterinary medicine began in the mid-1960s with the introduction of type A and D ultrasound. With the development of electronic technology and electronic industry, it developed into M type and B type in the mid-1970s. B-mode ultrasonic diagnostic instrument, also known as B-mode ultrasound, uses photometric modulation type, reflecting the strength of the signal by the brightness and darkness of the light spot. Because the application of B ultrasound to the body for timely imaging, showing the two-dimensional image of the examined part, clearly showing the dynamic changes of the internal organs and tissues of the body, shape and adjacent relationship, as well as the internal echo of soft tissue, structure, distribution of blood vessels and other channels, B ultrasound is also known as timely ultrasonic tomography diagnostic instrument. Because B-ultrasound has no damage to the body, it can also be processed under its supervision, and it has a wide range of applications, so it has been paid attention to and widely used in the medical field as soon as it is published, and has now become one of the four medical imaging diagnostic methods. In veterinary and livestock production, B ultrasound has also been widely used; at present, whether in foreign or domestic, whether in veterinary basic theoretical research, or in animal production practice and veterinary clinical application, B ultrasound plays a very important role, known as a revolutionary change in veterinary diagnostic technology, is applied to pregnancy monitoring, superovulation, disease diagnosis and breeding and fattening monitoring and other fields. At present, one of the main uses of B ultrasound is to monitor the uterus and fetus of animals during pregnancy. Combined with the author's experience, this paper briefly describes the main applications of B ultrasound in dog pregnancy monitoring.

1 Early pregnancy diagnosis

Early pregnancy diagnosis by B-mode ultrasound can directly display embryo sac and embryo on screen with high accuracy. Depending on the breed and individual of the dog, the gestation period is 58 to 65 days, usually 62 days. Implantation begins 15 - 18 days after fertilization; gestational sac can be detected by B-ultrasound about 20 days after fertilization, but GS can be detected as early as 15 days. The early pregnancy of dogs was judged by B ultrasound mainly according to the GS (diameter 1~2cm) in the round liquid dark area observed in the uterine area of ultrasound section, the enlargement of uterine horn section and the thickening of uterine wall. The method of exploration is to cut the hair on the abdominal wall or both sides, and then use 5 or 7. 5MHz linear array or fan scan probe to observe the horizontal, longitudinal and oblique scanning sections. When one or more GS dark areas are found, pregnancy can be judged. However, it should also be distinguished from the intestinal tract or uterine effusion. GS is defined as circular liquid dark area with thick wall and strong echo in transverse section and longitudinal section, and luminal effusion is defined as circular liquid dark area with thin wall in longitudinal section. The positive rate of early pregnancy in dogs can reach 100% for skilled operators, but the negative judgment of early pregnancy in dogs should be cautious, because the uterine horn of dogs is very thin (generally less than 1cm in diameter) before pregnancy and 20 days before pregnancy, and almost no lumen can be seen, so it is difficult to detect by B ultrasound. When suspected early pregnancy negative, should be in 23~25 days or even more after the gestation period repeated careful review, pregnant with few offspring more likely to appear early pregnancy negative judgment error.

2 Monitor ovarian development for proper mating

The ovaries of dogs are very small, generally 1.5~3×0.7~1.5×0.5~0.75cm, and the outer envelope and fat are easy to produce echo interference, so it is necessary to find the correct position and observe carefully when exploring. The ovary is mulberry-shaped, located below the 3rd or 4th lumbar vertebra, 1~4cm behind the kidney, and more backward and downward in postpartum dogs. Ovary with developing follicles can be observed in B ultrasound section 2~3 days after estrus; ovarian capsule with thin outer fat can be clearly seen, outer echo under capsule is weak, and there is pattern strong echo in central area; follicles present multiple circular echo areas in periphery, and the maximum diameter can reach 13 mm. Follicles grow slowly in the first to second oestrus (about 8 days after oestrus), and grow rapidly in the third oestrus (about 10 to 15 days after oestrus), and then stop growing. At this time, ovulation is about to occur, which is the best period for mating or artificial insemination. When monitoring ovarian development by B ultrasound, the number of mature follicles (more than 3mm in diameter and protruding from the envelope) can be calculated from multiple sections. When the number of mature follicles is too few (less than 5) or the number of follicles growing synchronously is small and slow, appropriate gonadotropin (such as FSH or PMFfGLH or HCG) can be used to promote ovarian development and ovulation, improve conception rate and increase litter size.

3. Monitoring of embryo development, number of pregnant fetuses, gestational age and stillbirth

In pregnancy monitoring, prediction of fetal number is important for feeding management. In the third trimester of pregnancy, maternal nutrition is directly related to fetal birth weight. According to the number of pregnant animals were divided into different groups, and the corresponding feeding plan was formulated, which could reduce the feeding cost, ensure the normal development and postnatal growth of puppies, and avoid fetal asphyxia and pregnancy toxemia caused by improper feeding.

B ultrasound can be used to observe the external structure of the embryo (such as uterus, gestational sac, placenta, fetal membrane and umbilical cord), the shape of the embryo (such as fetal outline, limbs, external genitals and fetal movement), and the internal structure of the embryo (such as fetal heartbeat, internal organs and bones). The gestation sac was observed in 15~20 days after pregnancy, the embryo body (bright mass with strong echo appeared in the chorionic sac) was observed in 23~25 days, the fetal heart beat was observed in 21~28 days, the head and trunk could be distinguished in 26~28 days, the limbs and choroid plexus could be distinguished in 31~35 days, ossification began in 35~40 days, and the optic vesicles and internal organs could be distinguished in 40~47 days. At about 23 days, the number of embryos can be estimated according to the number of GS and embryos; the fetal age can be predicted according to the echo structure that can be recognized by B ultrasound section; and the stillbirth, emphysema, embryo absorption and abortion can be distinguished according to the fetal heartbeat and embryo structure. According to the internal structure of uterus during and after delivery, monitor delivery, judge whether delivery is over, monitor postpartum uterine reinstatement, etc.

4 Diagnosis of reproductive diseases

The common reproductive diseases of dogs are pyometra and hydrops, ovarian cyst, dystocia and abortion, tumors of uterus, breast and testis, and prostatic hypertrophy and tumor, etc., which can be diagnosed or differentiated by B ultrasound, and the position, size and character of pathological tissues can be analyzed qualitatively and quantitatively. If there is a black uniform weak echo area in the uterine horn, it indicates that the uterine horn contains a large amount of liquid; if the liquid contains a similar thick substance, it indicates that the uterus is empyema.