Veterinary B-ultrasound machine in dairy cow embryology ultrasound imaging and *** application

Veterinary B-ultrasound machine can be used to estimate gestational age, monitor fetal growth and diagnose pregnancy disorders. All parts of the fetus such as eyeballs, stomach, ribs, etc. can be detected. In order to determine the development of each organ, the probe position should be adjusted to obtain the largest scanning section. The growth correlation coefficient of each tissue can also be calculated according to the gestational age. In short, the gestational age and growth and development degree can be determined according to the size of each organ of the fetus. At the same time, an ultrasound imaging system for changes in dairy cow fetuses can be established, and the birth date can be accurately predicted based on this to facilitate production management. Generally, in production, the rectal detection of the number of gestational fetuses and the identification of sex of dairy cows are carried out simultaneously with the veterinary B-ultrasound machine. The appropriate time range is 55 to 75 days after pregnancy, usually measured at 67 days. It is not suitable for *** if the pregnancy time is too long or too short.

Insemination is mainly determined by locating the reproductive nodules related to the tail and umbilical cord. Specifically, if the umbilical cord is imaged as a bright spot, and there is another bright spot near the umbilical cord, that is, the abdomen of the fetus, and there are no two or three bright spots at the base of the tail, it can be judged as a male; if there is only one bright spot of the umbilical cord in the abdomen, and there are two or three bright spots at the base of the tail, it can be judged as a female.

After completing the identification of one fetus, the work is not over yet. The above method should be used to detect whether there are other fetuses and identify their gender. A large number of production practices have proved that except for very few special cases, such as the fetus in the cow's pregnancy is not in a good position, it is deep, and the cow is too hard, so that the hand-held probe cannot be imaged clearly, resulting in insemination failure, other situations can be detected as long as the correct method is carefully operated. For specific usage methods, please refer to the problems and solutions in the operation of the B-ultrasound machine for cattle

Early insemination method of dairy cows

(I) Cytogenetic method

Embryo insemination is completed by karyotype analysis, which was first used in rabbits, sheep, and cattle. First, a small amount of embryonic cells are taken and cultured in a culture medium containing colchicine. Due to the inhibitory effect of colchicine, the mitosis of the cells is stopped in the metaphase. Under the action of osmotic pressure, the cells swell, the cell walls rupture, and the chromosomes are released. Then, after fixation and Giemsa staining, they are observed under a microscope. Since mitosis is blocked in the metaphase, the chromosomes are shortened, regular in shape, and have a specific banding pattern. Through karyotype analysis, it is determined whether the sex chromosome type is XX or XY. This method is almost 100% accurate in identifying the sex of the embryo, but the operation process is relatively cumbersome.

(II) X chromosome ligase activity assay

The type of mammalian sex chromosomes is XX for females and XY for males. In order to maintain the genetic balance between sexes, in the early stages of embryonic development, one x chromosome in each cell of a female individual is inactivated. Although the exact time of the inactivation of this x chromosome is still unknown, it is certain that there was a period of time before the inactivation of this chromosome when both X chromosomes were active and transcribed. This is reflected in the fact that in the early stages of embryonic development, the activity of the x chromosome ligase in female embryos is twice that of male embryos. Based on this fact, Williams and Monk et al. detected the activity of X-chromosome linked enzymes, namely glucose-6-phosphate dehydrogenase, during the period from mouse morula to blastocyst stage to predict the sex of embryos. The results of delivery after transplantation showed that the accuracy rates of female and male embryos were 72% and 57%, respectively. The accuracy rate of embryo identification by this method is low, mainly because the exact time of X chromosome inactivation is unknown.

(III) H-Y antigen method

There are currently two methods for embryo identification using H-y antigen, namely cytotoxicity analysis and indirect immunofluorescence.

1. Cytotoxicity analysis method

The embryos are cultured in a culture medium containing H-Y antiserum and complement (guinea pig serum). Embryos with H-Y antigen show a certain degree of cell lysis, and such embryos are judged as male embryos. After the embryos that can continue to develop, that is, H-Y negative embryos are transplanted, 86% of the offspring are female. This method is at the cost of destroying male embryos, so it is rarely used now.

2. Indirect immunofluorescence method

First, the embryos from the 8-cell to blastocyst stage are reacted with H-y antibody for 30 minutes, and then reacted with immunoglobulin M (IgM) antibody labeled with fluorescein isothiocyanate (FITC). Then the embryos are checked under a fluorescence microscope to see if they have fluorescein. If they do, they are judged as male. The main advantage of this method is that it does not damage the embryo and has a relatively high accuracy rate. The accuracy rates for female identification of pigs, sheep, and cattle can reach 81%, 85%, and 89%, respectively. However, this method requires a fluorescence microscope and rich experience.

(IV) Y chromosome-specific DNA probe method

The application of this method requires a complex technical process to prepare a specific, isotope-labeled probe of the Y chromosome-specific sequence. This probe is used to hybridize with a small amount of DNA extracted from embryonic cells. A positive hybridization result indicates the presence of a Y chromosome and can be judged as male. The accuracy of this method is 90%.

In the early 1990s, British scholars discovered a DNA fragment that determines maleness on the short arm of the Y chromosome and named it SRY, the sex-determining region (gene). This discovery is considered one of the major achievements of biological science since the 1990s, and it has laid the foundation for further research on sex control. Combining it with polymerase chain reaction (PCR) amplification technology and applying it to embryo fertilization, the accuracy rate can reach 100%; domestic researchers have successfully used PCR technology to directly amplify the SRY-specific DNA sequence of bovine embryos, which can accurately identify the sex of bovine embryos.

With the advancement of science and technology, fast and effective methods are the future development trend. Veterinary B-ultrasound machines have obvious advantages in dairy cow fertilization methods, so they are also the main detection tools for the future dairy industry.

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