What is embryo transfer in dairy cows?

Embryo transplantation refers to taking out the early embryos from a well-bred cow and transplanting them into another cow of the same species with the same or similar physiological status, so that it can continue to develop into a new individual. Therefore, Also called borrowed belly pregnancy. The individual who provides the embryo is called the donor, and the individual who receives the embryo is called the recipient. The genetic material of the offspring produced by embryo transfer comes from the donor cow and the bull that mates with it, and the nutrients required for development are obtained from the recipient. Therefore, the donor determines its genetic characteristics (genotype), and the recipient only affects its offspring. Physical development. Embryo transplantation generally uses well-bred cows as donors and individuals with poor production performance as recipients to maximize the number of well-bred offspring through a "borrowed pregnancy" method.

Embryo transfer can improve the reproductive rate of excellent female animals and unleash the genetic potential of excellent breeds. The donor cow for embryo transfer only provides fertilized eggs, thus saving the long time required for pregnancy. Generally, the donor cow can use superovulation technology to release several eggs each time, that is, it can produce several offspring each time. Embryo transfer can induce a cow to give birth to twin calves. Embryo transfer can be used to allow fetal development in both sides of the uterus of the recipient cow, but this technology is mostly used in beef cattle and mutton sheep and is not recommended in dairy cows. Embryo transfer can meet the needs of preserving breed resources and developing in different places. The embryos removed from the donor can be stored for a long time through freezing, so that the characteristics of excellent female animals can be slowly and long-term continued, and it can also replace the introduction and off-site development of breeding animals. Embryo transplantation can overcome the defects of infertility and miscarriage of excellent breeding cows, so that the fertilized eggs can be used to calve. Through embryo transplantation, local cheap cattle, hybrid cattle and cattle with low milk production potential can be used to produce excellent breeding cows. .

The key measure for embryo transfer is the consistency of donor and recipient. That is, only when the reproductive environment of the recipient cow is completely consistent with the environment when the imported embryo was collected can the embryo develop normally. Moreover, it is necessary to ensure that the collection and transplantation of embryos are carried out several days before the cyclic luteal regression of the female animal, so that the embryos can survive after transplantation. The process of embryo transplantation: select the recipient cow as preparation; prepare the recipient cow and the donor cow for estrus at the same time; superovulate the donor cow; artificial inseminate the donor cow 2 to 3 times with an interval of 8 to 10 hours; 4 to 8 hours after mating, the embryos are flushed out of the reproductive tract using special flushing fluid; the embryos are inspected, stored and cultured for a short period of time; and then transplanted to the recipient cow.

There are some difficulties in the application of embryo transfer: due to individual differences in cows, the number of ovulations in recipients after hormone treatment varies greatly; the flushing and collection rate of fertilized eggs (embryos) is low (50% ~80%), generally the more embryos there are, the more difficult it is to collect; the success rate of transplantation is low (generally around 60%), and each healthy calf requires 4 to 5 embryos.