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Embryo transfer

Transfer of bubaline embryos may be done either surgically or non-surgically. In cattle the surgical approach seems to produce the most consistent results. Successful non-surgical transfer requires an even higher degree of dexterity and skill than does the surgical embryo recovery procedure.

Surgical exposure of a uterine horn needs to be done via a mid-line incision if the recipient is a heifer with a short broad ligament or if it is to receive twin embryos (one in each uterine horn). Halothane anaesthesia provides excellent relaxation of the broad ligament. Single transfers are always made to the horn ipsilateral to the corpus luteum. Two embryos should be transferred to separate horns as uterine migration of embryos rarely, if ever, occurs in the female bovine. The uterine horn is exteriorized by placing tension on the broad ligament over the distal portion of the horn, and not by directly pulling on the horn itself. In pluriparous animals, the incision may be made in the flank on the side of the corpus luteum as far caudally as possible with the animal in the standing position.

With both approaches a small stab incision is made along the greater curvature about 7 cm from the tip of the exteriorized uterine horn with a small, closed mosquito forceps. The instrument characteristically “pops” through the endometrium. Care should be taken not to pass through the lumen into the endometrium and submucosa on the other side. The embryo is deposited in the lumen of the uterus via the stab incision with a fine, modified Pasteur pipette. Closure of the abdominal incision following either approach is by routine surgical methods.

Non-surgical transfers are made through the cervix as for artificial insemination. It is important to minimize contamination of the uterus because it is more susceptible to infection during the luteal phase. Faeces are evacuated from the rectum and the side of the corpus luteum is determined. Epidural anaesthesia is induced to prevent defaecation and to minimize straining. The perineal region is thoroughly washed and the vulva is blotted dry.

In the laboratory the embryo is aspirated into a 0.25-ml French straw between two air pockets and two columns of culture medium. The straw is inserted into the AI gun and shortened level with the end of the gun. A sterilized sheath is fitted over the AI gun and fixed in place (Figure 10). A second, sterile, larger (sanitary) sheath which is closed at the distal end is fitted over the first to serve as a cannula to permit passage of the gun through the vagina without coming into contact with the vaginal flora. The tip is placed into the external os of the cervix and is then pushed through the sheath before it is guided as gently as possible through the remainder of the cervical canal and into the uterine horn on the side of the corpus luteum. The embryo is then gently deposited approximately one-third of the way up the uterine horn (Figure 11) and the gun is withdrawn slowly. A negative correlation has been demonstrated between the time spent manipulating the cervix and the uterine horn and the pregnancy rate. Success is related to dexterity and practice. Pregnancy rates achieved by most operators improve with experience. The pregnancy rate in cows after non-surgical transfer through the cervix is generally 10–15 percent lower than that reported after surgical transfer. In the hands of some experienced embryo transfer practitioners, pregnancy rates following non-surgical transfer approximate those after surgical methods.

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