Ref Code: CAT18

Category

Teaching - 3 (Instructor : student ratio 1:3)

Research - 4

Objective

To collect embryos from the reproductive tract of the donor(s) and transfer these to the reproductive tract of the recipient(s) so that a viable pregnancy may be established. Alternatively, the embryos may be frozen and stored for use at a later date.

Alternatives to animal use for teaching

Students can be given preliminary instruction with visual aids, and the manipulation of the tract and placement of collection catheters and transfer pipettes can be done on abattoir material to aid in training, but the procedure must be practised with live animals to attain proficiency.

Details of procedure

The processes of collection of embryos from the donors and transfer to recipients is generally referred to as embryo transfer (ET), without restriction to the transfer procedure only. The total operation of ET also often involves the technology of freezing and thawing of embryos, for which there is a large body of published techniques. Embryos may be transferred shortly after collection (fresh transfer), held cooled for a short period (a few hours or overnight) or frozen after collection for thawing and transfer at a later date.

Collection of embryos from donors can be done by surgical techniques, but most operators now use non-surgical (trans-vaginal) collection procedures. All techniques are based on the placement of catheters into the lumen of the horns or body of the uterus and flushing out the embryos with specifically designed media into collection apparatus. Differences in currently used techniques are mainly in the type of catheters used.

The donor is contained in a crush, usually with head-bail restraint. The usual practice is to use an epidural anaesthetic (see below) for relaxation of the rectum and local effect on the tract to aid manipulation. The collection catheter is passed through the cervix and located in place, usually in each of the uterine horns in succession, by manipulation with a hand inserted in the rectum (similar to the manipulation of the cervix during AI).

When the catheter is correctly located, the cuff is inflated and flushing medium passed through to collect the embryos. The embryos are located and retrieved from the flushed fluid using a microscope, assessed for quality on appearance and stage of development, and then either prepared for transfer, or frozen for storage.

Drugs, chemicals or biological agents

Drugs associated with synchrony of oestrus will be required for these procedures (see SOP 26). Drugs to induce superovulation are generally preparations of pituitary extracts (of various species, mostly porcine or bovine), with the active agent being FSH, but the originally used preparations of PMSG can still be used. Additionally, a local epidural anaesthetic (commonly, 5-10 mL of 2% lignocaine hydrochloride, injected between first and second coccygeal vertebrae) is used for both donors and recipients.

Impact of procedure on the wellbeing of animal(s)

The procedures have minimal impact on either donor or recipient cattle. However, donor animals are required to be restrained for some time during collection of embryos, and those with a poor temperament may need particular attention if they are not able to be left out of the program.

Reuse and repeated use

The main issue with repeated treatments is that of the response in recoverable embryos, since there do not appear to be any adverse effects on the animals provided the procedures are done by competent operators. Published work has shown satisfactory results with up to 10 repeat superovulation treatments. This frequency is unlikely to be reached in programs currently used, and the more common practice of 1-4 collections in a season should present no problems.

Care of animal(s) during/after procedure

Normal observation and attention to animals’ reactions to restraint are necessary during collection and transfer. No reactions after the procedures would be expected.

Pain relief measures

Non surgical procedures are not perceived to cause pain and thus relief measures are not generally applicable. The use of the epidural anaesthetic is of primary benefit for ease of manipulation of the tract.

Qualifications, experience or training necessary to perform procedure(s)

Restrictions on the performance, demonstration and teaching of these procedures are subject to legislation and will depend on the conditions of use of the techniques (research, private or commercial). The techniques are currently restricted to use by veterinary surgeons or the owner of the animals in non-research situations. However, any person using these techniques will require specific instruction and must demonstrate proficiency.

Demonstrator: Experience with these procedures. Thorough knowledge of the physiology, endocrinology and anatomy involved.

Students: Prior experience with handling livestock and background knowledge of anatomy, physiology and endocrinology is desirable. The extent of knowledge of the above required will vary with the intended use of techniques by the student (eg. research, commercial or other applications).

References

Descriptions of collection and transfer techniques, culture and storage and other aspects of the technology are given by :

Newcomb, R., Christie, W.B., (1978) Non-surgical recovery of bovine embryos. Veterinary Record 102: 414-417.

Sreenan, J.M., (1978) Non-surgical embryo transfer in the cow. Theriogenology 9: 69- 82.

Gordon, I., (1983) Embryo transfer in cattle. In Gordon, I.(Ed.), Controlled breeding in farm animals. Pergamon Press.