EMBRYO TRANSFER IN CATTLE

EMBRYO TRANSFER It begins with selection, superovulation, and artificial insemination (A.I.) of the donor animal. Next, the embryos are recovered from the donor through either surgical or nonsurgical means, evaluated, and then frozen or transferred fresh. Lastly, the recipient animals are synchronized to be in the same stage of the estrous cycle as the donor when the embryo was recovered and receive the embryos through surgical or nonsurgical techniques

WHY..?? The potential for genetic improvement in the herd. With embryo transfer, superior female genetics can now be spread across a specific herd or even many herds. Eliminating the stress of parturition on a desirable animal, thereby increasing her reproductive life span. Disease control, salvage of reproductive function, and potential twinning.

HORMONES Follicle Stimulating Hormone. The FSH is taken from a cow's pituitaries, which is a gland in the brain that produces growth hormones and sex hormones (traditionally superovulation of the donor animal involved the Pregnant Mares Serum Gonadotropin, but due to ease of administration, superovulation treatment often utilize FSH). Prostaglandin F₂A, results in ovulation approximately 48 hours after the prostaglandin administration.

PREPARATION 5-6 mg of follicle-stimulating hormone (FSH) given twice daily for 4 days. This dose is gradually decreased each day (for example 6,6,4,4,2,2,2, and then 2 mg of FSH). Give luteolytic dose of prostaglandin F2a (PGF2a) on day 3-4. This results in ovulation approximately 48 hours after the prostaglandin administration. This particular treatment regime requires the donor has a well formed corpus luteum (CL) and is between day 8-13 of her cycle. In superovulated animals, the ova are released over a 6-12 hour period. Therefore, the cow should be inseminated 2-3 times, at 12 hour intervals, beginning 12 hours after the onset of standing heat. Each cow will vary tremendously on the dose of FSH required and the response she has to the FSH. Most cows will produce 5-7 viable embryos, while others may produce very low numbers of embryos.

AREAS FOR CONSIDERATION Watch for indications of approaching estrus. donor stands and allows another cow to mount her (#1 sign) Restlessness decreased milk production off feed clear, mucoid vaginal discharge Donor animal(s) should not be left alone (a group of approximately 10 other animals is sufficient). Pens used should not be slippery or too crowded.

Because semen is so sensitive to temperature changes, proper semen handling is essential for good results. The semen used should be evaluated for proper morphology and intact acrosomes prior to use. A high quality semen tank should be used with liquid nitrogen levels checked regularly. Straws should be carefully removed and thawed in a 95° F (35° C) water bath for 40 seconds. The straws are then wiped dry and placed in a prewarmed insemination rod. The insemination rod is then placed under clothing to prevent damage from direct sunlight and/or cold shock. The donor animal must then be inseminated immediately. The semen is placed in the body of the uterus about 2 cm in front of (cranial to) the internal cervical os. * Failure to follow any one of the above procedures will result in a decreased number of fertile ova

CONCEPTION RATE With embryo transfer an already fertilised egg is being inserted, which eliminates one of the steps of artificial insemination so the conception rate should be 5 - 10% higher than artificial insemination, but a lot depends on the condition of the recipients. On an A.I. program the conception rate is 60 - 65% while on an embryo transfer program it is expected roughly the same sometimes a bit higher.

SUITABLE TEMPERATURE Fresh embryos can be stored at 37ºC for 6 - 8 hours without much harm but it is recommended that the embryos are inserted into the recipient cow or frozen as soon as possible. The embryos are frozen in liquid nitrogen, they can be stored in this for ever.

SURGICAL EMBRYO TRANSFER Definition: -involves the collection and transfer of embryos from genetically superior cows to donor cows. Embryo collection requires penetration of the abdominal cavity and flushing of the oviducts. The collected embryos are then transferred to donor cows by laparotomy (surgical) or laproscopic technique which also requires penetration of the abdominal cavity.

LAPAROSCOPIC TECHNIQUE Involves the penetration of the abdominal cavity and deposition of semen directly into the uterus of cow in oestrous. In addition, gas is inserted into the abdominal cavity through a second abdominal penetration to assist insemination. Carried out by stud breeders with the main aims of breeding stud rams and improving the genetic merit of progeny.

SURGICAL EMBRYO TRANSFER PROCEDURES Cows must put under general anaesthesia. Recipients are placed in squeeze chutes that gives access to either flank. Corpus luteum is located by rectal palpation and the flank ipsilateral to the CL is clipped. Washed with soap and water, and sterilized with iodine and alcohol. About 60 ml of 2 percent procaine is given along the line of the planned incision. Makes a skin incision about 15 cm long, high on the flank, just anterior to the hip.

Muscle layers are separated, and the peritoneum is cut. Inserts a hand and forearm into the incision, locates the ovary, usually about 25 cm posterior to the incision, and visualizes or palpates the corpus luteum. Uterine horn is exteriorized by grasping and stretching with the thumb and forefinger the broad ligament of the uterus, which is located medial to the uterine horn. Using about 0.1 ml of medium in a small glass pipette (<1.5 mm outside diameter), an assistant draws up the embryo from the storage container. Pipette is then inserted into the lumen of the uterus, and the embryo is expelled. Incision is then closed, using two layers of sutures. The surgery takes about 15 minutes.

ADVANTAGES OF THE SURGICAL EMBRYO TRANSFER 1. Allows an animal to have many offspring than normal 2.Increasing accuracy of selection and selection intensity 3.Safety way to import and export germ plasm 4. Best way to preserve germ plasm for the future

DISADVANTAGES IN EMBRYO TRANSFER 1. Increased expenses and higher break-even costs for calves. 2. Estrus detection required. 3. Synchronization of recipient is challeging and therefore 2-3 embryo recipients are required for every donor. 4. Specialized equipment and trained personnel. 5. More expensive and time consuming than traditional reproductive methods/conventional breeding methods.