Beef Cattle Embryo has become one of the most exciting and progressive procedures available to today’s producers. With conventional production, the average cow produces six to seven calves in her lifetime.
Embryo transfer can increase her reproduction efficiency to numerous calves per year, thus increasing your selection opportunities many times. Along with artificial insemination, embryo transfer offers progressive producers fascinating genetic opportunities.
Selection of Donors
When pursuing a Beef Cattle Embryo Transfer program donor selection should be based on several criteria. Genetic superiority is of major importance and should be evaluated with the following traits in mind: birth weight, milking ability, pre-weaning growth, post-weaning growth, and carcass cutability. Official sire summaries can assist in measuring and comparing the above traits. Records should be used to evaluate maternal breeding value, weaning breeding value and yearling breeding value.
All of these values are objective measurements based on pounds of gain as measured on a scale. Ultimately, value of progeny must justify an embryo program. Reproductive ability is the second main criteria to determine donor selection.
To enhance the success of your beef cattle embryo transfer program, the donor should meet the following characteristics: 1) two or more years of age, however, heifers can and have been used successfully in embryo transfer programs, 2)regular calving each year, 3) conception after one or two services, 4) regular estrous cycles, and 5) no history of retained placenta, metritis or cystic ovarian disease.
Sire selection is based on the use of well proven bulls that produce high quality semen. By using reference sire summaries, the producer can evaluate EPDs for birth weights, weaning weights, yearling weights and milk production to assist with sire selection.
Pre Transfer Preparations for the Donors
Blood or hair samples should be submitted for typing or DNA analysis approximately two months prior to flush date if possible. This insures the results are completed before pregnancies result and that the calves can be registered.
Materials for taking this sample are available from your breed association. Other breed requirements must be determined before transfer as well.
The following vaccines should be given within the last six months: IBR/BVD, BRSV, 7 Way Clostridial, 5 Way Lepto, and Ivomec. These vaccines should be given at least 4 weeks prior to embryo collection and transfer.
Superovulation consists of injecting the donor cow with a fertility drug, FSH (follicle stimulating hormone), to induce multiple ovulation. Injections begin on approximately the tenth day after estrus and consist of twice daily injections of FSH for four days.
On the fourth day of the FSH injections, prostaglandin is also injected to cause the regression of the corpus luteum. This triggers estrus one and a half to two days later. The donor is artificially inseminated with one unit of semen at first observed standing heat.
Twelve hours later, she is bred again using two units. At 24 hours she receives 1 additional unit of semen. Variations to this breeding schedule will be used depending on the history of the donor, quality of semen used, and cost of semen
Recipients should be healthy, of medium to large frame, on a gaining plane of nutrition and cycling regularly. In addition, they should be vaccinated for Brucellosis (with an official calfhood vaccination tattoo in the right ear), Rednose, Virus Diarrhea, BRSV, Parainfluenza 3, 5 Way Lepto and 7 Way Clostridial vaccine, and Ivomec.
Recipients will be synchronized with prostaglandins to be in estrus the same time as the donor cow. Those in estrus within 24 hours before or after donor estrus can be used as recipients.
Since there is no way to predict the number of embryos produced by the donor cow, a sufficient number of recipients are synchronized to anticipate average collection. Ten to fifteen recipients per donor is the usual estimate.
When embryos are to be frozen, a few recipients should be prepared to implant lower grade embryos which are not freezable.
Collection of Embryos
Non surgical techniques are used to recover embryos seven or eight days after estrus. The donor is given an epidural block in the area of the tailhead to prevent straining. The vulvar area is scrubbed to prevent contamination.
A flexible rubber tube called a catheter is gently threaded through the cervix and up into the uterine horns. A small rubber balloon cuff is inflated with fluid to expand and fill the uterine lumen. This prevents any backflow of fluid. There are several holes near the tip of the catheter that precede the inflated cuff. Fluid enters the uterus by means of these holes after being injected through the catheter with a 50 cc syringe.
Once the fluid is in the uterus, the horn is gently massaged and the fluid (containing the embryos) is drawn back out through the catheter. This process is then repeated in the other uterine horn. The embryos are collected in a zwitterionic buffer solution containing antibiotic/antimycotic.
The fluid flushed through the uterus is filtered through a special filter that traps the embryos but allows the fluid to drain free. All but 50 cc is drained through the filter. This remaining fluid, containing the embryos, is divided into several scored petri dishes to be searched.
The embryologist searches each dish under a dissecting microscope and upon finding an embryo, removes it with a pipette to be transferred to a small petri dish. All the embryos are placed in these small dishes to later be washed, identified, and classified.
Transfer of Embryos
Non surgical. Embryos to be transferred non surgically are aspirated into 0.25 ml artificial insemination straws. Air bubbles are placed on either side of the fluid containing the embryo. The straw is fitted into a cassou gun, which is covered with a plastic breeding sheath. The cassou gun is similar to an A.I. gun but slightly longer so that it can go deeper into the uterine horn.
The recipient is placed in a squeeze chute and given an epidural. After being palpated for a corpus luteum, the cassou gun is inserted mid way up the uterine horn of the recipient and the embryo is deposited in the horn ipsilateral to the corpus luteum. This technique takes considerable practice to achieve satisfactory pregnancy rates.
From the average donor, approximately eight to ten embryos are collected. Several of these may be unfertilized or degenerate. Approximately seven embryos are of transferable quality and on the average, four or five pregnancies will result after their transfer.
Approximately 65% of fresh and 60% of frozen embryos result in pregnancies. Your success rates may vary greatly because every donor is different. Some donors will consistently produce large numbers of excellent embryos, while others may only produce a few.
For beef cattle embryo transfer to be successful, it is essential to pay the strictest attention to detail, thus minimizing any outside influences on the success of the transfer.