Embryo Transfer in Cattle - What Is an Embryo Transfer?

Embryo Transfer in Cattle

What is an embryo transfer? Embryo transfer (ET) refers to a step in the process of in vitro fertilization (IVF) when one or several embryos are placed into the uterus of the recipient cow to establish a pregnancy (Seidel 1991). Embryo transfer in cattle is beneficial to the cattle and to the farmers who reproduce their cattle using it. This essay will explain how it benefits the farmer and also will explain how embryo transfer works, explaining each stage of development and the reasons why things are done the way they are.

Farmers use embryo transfer for many different reasons. Even though it is not natural, it's the way most farmers breed now days. It gives them access to sires and dams that they could not get with natural breeding. With embryo transfer you can make a lot more baby calves with a single cow that either gives a lot of good milk or is a really good show cow. Farmers can get multiple daughters from a single flush, and then they can either keep them for themselves or even sell some of the daughters in a cow sale for a good amount of money. Also by flushing the better cows in the herd and putting the eggs in worse cows, it allows you're herd to produce better calves and then become more profitable.

There are potentially about 150,000 eggs or ova in the female cow and billions of sperm produced from a single male. When a cow is bred naturally, only a fraction of the reproductive potential is used. The average herd bull will only sire 15 to 50 calves per year while the average cow will have at most one calf a year unless she has twins. With artificial insemination (AI), you basically have an unlimited amount of sperm produced by a superior bull. The female cow will produce about eight to ten calves in her life time under normal circumstances. Like AI has done for the bull, ET is a technique that can greatly increase the amount of offspring a single cow will produce in a lifetime. If you wanted to greatly improve your herd number it will take anywhere from 10 to 20 years to accomplish. By using AI, the same improvements will only take about seven or eight years. If you wanted to improve your herd in less time then using ET will only take four to five years. New technology has helped give further control over what the sex of the offspring will be by using sexed semen (Blezinger 2007).

In order to perform a beneficial embryo transfer you need to have a genetically outstanding cow. If you took embryos from a bad cow then the daughters of that cow would most likely turn out like their dam. So choosing a donor cow, she needs to produce outstanding milk, have great health traits or perform at a high level in the show ring. It is possible a cow may have all of these benefits and if that's the case, then the sale value of her daughters will be very high or if you wanted to keep them for yourself you could have more outstanding cows in your herd. After picking out a cow that stands out, there are more details to look over before continuing with the operation. She should be at least 60 days postpartum before the transfer procedure begins. The cow needs to have regular estrous cycles commencing at a young age, a history of no more than two attempts at breeding per conception, and she cannot have any conformational or detectable genetic defects (Toxel).

Once you choose your donor cow then it is beneficial to keep her in a box stall or clean pen where you can keep a good eye on her. Normal nutrition level plays a big role in both the donor and recipient cows, if the cow is obese or very thin, then she will have reduced fertility, so it is important to maintain a steady nutrition level for her appropriate size and level of milk production. High stress levels can cause the mother to lose the embryo. Reasons for high stress can come from extreme weather conditions or some kind of sickness. That is why keeping them in a box stall is very beneficial (Hansen 2002). Heat stress is a major factor contributing to low fertility of dairy cows inseminated in the late summer months. In the hot summer months, the conception rate can decrease from 20 to 30% compared to in the winter months (Anonymous).

The next step in the ET process is the superovulation of the donor cow. Superovulation is the release of multiple eggs at a single estrus. Typically people do not flush heifers because they have not yet calved out so they do not know what they will look like after or what their milk production will be. Cows that are treated the right way can release up to 10 or more good eggs at just one estrus. On average 85 percent of normal fertile donors will produce about five transferable embryos. Some cows that are superovulated every 60 days can produce less and less eggs over time. The main purpose of superovulation is to stimulate extensive follicular development with the use of follicle-stimulating hormone (FSH). Different reproductive veterinarians may perform different superovulation protocols, but generally, FSH preparations are infected twice daily for four days at the middle or near the end of their normal estrous cycle, while a functional corpus luteum (CL) is on the ovary. On the third day of the treatment, a prostaglandin injection is given causing CL regression and estrus to occur anywhere from 48 to 60 hours later (Toxel).

Proper insemination of the donor female is a very important step in the ET process. Superovulation creates multiple eggs that will be released over the course of several hours. It is very important that viable sperm cells reach the oviducts of the superovulated females. Because of the variability in the number of eggs and the timing of their release, females will be inseminated anywhere from one to three times during and after estrus. One scenario that has been used successfully is to inseminate the superovluated cow at 12, 24, and 36 hours after the onset of standing heat. High quality semen with a high percentage of normal, motile cells is very important so that you end up with better results. As with AI, semen should be placed in the body of the uterus. The body of the uterus is a small target that is located in front of the cervix. If the inseminators deposit the semen into one of the uterine horns, it will reduce fertility if ovulations are taking place at the opposite ovary (Selk).

Embryo recovery or the "flush" typically takes place six to eight days after the beginning of oestrus. The donor cow is given an epidural block at the tail head to prevent straining. A small synthetic rubber catheter is inserted through the cervix and into the body of the uterus of the donor cow. Then the cuff is inflated with saline solution to hold the catheter in place and it also prevents backflow of liquids. Saline solution is flushed into the uterine horns through the holes