Test-tube technology: Using IVF on cows has numerous pros, cons
April 29, 2015
Steve Mohnen with Mohnen Angus can't take a lot of time to enjoy the fresh calves on the ground. He's got next calving season to think about.
In the cattle business there isn't much time to bask in the pleasure of success or wallow in failure. If a breeder isn't looking at least twelve months into the future, he is probably getting left behind.
The Mohnens of White Lake, S.D., have wrapped up their calving season and are busy artificially inseminating females for the 2016 calf crop. Because their customers appreciate the chance to buy half, three-quarter and full brothers and because it gives them the chance to rapidly grow their herd using proven genetics, the family also relies on embryo transfer (ET) and in vitro fertilization (IVF) in their breeding plans.
Mohnen said he has used ET for at least ten years and has been using IVF for about five. He is in the process of increasing his herd size and these technologies are helpful.
"What I like about it is the females. It seems like the daughters coming out of our donor cows are the ones we really like. If you want to expand your females, ET is the fastest way," Mohnen said.
While ET technology has been fairly commonplace since the early '80s and IVF since the early '90s, particularly in the dairy industry, Dr. Mark Allan with Sioux Center, Iowa–based Trans Ova, said that the use of ET technology has remained static for quite a few years, while "there has been a huge growth in uptake of IVF technology" in both the dairy and beef industries.
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Many of the cows on the Mohnen place are bull-bred or are watched for natural signs of heat and then AI-ed. But last week, 85 recipient cows were to be synchronized in preparation to accept frozen embryos from one of the Mohnen's top echelon of females – the donor cows. The technology to effectively freeze, then utilize fertilized embryos has developed in just the last couple of years.
"The average cow will only produce a few, if any, female offspring in her natural lifetime. IVF programs can potentially allow for one genetically superior cow to produce 10 to 25 female calves within one year," said Dr. Charles Looney of OvaGenix, a biotechnical company specializing in cattle breeding, based in Bryan, Texas.
Looney and his team produced the world's first cloned cow, the first transgenic cloned cow and the first commercial oocyte retrieval, or egg collection, and IVF programs.
Allan, Trans Ova's director of marketing and genomics, doesn't expect IVF to replace ET, but to continue to work in tandem with the older technology.
What is IVF?
Most producers are familiar with the embryo transfer process.
"IVF is almost identical to an embryo transfer; the only difference is in the embryo flushing method," Looney said.
It is a slightly more complex process where a veterinarian uses an ultrasound-guided needle to aspirate follicles off of a cow's ovary through the vaginal wall.
A vacuum system with a searchable filter is used to recover the contents of each follicle, including the important oocyte, or unfertilized egg. Once collected from the cow's ovaries, the filter is taken to a lab where it is rinsed and searched for oocytes with a microscope. The oocytes are then retrieved, counted and graded.
The recovered oocytes are placed into a special media that is designed to mimic the cow's uterine environment, including temperature and pH. This allows them to mature for 24 hours. The next day the oocytes are fertilized with semen and the resulting embryos are placed in an incubator for an additional seven days to mature. Embryos can then be evaluated, quality graded and grade one and two embryos are transferred into recipient animals that are seven to eight days post-heat, similar to conventional embryo transfer programs or vitrified, the freezing method used for IVF embryos for transfer at a later date.
The very first IVF procedure was done at the University of Georgia in 1981 and the method was perfected over the years using ovaries from slaughtered cattle. IVF struggled to establish itself as a legitimate technology because of low embryo production and pregnancy rates, making it unaffordable for most producers. It was often only used as a last resort for cows that could not produce offspring in any other way. With increased technology, today IVF is a practical and competitive reproductive tool with several applications.
"IVF gives producers a wider range of options than embryo transfers. Since follicles grow from the time of birth and are even viable recently after death, it gives producers more options in when and which cows they can collect from," said Looney.
Steve Yackley, manager of one of Trans-Ova's satellite centers, knows the ins and outs of growing test tube calves.
The practice is high risk but high reward, the Onida, S.D., man said. Practically, it is not cheap, costing a minimum of approximately $1,200 per attempt to flush one female, not including any of the costs associated with the recipient cows. But the cost is not fixed as there are a large number of variables including the number of embryos that need to be frozen, the possibility of using sexed semen, the success rate of gathering oocytes or eggs, and much more.
"These cows are unpredictable," he said.
While his IVF has produced some high dollar animals, including a Schaff Angus Valley bull that sold for more than $700,000 this year, it is not for the "meek of heart," Yackley said. "I think it's real important to communicate and talk to people about what their goals are, what they can anticipate, what their program is about."
What are the advantages of IVF?
IVF offers several advantages to producers over traditional embryo transfer programs, with the potential of a large variety of calves on the ground in a year.
Donor IVF aspirations can be performed every two weeks and semen from different bulls can be used to fertilize each of the oocytes from each collection, allowing for the opportunity for greater genetic diversity resulting from one cow. Embryo transfers result in five to six embryos each collection, which can only be done every 60 days.
IVF collections result in approximately 20 oocytes per aspiration and on average 30 percent develop into viable embryos, resulting in four to five grade one and two embryos per collection.
Aggressive IVF programs can result in more than 50 calves produced from one cow within a year. This is double the calf production achieved in conventional embryo transfer programs.
Six of Mohnen's ten National Western Stock Show champion carload bulls were produced from ET or IVF. Two were full siblings. On a practical level, Mohnen said his customers appreciate the ability to choose full brothers at their bull sale.
"Customers want full brothers or they like the idea that we are doing this because they know they are getting genetics from your best females," he said.
Mohnen said that bulls in their catalog are designated "ET" whether they are traditional ET or IVF.
Producers can start their donors on IVF programs as virgin heifers at 10 months old.
Since IVF does not involve the uterus, pregnant donors can still be collected throughout the first trimester of pregnancy, until day 100 to 120 of pregnancy, allowing producers to breed genetically valuable donors on time while still capitalizing on creating additional offspring.
Yackley said when a cow is about 100 days pregnant, aspiration becomes difficult or impossible as the growing calf falls over the pelvic wall, meaning the ovaries can no longer be manipulated.
Allan pointed out that producers can more quickly assess the genetic potential of a cow when they can raise 10 or more calves from her in just one year.
"It is kind of like looking at a litter of pigs," he said.
The Mohnens do not decide to use a cow as a donor until she has had at least two calves and looks to be on her way to achieving the American Angus Association's "Pathfinder" status, Mohnen said.
"South Dakota's mom, we do her as much as we can. We've got over 100 embryos in the tank."
Mohnen said he mates each cow with a variety of bulls.
"We use both performance and calving ease bulls on each cow," he said.
Donor cows that have been unable to achieve success with embryo transfers due to blockages, scaring, uterine infections, impassable cervices, overstimulation or because they make unfertilized or degenerate embryos are also good candidates for IVF.
"The reason you do IVF is because a certain cow didn't respond well to conventional ET. You get 50 percent when you get the eggs in but you are flushing her every 17 days," Mohnen said.
Mohnen said financially, IVF is the way to go when a cow proves she doesn't shed very many embryos with traditional ET.
"When you've got a really special cow, you want the best response. It is still cheaper in the long run than the ET if she only gives three to five embryos," he said.
ET often requires the use of two to three straws of semen to fertilize the egg. Since oocytes in an IVF session are fertilized in a microscopically controlled environment, significantly less semen is needed. One straw of semen can be used on the recovered oocytes from up to 12 or more donors, allowing producers to make the most of rare or expensive semen.
Utilizing sexed semen is more feasible using IVF because each embryo is individually fertilized in a lab, rather than using AI to breed the super-ovulated cow, Allan said. By the time a straw has been sorted for gender, there is not enough viable semen to AI a cow and successfully develop several pregnancies for ET.
IVF also has an advantage in that it can be done with fewer amounts of hormone shots and can even be performed unstimulated. It is not necessary to superovulate the cows, nor is it necessary to synchronize them. This is a major breakthrough since the donor cows are not exposed to hormones that might compromise the reproductive soundness of the animals, and they can be worked without prior preparation time for the procedure.
What are the disadvantages of IVF?
"Obviously the best environment to develop bovine embryos is within the uterus of the cow. We have not yet developed a compatible system," Looney said.
Embryos developed in a lab are not as hearty, which results in lower pregnancy rates and compromises freezability.
"The field is in the process of learning how to produce embryos for a wide class of cows faster and at a higher success rate. IVF was developed in the animal science realm of reproductive physiology and some vet schools are not yet teaching the procedure," he said.
IVF embryos transferred fresh yield on average a 50 percent pregnancy rate in well-managed recipients. This rate is slightly reduced with frozen IVF embryos. Studies have shown that embryo transfer leads to a slightly higher pregnancy rate, with seven percent advantage on fresh embryos and a 10 percent advantage on frozen embryos.
It has been shown that conception rates for embryos in cows during times of heat stress are better than traditional breeding. Transferring frozen embryos from conventional flushing during times of heat stress may help improve conception rates during the times that it is hardest to get cows to settle.
Folicle aspiration is an invasive procedure that can cause bleeding and infection which can create ovarian adhesions and requires a highly skilled veterinarian to perform.
The possibility of developing multiple calves from a coming 2-year-old heifer is exciting.
"You can have IVF calves on the ground the same age as her own first calf. Isn't that cool?" Looney said.
A cattleman who buys or raises a particularly special or valuable heifer might want to try this route, but obviously there is also great financial risk, Yackley pointed out.
"From a cowmen standpoint, you wonder how much money you want to put into a virgin female until you know she'll milk, take care of the baby, and be a good cow overall. You can get a lot of money invested in an unproven female but the technology is there if you want to do them," Yackley said.
Yackley pointed out the impatient nature of humans and the fact that the buyer of an expensive heifer might want to start the procedure right away in order to capture the popularity of genetics.
Not all donors will produce viable embryos. Ten to 15 percent of IVF procedures will result in no viable embryos.
Mohnen said if he flushes a cow a couple times and has no luck, he simply bull breeds or AIs the cow and moves on to another prospect.
Some instances of Large Offspring Syndrome where calves are born abnormally large have also occurred. While rare, they are generally correlated with matings where extreme birth weights are expected.
Is IVF economical?
It's no secret that IVF technology can get expensive with costs that typically double that of embryo transfer. However, the costs need to be analyzed on a long-term basis with costs offset by the overall long-term improvement of the herd. While the cost of the procedure is higher than embryo transfer, the actual cost per embryo is often lower.
"While it may be more expensive, it gives producers many more options," Looney said.
IVF programs allow for the greatest genetic progress in the shortest amount of time. Decreasing generation intervals serves to improve the genetic base of the herd.
No matter what your formula is for defining a "genetically valuable cow," the genetic basis of your herd improves with your selection intensity, defining what is important on your program.
"Some breeders are using IVF to maximize the impact of their very best cows or to rapidly increase herd sizes. For these purposes, IVF is a powerful tool. IVF is not for everyone or every cow, but more and more cattlemen are realizing that it has the potential to do things never thought possible before with other reproductive technologies," Looney said.
Old-fashioned pasture breeding will probably never be replaced. While customers appreciate the Mohnen's bull offerings of full siblings, they evaluate each bull individually. Sometimes the favorite bull is not from a donor cow.
"The ET or IVF calves are not always the sale toppers," he said.
Being able to develop more calves out of his favorite cows has been a major benefit to Mohnen, making better females, fast.
"For me, I think using ET and IVF has pushed my herd up at a faster level." ❖