A new technique called preimplantation diagnosis can identify genetic mutations in embryos before putting them in mares, allowing breeders to avoid having a foal with some life-threatening genetic conditions.
Animal welfare is at the forefront of horse owners’ minds, but in truth, cost for anything is also a factor in breeding, training and competing with a horse.
In Part 2 of this article, we will explore the cost and practical uses of this technique. Click here to read part one, which explained the technique.
For breeders who are focused on producing competitive horses, the initial cost to perform genetic diagnosis may seem high, but it is far outweighed by the expense that accompanies caring for a mare who carries a foal affected by a debilitating disease to term.
“Ethically, it is one thing to test, but then when you look at cost, it is easier to pay up front than having to potentially euthanize,” Smith said. “When we breed a mare that is not a carrier to ‘Cat,’ we don’t test those embryos because there isn’t a question about the foal [being homozygous for HERDA]. But carriers that we breed to High Brow Cat, when we ICSI them, we do test them.
“It costs a couple hundred dollars off the bat, but that is much cheaper than $3,000 for a recip, the hundreds of dollars to take care of her until she foals and the other costs. The immediate cost is much less than later, if looking at it from a financial standpoint.”
Hinrichs describes the procedure for genetic testing an embryo as cumbersome for people using conventional breeding methods, since the embryo must be flushed from the mare, biopsied and then transferred to a recipient mare. Generally only facilities that handle ICSI also perform biopsy for preimplantation genetic analysis. But, when breeding via ICSI — which is required for stallions who have limited semen availability, such as High Brow Cat — the procedure typically costs far less.
“For someone just breeding their mare conventionally, this is expensive and involved. You have to flush an embryo, package it and ship it to a lab,” Hinrichs explained of the process. “After biopsying it, the lab has to freeze the embryo or it has to be transferred while awaiting the results, and if the results are unwanted, then you have to short-cycle the mare to terminate the pregnancy at 10 days. It is much easier when embryos are produced by ICSI, because they are already there, in the laboratory, and they are small enough to easily freeze after the biopsy is performed.”
For Smith, the cost is one she can carry when it means taking the guesswork out of whether or not one of her HERDA-carrying Smart Little Lena daughters bred to High Brow Cat will have a foal that is affected with the genetic mutation.
Beechfork Ranch opts to freeze the embryo that is biopsied while the recovered cells are sent to the University of California-Davis for genetic testing. The embryo is not transferred to a recip mare until they receive the lab results. Another added bonus of preimplantation genetic analysis is learning the sex of the foal. “We bred a HERDA-carrier mare to High Brow Cat last year, and we got five embryos that we froze and tested,” Smith said. “We had five fillies — three HERDA negative-negative and two carriers. It is nice to know and also, it’s nice to know that you are getting fillies or colts. That is another useful aspect of it.”
So, if the procedure provides breeders and owners with so much information, why isn’t it more widely used? Smith believes it is partially due to a lack of information about the process. In addition, some hypothesize HERDA carriers have an athletic advantage, especially in sports like cutting. While there has been some research into this concept, it is not proven. “When I first started out, I thought horse breeders would want to eliminate these mutations from the breed. Then, I found that some breeders and trainers thought them advantageous in the heterozygous carrier state,” Hinrichs said. “I’ve heard people say with HERDA that horses are more bendy or flexible, and it gives them an extra edge,” Smith said. “Genetically, I don’t think there is an advantage or disadvantage. The best mare we’ve ever had, Cromed Out Cat — a daughter of High Brow Cat [out of Peptos Fancy Jewel x Peptoboonsmal] — is HERDA negative-negative, so she didn’t have an extra edge because she is a carrier. There are plenty of great horses that aren’t HERDA carriers.”
A Practical Use
Breeding horses is often described as an art form, but to many, the use of embryo transfer, frozen semen, ICSI and other similar methods to produce foals is less art and more science. Still, breeding always comes down to selection.
“I don’t see any ethical issue with embryo biopsy, because by just breeding animals, we are selecting,” Hinrichs said. “You select which stallion you want to breed your mare to, which mare in your herd to breed; you select which foals to keep at birth and show. Animal breeding is all about selection, so selecting the embryo that isn’t going to carry a potentially life-ending disease is good from an animal welfare position and even from an unwanted horse standpoint.”
Hinrichs said typically only facilities that handle ICSI and a few university labs can perform embryo biopsy. She is also opening a new facility at the University of Pennsylvania’s New Bolton Center. Hinrichs worked with the scientists at UC Davis to optimize methods for genetic analysis of the recovered cells, so almost all genetic analysis of biopsied cells is done there. General practice veterinarians and facilities that handle general embryo transfer are not usually equipped for the complex technical work of performing the biopsy.
“Currently, most of the avoidance of producing affected foals is by not breeding your carrier mare to a carrier stallion. Of course, that limits your choices if many of the top stallions in your breed are carriers,” Hinrichs explained.
“When I first promoted embryo biopsy for preimplantation genetic diagnosis, I thought that it was a way for breed registries to eliminate the disease effectively from their breed. You could still breed every mare and stallion in the gene pool, but transfer only embryos with two normal genes. In one generation, the genetic mutation could be eliminated from the breed.”
The turnaround time on testing can be a week or more, which may sound like a lot of downtime during a busy breeding season, but it is a short period to wait when the alternative is possibly an affected foal, with little to no quality of life.
“I wouldn’t think that breeders who knew about this would not take advantage,” Smith said. “A lot of people don’t know this technology is available, but it is an option. I don’t condone breeding [carriers] to carriers and taking a chance [by] not testing, because there is technology available to avoid that situation. If you can avoid an issue like that when breeding, you should do everything you can to not pass it on.”
Katrin Hinrichs, DVM, Ph.D., has led multiple research efforts in equine reproduction, including developing the technique now used to analyze embryos from horses that carry a disease-related mutation.
*This story was originally published in the July 1, 2020, issue of Quarter Horse News.