Bovine embryo transfer helps ISU veterinarians improve herd genetics
Beef and dairy producers want the animals in their herds to possess the best genetics possible. But a cow can have only one calf per year, which places a natural limitation on how widely desirable genetics can be transmitted into the next generation.
That’s where a technique known as bovine embryo transfer comes in. It’s a growing practice among producers that required veterinarians to perform surgery in the past, but now can be completed with a much less invasive procedure that takes as little as 20 minutes. And veterinarians at Iowa State University's College of Veterinary Medicine are helping to make advances in this field by teaching veterinary students, training current practitioners and offering the procedure as a service.
On a recent morning inside a veterinary building just south of Ames, Marianna Jahnke, a lecturer of veterinary diagnostic and production animal medicine, and Dr. Tyler Dohlman, an assistant professor of veterinary diagnostic and production animal medicine, recovered embryos from a pair of black angus cows. One at a time, the donor cows ambled into a chute where Jahnke and Dohlman performed the procedure. Between 20 minutes and a half hour later, they ushered each cow back into an adjacent barnyard with little fuss.
Dohlman said embryo transfer has caught on increasingly among cattle producers over the last decade as the procedure has become far less invasive and practical.
“With embryo transfer, you can get many calves in a year from one unique cow with the same desirable genetics,” Dohlman said. “It makes the transfer of elite genetics much easier and more affordable.”
The embryo transfer process begins with cows receiving a hormone treatment to produce more than one ovulation (egg) at a time. The cows are then artificially inseminated with bulls also possessing desirable genetics. Seven days later, a veterinarian recovers the embryos by using a catheter and recovery fluid. The fluid passes through a specialized filter, which catches the embryos. Jahnke said the process produces an average of six good embryos per cow. Any fertilized embryos captured in the process can be transferred into a surrogate cow, called a recipient, that will carry the pregnancy to term, or the embryos can be frozen to be used later.
But searching for each tiny embryo requires a sharp eye and scientific acumen. After recovering the embryos from both cows, Jahnke took the filters into a lab and evaluated them under a microscope. The dishes used to hold the embryos are lined with grids that allow Jahnke to implement an orderly search pattern to make sure she doesn’t miss any. Jahnke carefully sifted through the fluid and tracked down a total of eight good embryos.
Sometimes the embryos, which are about 140 microns in diameter, become entangled with debris collected in the filters, so it takes a trained eye to spot them. And the veterinarians don’t know if each embryo was fertilized until they can evaluate them underneath the microscope to look at the integrity of the cellular structures. Some don’t get fertilized, and some don’t develop properly.
“It’s always a gamble until you see how many are fertilized and how many possess good quality,” Jahnke said.
Jahnke stored each successfully fertilized embryo in a small straw, which can be frozen and stored in liquid nitrogen until it’s needed.
The ISU College of Veterinary Medicine offers students and current veterinarians a range of opportunities to learn about embryo transfer. Veterinary students in their second or third year can take an introductory course, and fourth year students can spend two weeks on a rotation gaining hands-on experience with all aspects of the procedure. The college also offers veterinarians a short course focused on bovine embryo transfer.
“The growing demand for the procedure over the last decade makes this experience particularly valuable for students and veterinarians alike,” Jahnke said.