The genetic potential of the herd is an important resource in any dairy operation. The role that embryo transplants can play in taking advantage of and even expanding that potential is a management tool all dairy producers should keep in mind.
Dr. Jack Reeb, from Central Canadian Genetics in Lockport, Manitoba has been involved in flushing, freezing and transplanting embryos since 1980. Dr. Reeb says fewer people are doing embryo work now and those who are flushing cows are generally breeders with superior animals who specialize in producing high-quality replacement cattle for the domestic and export market. The reason is simple: the process is not cheap and the resulting embryos have to be of a high enough quality to warrant the expense.
“The cost of collecting and transferring a viable embryo, either for freezing or transplanting is $200,” says Reeb. “To that, you have to add semen costs of $100 or more and drug costs of about $200 per flush. An average number of viable embryos per flush in dairy cattle is about five whereas in beef cattle, it is closer to 5.5.”
On the other side of the ledger, Reeb notes, dairy producers are already incurring high costs when they service cows a couple of times with semen from high quality bulls. Going with embryo flushing means getting, on average, three times the number of viable embryos per dose of semen. The other advantage, needless to say, is getting more calves from the best quality cows in the herd, either as replacements or for sale to other producers.
Rob Berry, the dairy business development specialist with Manitoba Agriculture, Food and Rural Initiatives, says producers usually look at only the best of the best when flushing for embryos.
“Typically, producers are flushing very high-end cows,” Berry says. “We’re talking about animals in the top 10 percentile when it comes to Lifetime Productivity Index (LPI) and a Breed Class Average (BCA) up in the high 200’s.”
He says a breeder looking to sell replacement heifers into the show cattle market or bulls for stud farms may also be looking for specific confirmation traits and this may affect which animals are selected for flushing.
Dr. Richard Hodges, is the director, animal care and use programs, at the University of Manitoba and previously worked in private industry. He emphasizes the importance of selecting donor cows that are reproductively sound and are cycling properly.
“That’s really the first step in the process,” he says. “A donor cow has to be in good condition physically. If she’s not in the best of health, her eggs won’t be as viable as they should be. Anything that stresses the cow, including very hot weather, should be avoided.”
Don Penner of Benner Holsteins northeast of Steinbach, Man. is a dairy producer who has been flushing dairy cows for embryos for 30 years. A pioneer in the field, he says certain cow families are just naturally more fertile and therefore better suited to the flushing process.
“There is some trial and error involved,” Penner says. “But certainly, you want them to have enough condition to flush and to flush well.”
Penner estimates over the course of her lifetime, a good donor cow can produce an average of 30 embryos.
Once the appropriate donor cow has been selected, the next stage is to administer a follicle-stimulating hormone (FSH) in order to “recruit” — as Hodges says — more eggs. Another hormone, prostaglandin, is also given to regress any CLs or corpus luteum that would prevent the cow from coming into heat.
When she does come into heat, the cow is bred, perhaps two or three times, depending on the duration of the heat. Typically, semen from the same bull will be used each time. This makes genetic identification of the embryos easier. As well, some producers will use sexed semen although the use of sexed semen sometimes results in lower conception rates and therefore less viable embryos.
Seven days after breeding, the cow is ready for flushing. Hodges says it is always a good idea to check the cow for the formation of CLs — this means there has been a response to breeding efforts and there should be good embryos for flushing. The actual collection of the embryos consists in inserting a silicone catheter in each uterine horn through which a commercial embryo flush medium is injected. At the same time, the person performing the flushing tips the uterus so that the embryos get caught in the fluid and travel down for collection. The collection fluid is then extracted from the donor cow and filtered to remove the embryos.
They are very small at this point: about eight embryos fit into a single millimetre, estimates Hodges. However, with the help of a dissecting microscope, they can be examined and graded. Only grade one and two embryos are frozen — these are the most viable ones. Lower quality embryos can still be viable: they must be transferred immediately to recipient cows that have been managed to come into heat at the same time as the donor cow is flushed. The embryos that are to be frozen for export are subjected to a treatment with an enzyme called trypsin which cleans them completely and prevents transmission of any disease.
Embryos are frozen in ethylene glycol. This draws the water out of them and prevents the formation of damaging ice crystals which would render them unviable. The freezing process can take up to one hour as the temperature is lowered gradually to -30 C to -35 C. The embryos can then be placed into liquid nitrogen where they can be stored, transported and sold.
When asked about critical factors for successful embryo flushing, Hodges comes back to the condition of the donor cow. She needs to be in good health and stress-free. The same applies to any recipient cows to which embryos are to be transferred. The process also needs someone who understands enough about the cow’s reproductive physiology to do the job right. Typically, this means employing a properly trained veterinarian. In fact, anyone selling his or her services in the embryo transplant field in Manitoba has to be a vet. Using the right materials for storing and manipulating the embryos is also critical, says Hodges — even the materials used for the catheters can have a huge impact on the viability of the embryos.
Don Penner says when all is said and done, you’re probably looking at total costs of $500 per embryo. So whether or not embryo flushing is worth the cost and hassle comes down to the gain in productivity that can be reasonably expected from the resulting animal — if embryo flushing and transfer is done within the herd — or what the frozen embryo can fetch as a replacement or show animal in someone else’s herd. Penner, who sells embryos both in the domestic and export markets, says he can get anywhere from $1,000 to $2,200 for a frozen Holstein embryo from his herd. It is clear, for operations like Benner Holsteins with a reputation for selling high quality genetics, embryo flushing makes sense. The benefits for individual producers working with the genetics in their own herd are a little more difficult to establish.