Breeding Decisions: IVF or ET?
Published on Wed, 11/21/2018 - 2:20pm
Breeding Decisions: IVF or ET?
By Jaclyn Krymowski for American Dairymen
What constitutes “elite cows” differs from herd to herd. For some it comes down to genomic merit, for some its production traits and profitability, yet others it’s all about type. Regardless of what category your elite animals fall into, they share the same common ground. This where you’d like to maximize your breeding potential. Careful sire selection is only one of the many tools at your disposal to accomplish that.
In-vitro fertilization (IVF) and embryo transfer (ET) technologies are both major options that can amplify the impact of each and every breeding. Deciding on which one to use and how can make the difference between lost opportunity and time or fasttracking to new replacements. For these reasons, both options continue to be increasingly common in the show and commercial worlds.
IVF vs. ET
Both of these technologies have the same end goal in mind. That is, they help to increase the rate of an animal’s genetic gain and her reproductive efficiency by increasing the number of calves she can have or introducing outside embryos to the herd. Both techniques may be done using either fresh or frozen embryos and have varying degrees of success. An experienced technician, in some states this must be a licensed veterinarian, is necessary to perform either procedure.
Embryo transfer, which involves flushing a super-ovulated bred cow with the resulting embryos being transfer to recipients either immediately or frozen for later. This method has a higher collection rate in comparison to its counterpart, producing five to six viable embryos per successful flush. Pregnancy rates are also higher, studies report as high as 60-70% when the transfer is done fresh and around 50% when frozen. Economically, this factors into an overall lower average up-front cost.
A bonus to ET is that it is accessible to most farms due to its wide practice and relative simplicity. This is because these embryos are fairly hardy and not environmentally sensitive. However, this procedure can only be done every 45-60 days. For obvious reasons, it is also best done with sexed semen which can add to the cost and take more units to procure a pregnancy.
Some estimates show that ET will cost at least $250 per viable pregnancy, variable to the price and amount of semen used. Sometimes this is justified by the value of the resulting calf. Some operations set an X value that the offspring of a particular animal must have to be worth the investment in additional reproductive technology.
In-vitro fertilization is an excellent option for heifers too young to yet be traditionally bred, spring boarding their productive life and genetic impact on the herd. In this procedure, the cow is not bred prior to flushing and the aspirated oocytes (unfertilized eggs) are fertilized in a lab. This can also be done far more frequently than ET, as much as weekly or biweekly.
This method can be successful with animals that aren’t able to be a prolific ET donor. However, this option can also be/ more difficult to get a viable pregnancy out of. A successful flush averages only four to five oocytes for fertilization. There is only a 50% chance of pregnancy when done fresh and 55-60% frozen. They are also much more delicate and are very temperature sensitive and require a temperature-controlled room for aspiration. This means you will have to either find a nearby collection facility you can transport your animals to or find a farm that has on-site facilities available to use.
Selecting an option
Cows that aren’t having much luck getting live calves from transfers are worth trying in IVF. Some of the issues IVF can work around are oviduct blockages, abnormal ovulations, or issues with progesterone and corpus luteums. Heifers as young as seven or eight months old are also eligible for this procedure.
However, IVF is not for all animals either. It will not be successful on donors that have low antral follicular counts and poor oocyte producers.
If you are looking to get more embryos per flush, want the higher conception rates and the lower up-front cost obviously ET is your go-to option. If your cows are open and prolific ovulating donors, they should be good candidates. This method is primarily for your proven breeders. It doesn’t work well with virgin heifers, poor ovulators or impacted by other various reproductive issues.
Of course, there are many extraneous factors that will vary from farm to farm. These may include budget, number of animals to breed, availability of trained technologies and equipment and other resources. Take a look and see where in your area these practices are being implemented.