Superovulation Basics
contributed article by Dr. Vince Collison, Collison Embryo | Collison Veterinary Services, Rockwell City, Iowa
One of the most common questions we get is, “Why won’t my donor flush better?” It’s a pretty simple question that encompasses a lot of complex issues.
Superovulation Process
Probably the first thing to address is what is going on when we superovulate a donor. The ovaries are very dynamic organs that change from day-to-day. Cows will have waves of follicles develop every 7 to 10 days. During the middle part of a 21-day cycle these follicular waves start out with a group of follicles, but they regress as one follicle becomes dominate and continues to develop.
The same thing happens at the end of the 21-day cycle, but the dominate follicle will continue to grow as the corpus luteum regresses and will be the follicle that ovulates when the cow comes into heat. The purpose of stimulating a cow with FSH (Follicle Stimulating Hormone) is to recruit the small follicles that are present in the current wave of follicles during the middle of her 21-day cycle. So, knowing these basics, here is what we can do better to improve her response.
Improving Response
1. Examine ovaries with an ultrasound 1 to 2 days before starting her on FSH. If a cow has a cyst or a dominate follicle present at the time you want to start FSH, the response will be poor. Dominate follicles have a suppressive effect on the other smaller follicles and will usually result in poorer response.
The best way to correct this is to do a dominate follicle removal (DFR) if needed with an aspiration probe at the time of the ultrasound exam. This immediately removes the effects of the dominate follicle, allows smaller follicles to continue developing, and will help improve odds of a better result.
2. Genetics can play a large role. When doing ultrasound examinations of cows, you can get some idea of what kind of follicular reserves a donor has. On cows with large responses you usually see lots of little follicles sitting under the surface of an ovary. The cows with poorer responses won’t have these follicular reserves present.
Cows that have typically good responses to superovulation will usually have daughters that also respond well. The same holds true with poor responders, their daughters usually aren’t large responders. When giving FSH you can only recruit follicles that are available to recruit.
3. Nutrition has to be right. Follicular dynamics are heavily dependent on proper nutrition. Make sure that the donors are getting proper amounts of trace minerals and vitamins. We prefer that chelates are used in the mineral to improve absorption. A lot of complex enzyme reactions occur during follicular development and depend on trace minerals and vitamins.
The main source of energy in the diet should be from fiber-based energy sources. When concentrates increase in a ration, the response to superovulation is usually reduced. For a cow’s reproductive physiology to be right, her rumen has to be right. If a cow’s nutrition has not been right, it can take several months on an improved diet for her to get back into a good physiological state.
These are probably the top three things we look at when trying to improve response to superovulation.
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Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC
in Rockwell City, Iowa.