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Veterinarian View | November 2022

How to Increase Pregnancy Rates

contributed article by Dr. Vince Collison, Collison Embryo | Collison Veterinary Services, Rockwell City, Iowa

As we get closer to the breeding season for fall calvers, it is a good time to review things we can do to increase pregnancy rates. There are often things that are out of our control, yet there are many details in how we plan and execute that can make a difference.

Timing Matters

Allow enough time post calving before starting a synchronization program or using natural heats. When we use a 7-day CIDR program to synchronize cows, we wait until they are 50 days post calving before inserting a CIDR. This puts them at about 60 days post calving before they will be in heat. For a group of cows to be synchronized, the last cow to reach day 50 is the limiting time for the group to get synchronized.

When inserting a CIDR at day 50, this will still move a cow up 20 days in her calving next year. One thing we run into when someone wants to set up a group of cows to breed is that they try to schedule every cow together so they can get that last cow that calved into their synchronized group. What often happens in this situation is the first cows that calved will actually get set back in their calving the next year.

To avoid this, it is probably best to set up cows in multiple groups two to three weeks apart so that all cows can maintain their calving interval. We have often run into situations where the pregnancy rates were lower than normally expected and on review will often find that the post calving time before inserting CIDRs was shorter than what we normally would like. If using natural heats, we like to use a 50-day voluntary waiting period post calving before using any heats to AI or transfer embryos.

Thoughtfully Select Synch Program

Try to use a synchronization program that will increase the percentage of cows exhibiting standing heats. We have talked about using the 7&7 Synch program for this reason. It takes an extra week of time to set this up, but it will usually cause cows to come into heat a little quicker than a 7-day CIDR program and they will have a higher percentage that express standing estrus.

If you like to use the 7-day CIDR program, we like to give GNRH at 72 hours after removing the CIDR to any cows that haven’t shown heat. At the time we give GNRH, we will AI those non-responders or use them the following week for recipients. We find that the cows given GNRH that don’t display estrus will usually have a good corpus luteum (CL) and have as good of a chance for pregnancy as one that shows a heat. If they don’t have a good CL, we will pass on transferring an embryo to these cows.

If you’re going to AI a cow that receives GNRH, you won’t have the luxury of knowing if they will make a good CL or not. We still feel it is better to go ahead and AI these cows. Even if you get a 50 percent pregnancy rate on these GNRH cows, it is still better than not using them because they didn’t show heat. If we don’t give GNRH at 72 hours, we will have to continue to check for estrus and that can lead to a scenario where we are still checking for heats up to 7 days after removing the CIDR.

If you’re bringing in someone to transfer embryos it is really important to keep as many cows synchronized with the group as possible, so GNRH really helps with this. Also, if you are going to AI, you may have cows that are missed as the heat detection becomes more relaxed with time passed, cows come in through the night or may have silent heats. In the end, you may not AI as many as if you had just performed AI at 72 hours with GNRH to the non-responders.

Dropping Progesterone Levels

Get the progesterone levels in the cow to drop as fast as possible after removing the CIDR. Getting a cow’s blood progesterone to drop below 1 nanogram/decaliter quickly will result in a more fertile heat than a cow that doesn’t. A CIDR will produce a level of blood progesterone that will keep a cow out of heat and once it is removed the level of progesterone in the blood from the CIDR crashes quickly within an hour.

If a cow has a CL present at the time of CIDR removal, the prostaglandin injection given at that time will cause regression of the CL and progesterone it is producing. The problem is not all CL’s will regress at the same rate and can be the reason for cows displaying heats over several days and also having variability in the rate that progesterone will drop in the cow’s system.

One way to help progesterone drop quicker and faster is to give the injection of prostaglandin one day prior to removing the CIDR. This will initiate the regression of the CL and the progesterone it produces 24 hours before removing the CIDR. Thus, when you remove the CIDR, progesterone will be able to drop more quickly because the CIDR was the primary source at the time of removal. This can result in two things: more synchronized standing heats and increased fertility in a higher percentage of cows due to the more rapid drop in blood progesterone. We have used this on a limited basis due to the extra trip through the chute, but where we have the results have been very favorable.

While nutrition, genetics, and environment are all factors that contribute to pregnancy rates as well, we feel these are three things that are easy to implement and can make a big impact.

Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.

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