Preg Checking: Ultrasound vs. Arm

I often get asked the question, “Hey Doc, should I ultrasound (U/S) or arm my cows this year?”

The answer to this question depends on a few things. 1. How far bred are they? 2. Are you looking to separate artificially inseminated (A.I.) from bull bred? 3. Are you selling them? 4. Do you need to eliminate opens as soon as possible? 5. Who is pregnancy-checking your cows? Let’s look at each question to answer the original question of U/S or sleeving.

1. How far bred are they? To age a fetus with the U/S, they must be done before 100 days pregnant. After the fetus is over 100 days, we can no longer get the whole calf on the U/S screen and, therefore, can’t accurately see it. We can pick up pregnant or open but not age the fetus.

2. Are you looking to separate A.I.’s from bull breds? Again, we want to do this before the fetus is 100 days old. Ideally, we would ultrasound these girls around 45-50 days post-A.I. All confirmed pregnant animals would then be sorted off or tagged, and all open animals would be rechecked 45-50 days later. If you want to contain pregnant females into more groups, ultrasounding every two weeks after the initial check at 45-50 days works very well.

3. Are you selling them? Most producers want a short calving period, increasing their willingness to pay a premium for a tight calving window. The best way to accomplish this is by ultrasounding every two weeks, starting after the initial check at 45-50 days, and tagging pregnant animals with a different color ear tag for each two-week period. Remember that all gestation lengths are not the same. As anyone who has time A.I.ed knows, even though everyone was A.I.ed on the same day, they don’t all calve on one day. Gestation lengths are an average, and many outside factors, including stress, weather, and genetics can have an influence.

4. Do I need to eliminate opens as soon as possible? This question is answered by answering a couple of other questions. Do I have a feed shortage, or can I hit a higher market with the opens if they are sold right away or if I put them in the feed yard and put extra weight on them? We can pick up a fetus about seven days earlier with an U/S than by manual palpation.

5. Who is preg checking? New veterinarians coming out of veterinary school have had the advantage of seeing, on a screen, what their fingers are feeling in the animal. When I was in vet school, we had one U/S machine for the whole class and were threatened that if we broke it, we would fail the class. Therefore, we had to learn what we were feeling by describing what we felt to the instructor and practicing with reproductive tracts from slaughterhouses. Today, new grads benefit from displaying the picture on a monitor and the instructor showing every structure to the whole class. One disadvantage that some recent grads face is that they might have trouble pregnancy checking with just their arm, as they aren’t sure without the picture. Like everything in life, confidence comes with practice.

In conclusion, the answer to the original question, “Hey Doc, should I U/S or arm my cows?” depends on what information you are looking for and what you plan to do with it once you have gathered it.