Ask the Vet

Value of Culls and Cost of Hay Make Cow Pregnancy Checks a Good Investment

If a cow isn't going to deliver a healthy calf, it's a good year to move her out of the herd early and save on the cost of feed. (DTN/Progressive Farmer file photo by Meg McKinney)


What are the advantages and disadvantages of using a blood test to pregnancy test cows?


Years ago, many farmers "bumped a calf" to determine pregnancy. This means they would sharply push in on the cow's abdomen several times and then hold their fist firmly against the abdomen to feel the calf in the uterus as it swung back and forth. This only worked with late-term pregnancies, but it was somewhat useful to know when to dry off a milk cow to let her get ready for the next lactation.

Later, rectal palpation by a veterinarian became the gold standard of pregnancy testing. Experienced veterinarians can accurately determine pregnancy down to as little as 30 days post-breeding. Especially for up to four months, the veterinarian can give a fairly accurate estimate of fetal age. In addition, diseases, fetal mummies, and injuries that might lead to abortion or difficulty in calving can be identified. This information in real time allows for culling, treatment, and sorting decisions while the cow is still in the chute.

Beginning in the mid-1980s, ultrasound became an option. It can often detect pregnancy as early as 28 days, with some techniques reportedly decreasing that to fewer than 20 days. Ultrasound can detect fetal viability, sex, and some reproductive or developmental abnormalities. This provides a more precise determination of fetal age, and just like with rectal palpation, results are available immediately.

When properly timed, ultrasound and rectal palpation can distinguish between artificial insemination (AI) and natural service pregnancies.

Now, let's talk about blood tests. These are probably best called "biochemical tests," because some use blood and others use milk to identify hormones or proteins unique to pregnancy. These tests are reported to be 99% accurate and require sample collection. These samples are sent to a central laboratory, and results are available anywhere from a few days to a few weeks. Recently, chute-side tests have been developed for use on the farm, with results in 30 minutes or sooner.

With biochemical tests, cattle must be at least 73 to 95 days from calving (depending on the test) to avoid interference from the previous pregnancy. Abortions and early embryonic deaths can result in false positives.

In a year like this one, given the value of cull cows and the cost of feed and hay, I believe it's especially critical to preg check the cow herd. Convert the freeloaders into bottom-line profits sooner rather than later.


Editor's Note: Please contact your veterinarian with questions pertaining to the health of your herd or other animals. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice but is purely for informational purposes.

Write Dr. Ken McMillan at Ask the Vet, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email