Pregnancy Diagnosis in Cows

Pregnancy is one the most important times in the lives of dairy and beef cows. For dairy cows, a successful and well-timed pregnancy will give the best milk yield and provide replacement stock for the herd. Accurate data on pregnancy status of cattle can aid in culling decisions; breeding management and timing; and inform decisions on grouping cows for feeding, calving and serving.

So how can you tell if a cow is pregnant?

There are a number of commonly used pregnancy diagnosis (PD) methods in cattle. Some of them can only be performed by an experienced technician or vet, but some are cow-side test that a producer can take into their own hands.

Rectal palpation

Rectal palpation is a manual method of pregnancy diagnosis which has been performed for many years. A vet will insert their hand into a cow’s rectum and will feel for signs associated with pregnancy, for example a developing foetus. An experienced vet can have error rates as low as 3%,¹ so they can identify 97% of pregnancies correctly.

This method is usually performed from 30-40 days after service or AI, and then increases in accuracy over time. The same method can be used to detect problems in a cow’s reproductive system such as cystic ovarian disease, or persistent corpus luteum.

This procedure is such a well-known and reliable method of diagnosis that, as a result, it has come to be considered as a routine procedure.

Trans-rectal ultrasonography

Similarly to ultrasound scans for other animals, ultrasonography is a highly accurate and reliable form of pregnancy detection. While it was once both expensive and confined to practices with stationary equipment, with the advent of portable machines, ultrasonography has become an everyday procedure.

Vets or techs can perform reliable pregnancy detection as early as 28 days after service. Later on in the pregnancy, this method can be used to determine sex of the foetus, how far advanced the pregnancy is, and whether the cow is carrying multiples². Vets can also check ovaries and reproductive organs for problems. Ultrasound examination is extremely accurate, but requires a skilled practitioner to read.³

Progesterone Testing

While not a direct pregnancy test, progesterone testing can be used to see if a cow is not pregnant. Cows produce progesterone throughout pregnancy. So, if a test shows a low progesterone result, you can assume that the cow is not pregnant. Cows naturally have high progesterone at times in their cycle, even when not pregnant. Consequently, a high result doesn’t always mean pregnancy. As such, testing must be done 18-21 days after AI or service to get the most reliable results.

Progesterone tests are widely used for heat detection⁵. As a result, many types are commercially available. Tests can be milk dipstick tests, like P4Gold, which can be done cow-side, or can be lab-based tests. Lab tests can be done on blood or milk⁴, but need a greater level of skill and precision, and are generally more expensive. For farm-side dipstick tests, producers can get an immediate result, allowing real-time decisions on fertility management.

Pregnancy-associated Glycoprotein (PAG) Testing

The placenta produces bovine pregnancy-associated glycoproteins (PAGs) at around 25 days after service.⁶ Only animals which are pregnant or have been pregnant recently show these proteins. As a result, they are an effective measure of pregancy.⁷

There is currently no farm-side test for PAGs, but lab tests for blood and milk are available. Unfortunately, PAGs have very long half-lives in a cow’s system. This means that, even if she loses the pregnancy early on, the PAGs will still be present, so a false positive result might occur. In the same way, if the calving interval is small, leftover PAGs from the previous pregnancy might give a positive result from an empty cow. ⁷

There are many ways of detecting a pregnancy in cows. Some are more invasive than others, and they all have different degrees of accuracy. All herds are different, so the best way forward is likely a combination of methods. This depends on individual choice, availability and affordability.

References

1. Whittier, Proceedings, Applied Reproductive Strategies in Beef Cattle 15, (2013).
2. López-Gatius, et al., Livestock Science 197, 12–16 (2017).
3. Pieterse, et al., Theriogenology 33, 697–707 (1990).
4. Bulman & Lamming, British Veterinary Journal 135, 559–567 (1979).
5. Roelofs, et al., Animal Reproductive Science 91, 337–343 (2006).
6. Zoli, et al., Biology of Reproduction 46, 83–92 (1992).
7. Shahin, et al., Small Ruminant Research 113, 141–144 (2013).