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PAG is shorthand for
Pregnancy-Associated Glycoproteins

Alertys is a range of cow pregnancy tests from IDEXX, designed to make pregnancy detection simpler and easier, without the need for invasive internal examination of each animal.


The tests detect specific proteins, present in blood or milk, called pregnancy-associated proteins (PAGs). PAGs are only produced in the embryonic regions of the placenta. Unlike progesterone, a hormone that occurs in peaks and troughs during a cow’s reproductive cycle, PAGs are only expressed when the cow is in-calf.


The specificity of PAG production, and its detection in milk or blood samples, makes any Alertys test an accurate and efficient method of pregnancy diagnosis.

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PAG evolution after insemination: example of a pregnant cow

Based on the graph, it shows that anything below 0.10 is classified as negative and anything above 0.25 is classified as positive. Between 0.10 and 0.25 is classified in the recheck zone. 


Generally, PAG levels rise steeply after 21 days or 3 weeks of pregnancy. The Alertys tests are validated from 28 days and as seen from this graph at this stage, the PAG level is above the cut-off level of 0.25.

Therefore, it is recommended that the test is used from day 28 post insemination to avoid false negatives.

PAG evolution after embryonic loss: example of an embryonic loss at 35 days

PAG levels in a cow don’t go straight back to zero after embryonic loss. It takes time for the levels to decline. 

From this graph you can see how PAG falls after an embryonic loss at day 35.


PAG begins to fall immediately, and rapidly, but it is likely to take 6-10 days to recover a negative result. If, after 28 days post service, a cow returns a result in the “re-check zone”, a failed early pregnancy is a likely reason for this low, but detectable PAG level.

embryonic loss after 35 days.jpeg

PAG evolution after full-term calving

After calving, PAG levels fall quite sharply initially, and then a slight levelling off. On average, the levels are below 0.25 (the positive cut-off) by 30 days after calving.


However, as with all biological tests, there is some variability around the mean. In order to be confident that detected PAG levels are not from a previous pregnancy, the standard advice with this test is not to use it for pregnancy diagnosis within 60 days of the previous calving

pag evolution after calving.png

Alertys tests cannot predict the stage of pregnancy

This figure describes the results from a large Danish study of nearly 300,000 milk-recorded pregnant cows, using the IDEXX Alertys Milk Pregnancy test. It shows that the test continues to detect PAGs above the cut-off level of 0.25 produced by a healthy placenta from around 28 days post insemination until the end of the pregnancy.


Note that there is a slight dip in PAG levels around day 60. The test cut-off (within the red line) which is used, means that this rarely causes a problem, but around 2-3% of pregnant cows will have a result in the recheck zone during this short period.

Besides, PAG level normally rises throughout gestation for the majority of cows, but even if the tendency is to have high PAG levels at the end of gestation, it is impossible to predict the stage of pregnancy using PAG concentration.

Danish study graphic.png

Alertys PAG Testing in short:

  • Accuracy is uniform across all breeds of cow

  • Both dairy and beef farms can benefit from Alertys testing

  • Non-invasive testing is less stressful for the cow and presents zero risk for the developing foetus

  • There is no evidence to suggest that milk from antibiotic-treated cows has any negative effect on the test result

  • Milk from high-yielding cows may show lower PAG levels, but this does not affect the accuracy of test results

  • While the test is more than 99% accurate for the detection of pregnant or open cows, it cannot reveal the stage of gestation, the sex of the calf, or if the cow is carrying multiple calves

  • The accuracy of PAG testing supports earlier and more informed decision-making which, when combined with appropriate veterinary input, can improve whole-herd health and management strategies

  • Alertys is not a replacement for veterinary input in managing your herd’s reproductive performance. Instead, Alertys allows to identify cows that can benefit from the Vet’s knowledge and expertise in applying more focused, individual attention to optimise their reproductive performance.


Want to find out for yourself how Alertys can improve herd performance, welfare and productivity? 

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