Pregnancy testing in ruminants

Reproductive efficiency is a major concern for livestock producers, as it can have a significant economic impact on any livestock operation. Determining pregnancy status early on is arguably the most important factor in determining reproductive efficiency. Early identification of open (non-pregnant) females provides a better evaluation of conception rate (often related to male or semen fertility), efficacy of an artificial insemination program, and possible underlying infectious/noninfectious diseases. Females identified as open can then be rebred or inseminated, thereby providing an economic advantage to the producer. Knowing the pregnancy status of an animal is invaluable in making management decisions regarding nutrition and herd health, such as adjusting nutrition to provide for fetal demands, and administration of vaccines to prevent abortion and ensure passive transfer of immunity.

An ideal pregnancy test is one that is safe and can identify open and pregnant animals with a high degree of accuracy early after mating. There are several techniques used for pregnancy diagnosis. In ruminants, research has focused for several years on biochemical and hormonal methods to determine pregnancy status. One of these tests is the determination of the level of a group of proteins called pregnancy associated glycoproteins, or PAGs, in the blood of pregnant animals. The following are a few facts about how this test is used for pregnancy determination in ruminants.

What test does WADDL use for pregnancy determination in ruminants?

WADDL uses a commercially available and licensed enzyme-linked immunoassay Pregnancy Test Kit from IDEXX Laboratories Inc. The test detects early pregnancy-associated glycoproteins as a marker for pregnancy. The test is validated internationally for use in cattle, sheep, goats, and buffalo.

What does the test look for?

The test detects the presence of pregnancy associated glycoproteins in the blood. PAGs are a family of proteins produced by specialized cells of the developing placenta. These proteins start being produced early in pregnancy, are taken up into the dam’s blood, and can be found in serum. Although production of these proteins begins early in the period of attachment of the embryo, their concentration is not high enough for detection until day 28-35 of pregnancy, depending on the species. PAG production is maintained at a high level until the termination of pregnancy, and residual PAGs can be detected in serum for a period of time after birth.

When is the earliest I can test my animal for pregnancy?

The test is reliable in most ruminant species starting at 28 days from the last mating or artificial insemination, as long as the last birthing has taken place at least 60 days prior.

Normally, if a female is not pregnant following natural service or artificial insemination, she should come back into heat with a normal cycle (cow – 18 to 24 days; sheep – 16 to 18 days; goats – 18 to 24 days). Females not observed in heat following a mating are often presumed pregnant. However, heat detection is not always reliable and certain pathological conditions can interfere with a normal estrous cycle. Testing for PAGs is an extremely reliable method of pregnancy detection that can be used as early as 28 days after mating in cattle and goats, allowing for rebreeding of open females.

How accurate is the test?

The test is extremely accurate in determining pregnancy status if used according to the kit manufacturer’s instructions (IDEXX Ruminant Pregnancy Test). Because PAGs are produced by the placental cells, they are only produced during a pregnancy.

The sensitivity of the test (ability to detect a pregnant animal) is 99.3% in serum samples. This means that test will identify 99.3% of pregnant females.
The specificity of the test (ability to detect a non-pregnant animal) is 93.8% in serum samples. This means that the test will accurately identify 93.8% of the open females.

When can I test my sheep, goat, or cow?

We recommend testing 28 days post-breeding for cows and goats and 35 days post-breeding for sheep.

How can my animal be positive (pregnant on the test) but come back in heat or fail to show pregnancy later?

In most species, it is expected a few animals will lose their pregnancy early on. These early embryonic deaths often go unnoticed because the conceptus and its membranes are not developed enough for clinical signs of pregnancy to appear. Most of these losses occur in the first 40 days of pregnancy. Therefore, some females may test as pregnant at 30 days and either return to estrus or fail to give birth. It is always prudent to retest animals later in pregnancy to confirm their status. 

If several females present with this situation (being open following a positive pregnancy test result), it is important to consult with your veterinarian about investigating the underlying problems of pregnancy loss.

If blood samples are taken less than 60 days after parturition, they may test positive, regardless of the current pregnancy status of the animal due to residual amounts of PAGs from the previous pregnancy. This is why it is important to test no earlier than 60 days following parturition.

How can my animal test negative and now be pregnant?

If a female tested open and is determined to be pregnant later, the most common reasons would be the female was bred at a later date or the sample was taken too early.

Why is my animal testing negative but not coming back in heat?

The possibility that a female is open but is not identified by the test is extremely low but can occur. In these cases, you may choose to retest the animal. However, there are several reasons an open female will not return to estrus, including ovarian or uterine pathologies and seasonality. Consult your veterinarian if any questions arise.

Can the test tell me how many fetuses are being carried?

This test can only ascertain pregnancy status and cannot determine fetal numbers.

How often do I need to test my animals?

The frequency of testing depends on the system of management. Consult with your veterinarian to determine the frequency that is right for you.

Who can I contact for more information about pregnancy testing in ruminants?

You can also contact WADDL at 509-335-9696 or the WSU Veterinary Teaching Hospital’s Theriogenology service at 509-335-0711.

Page revised March 2024