Milk Pregnancy Test

February 26, 2013 08:37 PM
Milk Pregnancy Test

New test is accurate, convenient, affordable

A new pregnancy detection test using milk rather than blood samples is proving to be accurate, convenient, and—at $4.50 a sample—affordable.

The IDEXX Milk Pregnancy Test (MPT) is being offered as a routine service through Dairy Herd Improvement (DHI) testing centers or in customized kits of at least five samples that can then be sent directly to participating labs for analysis.

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The test measures pregnancy-associated glycoproteins (PAGs), which are released into the blood by the placenta during pregnancy and subsequently find their way into milk. Because PAGs continue to circulate in the blood stream well after calving, samples tested less than 60 days post calving can trigger false positives from the previous pregnancy.

In addition, the tests are most accurate between 35 days post breeding until dry-off, says Todd Byrem, director of AntelBio, who markets the tests.

But because of the 35 day post breeding requirement, the MPT is more of a confirmatory pregnancy test than an early detector of cows who failed to conceive. In practice, if the MPT is used with routine, monthly DHI sampling, the date of the sample might be a week or more later than 35 days post breeding on average.

Conversely, blood pregnancy tests are highly accurate, finding open cows 28 or 29 days post breeding. That allows producers to resynchronize these cows at least a full week sooner than if they rely on the MPT.

The MPT is also very accurate, but no analytical test is 100% perfect, says Paul Fricke, a University of Wisconsin (UW) reproductive specialist. "An independent study conducted by Stephen LeBlanc resulted in a sensitivity of 99.2%, which would be less than one pregnancy [missed] per 100 pregnant animals tested," he says.

Competitors point out that even this high level of accuracy can be costly, however, since resynchronizing an animal that is already pregnant will lead to an abortion.

Using the UW’s online tool, "Economic Value of a Dairy Cow," a pregnancy loss for a cow between one and two months pregnant ranges from $170 to $260, depending on when the cow became pregnant (lactation number and days after calving), says Victor Cabrera, a UW Extension specialist in dairy management.

"However, considering only the cost of the abortion is not fair for the test because the test is also helping to identify those true, non-pregnant cows that can start their resynchronization sooner," he says.

In a systematic analysis, Cabrera and Fricke found that if a pregnancy test has about a 96% accuracy (identifying true positives and true negatives), the test would still be worthwhile because of the extra gains of having cows re-enrolled earlier in the reproductive program.

In addition to having that accuracy, the MPT has the added convenience of not having to lock up cows, draw blood and submit samples. It can be done routinely through DHI sampling.

It can also be used as a simple confirmation of pregnancy test at dry-off to ensure no open cows are housed in the dry pen.

Currently, NorthStar DHI, Eastern Wisconsin DHIC and Lancaster DHI offer the Milk Pregnancy Test. Other Midwest DHIs are expected to offer the service this spring.

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