Have you been at the end of your rope when dealing with a respiratory outbreak, a nutritional meltdown or a series of fatal calf scours, and then, as a last resort, decide to run some diagnostic tests? If you answered yes to any part of this question, have the results been too late, too costly or provided the wrong information? If so, there may be newer technologies and better strategies to help with this dilemma. When the need for diagnostic testing arises, dairy producers have a variety of tests available, some of which are outlined here.

Screening tests
Screening tests are proactive and should be considered as a necessary “finger on the pulse” in determining the health status of your dairy. Some may not be specific enough to determine the disease status of an individual animal but can be used to assess the existence and prevalence of a disease or condition, or assess the presence of risk factors that may lead to trouble down the road.

There are many benefits to screening tests. They provide risk mitigation, enable producers to track disease trends and may pinpoint the introduction of a disease. They are highly sensitive and yet can be rather inexpensive.

There are many examples of screening tests on the dairy that are not directly involved in disease diagnostics, such as screening for antibiotic residues, colostrum quality and serum protein in calves to detect failure of passive transfer of antibodies from colostrum. Nutritionists also routinely use screening tests to monitor molds and aflatoxins.

Screening tests for animal-disease diagnostics include ear notching and milk and fecal pooling for presence of bovine viral diarrhea (BVD), Mycoplasma and Johne’s, respectively.

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Another BVD screening test is string sampling, which is the collection of milk samples from separate milking strings. A screening test used commonly by nutritionists to monitor protein utilization is the milk urea nitrogen (MUN) test. Johne’s disease also can be screened with a milk ELISA test, which limits animal handling and is much more convenient than blood and fecal tests. The sensitivity of the milk tests is comparable to its serum counterparts.

In the future, watch for milk screening tests for progesterone or other measure of estrus in the cow. This test can be used to assess reproductive health and nutrition, as well as to evaluate employee compliance of reproductive synchronization programs.

Individual tests
“Traditional diagnostics” often evokes the idea of individual tests. Two examples of individual diagnostics are a milk culture from a hot mastitis case or a necropsy of a cow that died suddenly without an obvious cause. Individual tests may be used in diagnosing mastitis, bovine respiratory disease (BRD), diarrhea or a sudden unexplained death.

These tests are highly sensitive, specific and helpful in making decisions on individual cows. However, there is a time lapse in receiving laboratory results, the tests are expensive, and they may not be relative or predictive to the herd in general. If we know the cause of death of one cow out of a thousand in a herd, how helpful is this? With a little creativity, though, these tests can be modified to provide information that is more useful.

Individual tests that are convenient, fast and economical are cow-side tests. Both producers and veterinarians can utilize this technology to provide quick data on a variety of health indicators. Using milk or blood samples, the tests provide a quick screening for things such as calcium, phosphorus, ketones, progesterone, magnesium and somatic cell counts. Cow-side tests are popular for screening milk fever, ketosis, estrus, pregnancy and mastitis. The results are not as conclusive as other types of tests, but the results are more immediate, as the samples do not have to be submitted to a laboratory.

A new technology being used in the U.S., Europe and Israel is “in-line” milk testing. It tests for diseases like Mycoplasma, BVD and ketosis, as well as progesterone for estrus detection. The tests are quick, easy and effective, but the technology is expensive and the results are difficult to interpret.

A progesterone study in Denmark detected 99 percent of the animals were diagnosed pregnant by traditional palpation, making this as reliable as any other method of pregnancy diagnosis. The biggest challenge with this new technology is distilling the amount of information to a practical and useable form. With more time and experience, in-line milk testing likely will become more widely adopted and practical.

Multiple individual tests
Reaching a level of statistical significance in your diagnostics program provides a higher level of disease detection and allows you to more successfully respond to herd-health challenges. A significant number of tests provides a more comprehensive approach and increases the likelihood of identifying disease because of a higher quantity of tests and higher-quality results. This approach is more labor-intensive and expensive, but worth the investment if the end-result is quick and accurate disease diagnosis.

For example, if you have a mastitis outbreak, you can take multiple milk cultures to more confidently identify and respond to the cause of infection. If you’re seeing an increase in displaced abomasums or retained placentas, your cows could have subclinical milk fever (hypocalcemia). You can determine if this is causing the problem by measuring blood calcium levels using cow-side samples from a group of fresh cows.

Dr. Don Sockett at the Wisconsin Veterinary Diagnostic Laboratory has developed a new method for testing BRD in calves. Deep-pharyngeal swabs provide a truer sample and are less invasive than other methods. They also allow you to determine the respiratory pathogens and sensitivities to antibiotics when your calves are alive and still treatable – a huge advantage.

Combination tests
Combining screening and individual tests could be the right approach for diagnosing disease in some situations. For example, consider a group of 200 animals. After taking individual BVD ear-notch samples, the lab pools the samples into batches of 25, and run tests on the eight pools. If the test is positive, you have the capability to test the individual samples.

If the test is negative, there’s no reason to run additional tests. Because the samples are averaged together, the results may be less sensitive, but the efficiency and economic benefit makes combination testing a legitimate option. Some debate the economic advantages of routine testing for BVD, but what is not debatable is the havoc a couple of undetected persistently infected BVD animals can wreak on a herd’s reproductive performance.

Using diagnostic testing properly will help producers increase their herd health parameters. As you continue to tackle the tough choices of what to use and what to throw away in this prolonged economic downturn, do not forget to look at proactive diagnostics. They provide “real-time” results and actually may save – rather than cost – money. PD

Michael Bolton