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NorthStar DHI offers mastitis diagnostic to reduce high SCC

For DHI members, controlling contagious mastitis is now easier than ever. In response to the dairy industry’s focus on milk quality and the reduction of SCC, NorthStar DHI and AntelBio are launching next generation tools to aid producers in detecting contagious mastitis pathogens. Applied to existing DHI-collected milk samples, the new testing procedure simultaneously detects Staphylococcus aureus, Streptococcus agalactiae, and Mycoplasma spp. with greater accuracy and quicker turnaround than traditional culture.

Improved testing performance is accomplished by applying PCR technology that detects bacterial DNA, and is not dependent on the viability of bacteria in the sample. Moreover, detection in DHI collected samples offers convenience and flexibility when implementing mastitis testing protocols previously underutilized because of time and labor constraints. For producers wondering what mastitis pathogen is causing subclinical high SCC values this test can conveniently hold the key.

The new testing procedure is focused on contagious mastitis pathogens because they are a leading cause of subclinical, high SCC and in contrast to the environmental pathogens, their presence in DHI-collected milk samples is more directly attributable to udder infection than environmental contamination. Contagious pathogens (S. aureus, Strep. ag and Mycoplasma spp.) gain entrance to the mammary gland largely through the teat canal during milking and generally produce long-term infection that results in elevated bulk tank or herd average SCC scores.

Direct economic losses from contagious mastitis’ impact on milk production and treatment costs are frequently obvious and significant. However, the impact on milk quality and
revenues jeopardized as a result of milk antibiotic residues, manufacturing and nutritional quality issues, while more difficult to quantify, are no less important.

While several mastitis testing strategies can be designed for routine DHI test dates, the most commonly used testing protocol is expected to be high SCC cow testing. Since chronic, unresponsive high SCC is mainly associated with infection by contagious pathogens, focused testing on high SCC DHI milk samples can be used routinely to identify individually infected cows.

Using SCC data from the DHI Hot Sheet, milk samples above preselected thresholds can be saved at the lab and tested on the PCR test panel. Thresholds can be based on fixed SCC values (e.g., 200,000; 500,000; 750,000) or simply an absolute number of cows with the highest SCC scores (e.g, top 20; 10; 5 cows). Cows infected with contagious mastitis pathogens act as reservoirs for continued transmission and depending on the organism, immediate treatment or culling are critical to the control of contagious mastitis in the dairy herd.

In herds that have controlled contagious mastitis, routine screening programs to prevent re-introduction into the milking herd can also be developed for DHI test dates. Fresh cow testing can be used to screen, milk samples from recently fresh animals. To reduce costs, milk samples can be pooled 5-to-1 prior to analysis. For more thorough detection, it is advisable to conduct follow-up testing on individual samples from positive pools. However, for routine surveillance, testing individual samples in positive pools could be omitted until an abnormally high incidence of specific pathogens are detected.

Bulk tank testing can be the most economical way to screen dairy herds for the re-introduction of contagious mastitis pathogens. A variety of factors contribute to the determination of appropriate testing intervals, but every four weeks on scheduled DHI test dates should be considered a minimum for routine screening. Between DHI test dates, bulk tank samples can be dated and frozen, then transported to the laboratory for analysis on the subsequent DHI test day.

For more information, consult your DHI specialist on your next DHI test day or contact AntelBio at 1.800.631.3510.