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Study seeks new understanding of how mastitis is caused

Mastitis, a highly prevalent dairy cow disease, strikes fear in the hearts of many farmers. The udder infections it entails can ruin cows’ health and productivity, wreak economic havoc on farms worldwide, and cost the dairy industry billions of dollars per year.

Now with nearly $500,000 over three years from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, faculty at Cornell’s College of Veterinary Medicine will employ a new technology that is revolutionizing bacteriology to examine mastitis in ways it has never been studied before.

“Mastitis is the most important disease in dairy cows,” said principal investigator Dr. Rodrigo Bicalho, assistant professor of dairy production medicine. “Our study will use techniques that were not available until very recently to learn more about mastitis than previously possible. We expect that our results will change perceptions of clinical mastitis, leading to reevaluation of treatment and prevention strategies.”

Finding the culprits causing mastitis once required culture techniques that isolated and grew bacterial strains in the lab. But this could only find bacteria that grow in oxygenated environments (aerobic). It could not find an aerobic bacteria, which grow in the absence of oxygen or bacteria that researchers don’t know how to culture (which is 99 percent of all bacterial species). Thus, it was long assumed that mastitis was caused by a single bacterial species growing in the mammary gland and that healthy milk was bacteria-free.

Dr. Bicalho’s lab was the first to prove that wrong in 2012. Using microbial metagenomics, which extracts and sequences DNA from all cells in a milk sample, his lab showed a whole new world of anaerobic and aerobic bacteria inside the mammary glands of both healthy and diseased cows. This opened the door to the possibility that mastitis can be caused by a combination of several different species of bacteria simultaneously.

In the new study, Dr. Bicalho will use metagenomics to target a fingerprint-like gene called 16s-rRna. Each bacterium has one to 15 copies of these genes, which contain valuable information that can identify species. Dr. Bicalho’s team will use this gene to analyze the DNA of bacteria and measure the relative proportion of each species of bacteria present.

This study will use similar techniques to explore the newly discovered bacterial world in milk and how it relates to mastitis. Dr. Bicalho and his team will collect samples before, during and after cows contract mastitis. This will let them map the baseline bacterial ecosystem of normal milk, see the disturbance in that ecosystem when a mastitis-causing pathogen arises, note any other opportunistic pathogens that come in during infection, and observe how bacterial populations return to normal if infection passes.

Major aims of the study include improving the prudent use of appropriate antibiotics and refining metagenomics techniques into new tools to diagnose mastitis and predict prognoses. To measure how the curative power of various antibiotics relates to the bacteria present, Dr. Bicalho and his team will take milk samples from cows in the field that have contracted mastitis before they treat with antibiotics. They will take follow-up samples from those cows over time to measure the extent and timing of recovery.

“This study has huge potential for developing new understanding of how mastitis is caused,” said Dr. Bicalho. “We are developing ways to use new metagenomics technology to better diagnose and treat this devastating disease that will help reduce its health risks and economic burdens.”

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