Reduce Costs with On-Farm Milk Culturing Techniques

By Blake Jackson

Not every case of mastitis in dairy cows requires treatment. Sometimes a cow’s immune system has already cleared the infection, making antibiotics unnecessary. On-farm culturing helps producers make informed treatment decisions by identifying whether an infection truly needs intervention and which quarters require attention.

Mastitis is the leading reason for antibiotic use in dairy cows. Treatment costs, combined with lost milk due to withdrawal, can exceed $350 per cow annually. Yet antibiotics are often overused or ineffective, which not only reduces farm profitability but also increases the risk of antibiotic resistance.

Identifying the specific bacteria causing mastitis allows producers to target treatments, avoid unnecessary antibiotics, and adjust management practices to prevent future infections. For example, Staphylococcus aureus is spread during milking, and controlling it involves glove use, teat dipping, and milking infected cows last. Studies show that 10-40% of clinical mastitis cases may have no bacterial growth, indicating that treatment is not needed.

Traditional lab cultures can take several days, delaying decision-making and increasing costs. On-farm culturing offers a faster, more cost-effective alternative. Penn State has developed a quad plate system to identify common mastitis pathogens.

The plate includes MacConkey Agar for Gram-negative bacteria, Edwards Modified Agar for Streptococci, Baird Parker Agar for Staphylococci, and Blood Agar to confirm results. Producers need sterile test tubes, swabs, plates, and a temperature-controlled incubator. Milk is plated aseptically, incubated for 24-48 hours, and then assessed for bacterial growth.

On-farm culture can’t detect all bacteria, such as Mycoplasma bovis, which requires lab conditions. However, it allows producers to identify self-cured cows, Gram-negative pathogens that may not need treatment, and Gram-positive bacteria responsive to antibiotics. Treatment decisions should consider the cow’s udder health history and involve veterinary guidance.

Penn State Extension offers the online course “On-Farm Milk Culturing for Mastitis Control.” For more information, contact Ginger Fenton at gdc3@psu.edu.

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