How Heat Stress Increases Mastitis Risk in Cows

By Blake Jackson

Many dairy producers notice an increase in somatic cell count (SCC) in their herds during the summer and fall. This seasonal rise is often linked to heat stress, which not only reduces milk production but also contributes to higher SCC and increased risk of environmental mastitis, according to Amber Yutzy, Assistant Director, Animal Systems Programs at Penn State Extension. Understanding why SCC increases and how to prevent it is key to maintaining herd health and profitability.

Somatic cell counts tend to rise as temperature and humidity climb. Heat stress physically strains cows, causing them to spend more time standing or seeking cooler areas rather than eating. At the same time, environmental mastitis risk increases because teats are exposed to more bacteria.

Research shows that elevated stress hormones can weaken immune response, reducing the effectiveness of somatic cells in combating infections. When bacteria enter the udder, the immune system sends somatic cells to fight them, but stress hormones can hinder this process, allowing SCC to rise.

Producers can take several steps to manage heat stress and lower SCC. Keeping bedding clean and dry reduces bacterial growth and encourages cows to rest in proper stalls. Fans and sprinklers help cool cows but should be managed carefully to avoid wet bedding or overly damp areas.

Flies are another concern, as they spread disease and increase stress; fly control helps limit mastitis transmission. Proper employee training on milking procedures ensures infections are identified quickly and new infections are minimized.

Providing abundant, fresh water is critical, as cows drink up to 50% more when temperatures reach 26.66°C versus 4.44°C. Water helps cows regulate body temperature through perspiration and respiration.

By focusing on heat stress management, maintaining clean, dry housing, and following correct milking routines, producers can reduce seasonal SCC spikes, limit mastitis, and boost overall milk production and herd profitability.

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