Moderate heat is enough to trigger signs of inflammation and coagulation in dairy cows
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Climate change is transforming livestock farming—and at a faster rate than many anticipate. More frequent and intense heat waves place a heavy physiological strain on dairy cows.
Scientists at the Research Institute for Farm Animal Biology (FBN) have demonstrated that even moderate heat stress causes measurable changes in the blood of Holstein cows. These include signs of inflammatory processes and the activation of blood clotting. The findings are published in the journal Frontiers in Immunology.
At the same time, certain defense mechanisms in peripheral blood mononuclear cells (PBMCs) are suppressed. These effects were already evident after just seven days of heat stress and provide veterinarians and dairy farmers with concrete indicators for recognizing and counteracting heat stress at an early stage.
"When cows are affected by the heat, their entire organism reacts," explains Dr. Franziska Koch from the FBN. "Changes in the blood, a weakened immune system and early signs of coagulation can reduce the animals' performance and increase their susceptibility to disease. The fact that these processes begin even at moderate temperatures highlights the importance of consistent heat management in the barn."
Under these environmental conditions, the researchers found bacterial components (endotoxins from Gram-negative bacteria) in the blood, and the concentration of these components rose as heat stress increased. At the same time, the body's immune system responded by triggering inflammatory processes to remove these foreign components from the blood.
However, certain defense pathways—which are usually important for a targeted adaptive immune response—were suppressed. Furthermore, the low number of blood platelets indicated an activated coagulation cascade—a finding that was previously observed only in cases of severe heat stress with a fatal outcome.
Dairy cows naturally produce a large amount of heat. When it is warm outside, their bodies find it difficult to dissipate this heat and activate cooling processes. This can temporarily increase the permeability of the intestinal barrier, allowing endotoxins to enter the bloodstream and trigger inflammatory processes.
The new data show that this process begins even in moderate heat. In terms of day-to-day operations on dairy farms, this means taking countermeasures earlier and improving the barn environment. This can be achieved by shifting watering and feeding times to cooler periods of the day and keeping a close eye on water and feed intake by dairy cows.
For veterinary interventions, it may be important to check blood clotting in individual cases in the laboratory to better assess the animal's physiological condition.
Holstein dairy cows were studied under controlled conditions of moderate heat stress (THI 76, approximately 28°C [82°F]) for seven days. Immune responses and coagulation markers were measured over time in blood samples taken at regular intervals. These results provide valuable insights for effective heat management in barns, as well as for veterinary practice.
The temperature-humidity index (THI) is a parameter that combines temperature and relative humidity. It is used in dairy cows to estimate the threshold for heat stress.
- For lactating dairy cows, a THI of around 68 is already considered the threshold for heat stress, at which point the first negative signs appear.
- A THI of 76 corresponds to approximately 28°C (82°F) with medium humidity and indicates moderate heat stress.
- A THI >78 leads to increased heat stress with negative effects on animal health and milk yield.
Publication details
Franziska Koch et al, Dynamic immune and molecular responses to chronic heat stress in blood and peripheral blood mononuclear cells of dairy cows, Frontiers in Immunology (2025). DOI: 10.3389/fimmu.2025.1633453
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Citation: Moderate heat is enough to trigger signs of inflammation and coagulation in dairy cows (2026, July 14) retrieved 14 July 2026 from https://phys.org/news/2026-07-moderate-trigger-inflammation-coagulation-dairy.html
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