The cow thermo-neutrality zone is between 10 and 20 ° C.

Figure: Thermal comfort and discomfort zones for dairy cows and calves (source: BTPL)

Above 25 ° C., you can observe:

• Alteration of physiological behavior and energy balance
• Consequences for reproduction and longevity
• Consequences on the quantity and quality of milk production

The reaction to heat stress depends on:

• Physiological characteristics (short-haired cows regulate their temperatures better)
• lactation stage and production level
• the composition of the ration and the consumption of food
• Animal building (ventilation - ventilation, etc.)

The implementation of a new agro-climatic indicator, the Temperature-Humidity Index (ITH) allows the thermal stress of the animal to be assessed by the pair "temperature, humidity". The table below presents the 5 “hygro-thermal” stress zones for cattle:

• comfort zone, in green
• stress threshold zone, in yellow (from 20 ° C. for high relative humidity)
• light to moderate stress area, orange
• zone of moderate to major stress, in dark orange (from 27 ° C. for humidity exceeding 70%)
• major stress area in red

Figure: Temperature-Humidity Index (ITH) for dairy cows (Source: FIDOCL)

Figure: Dairy cow victim of "sunburn" summer 2019 in Aubrac region