THI - Heat Comfort Measurement
The Temperature-Humidity Index (THI) is an objective measure of animal heat load.
What is THI?
THI (Temperature-Humidity Index) is a composite indicator that expresses the combined effect of environmental temperature and relative humidity. It is one of the most widely used tools for assessing animal thermal comfort.
High temperature alone does not necessarily cause heat stress, but combined with humidity it significantly limits animals' heat dissipation capacity, especially the efficiency of evaporative cooling.
THI Formula
T = temperature (°C), RH = relative humidity (%)
THI Threshold Levels
| Level | THI | Ruminants | Swine | Poultry |
|---|---|---|---|---|
| Normal | < 68 | |||
| Mild stress | 68 - 72 | |||
| Moderate stress | 72 - 80 | |||
| Severe stress | > 80 |
Limited Heat Dissipation
At high humidity, animals cannot effectively dissipate excess heat through evaporation. The efficiency of skin surface and respiratory evaporation decreases, body temperature begins to rise, and signs of heat stress appear.
Supplementary Parameters
Solar Radiation
Direct solar radiation significantly increases heat load, especially for pasture-kept animals.
Convection
Air heat transfer through the animal's body surface, depending on environmental temperature and air flow.
Wind Speed
Air movement facilitates heat dissipation, making ventilation crucial in enclosed barns.
Corrected THI for Ruminants
The corrected THI developed for ruminants also takes into account solar radiation and wind speed, providing a more accurate picture of actual heat load. This is particularly important for pasture-kept herds, where the classical THI may underestimate actual stress.
ThermoTool Application
The CCPA ThermoTool mobile application provides real-time THI monitoring and alerts, helping farmers take preventive measures in time.