Temperature Humidity Index (THI) Calculator
Use this calculator to help manage heat stress in cows.
The information needed to calculate Temperature and Humidity can be obtained free from the MetService (www.metservice.co.nz).
Enter the Temperature and Relative Humidity information in the appropriate box below and click the "Calculate" button. The Temperature Humidity Index is then calculated.
| Temperature (°Celsius) | |
| Relative Humidity (%) | |
Temperature Humidity Index: |
Note: This calculator uses the following formula:
THI= (1.8xT+32) - ((0.55-0.0055xRH) x (1.8xT-26)) Where T=Temperature and RH=Relative Humidity
Production Impacts
When THI reaches 68 for Friesians and 75 for Jerseys (equivalent to 21 and 25.5°C respectively at 75% relative humidity) New Zealand cows begin to experience the effects of heat stress. This is seen by a reduction in feed intake and a drop of around 10g milksolids per day per unit increase in THI (Bryant et al. 2007).
For example, an increase in THI from 68-78 would equate to a 100g drop in milksolids/cow/day. Note that a drop in fat/protein percentage occurs before a drop in yield or milksolids is visible (Bryant et al. 2007).
- For more information see FarmFact 3-15 Managing Heat Stress in Cows
