THI Calculator

Ruminants: calculate the THI index to assess the risk of thermal stress

In the event of thermal stress, ruminants suffer a lower feed intake, and their dairy and reproductive performances decline rapidly. Adding Bicar®Z to the rations during hot periods is essential to obtain a BACA level of 300 and 350 mEq / Kg of MS to compensate the animal’s physiological losses. 

How can the risk of thermal stress be assessed? 

More important than the outdoor temperature itself, the atmospheric temperature and humidity are a basic index used to measure potential heat stroke in animals.

Solvay has developed a THI – Temperature - Humidity Index calculator – enabling the risk of thermal stress to be assessed instantly. 


THI = (1,8 x T + 32) - ((0,55 -0,0055 x HR) x (1,8 x T - 26))

T = temperature in °C and HR = relative humidity

This calculator is for information purposes only

If the THI is ≥72 (25°C and 50% relative humidity), then thermal stress occurs. In this case, 250 to 300g of Bicar®Z should be added to the ration.

Impact of the Temperature-humidity Index on ruminant reproduction   

>73Sudden drop in fertility
>72Thermal stress
>55Start of decrease in fertility
≤41Maximum fertility