Table 2.

Effect of heat stress on dairy cattle.

THI	Stress level	Effects
22.2°C (< 72°F)	None
22.2–26.1°C (72–79°F)	Mild	Dairy cows will adjust by seeking shade, increasing respiration rate and dilation of the blood vessels. The effect on milk production will be minimal.
26.6–31.6°C (80–89°F)	Moderate	Both saliva production and respiration rate will increase. Feed intake may be depressed and water consumption will increase. There will be an increase in body temperature. Milk production and reproduction will be decreased.
32.2–36.6°C (90–98°F)	Severe	Cows will become very much uncomfortable due to high body temperature, rapid respiration (panting) and excessive saliva production. Milk production and reproduction will be markedly decreased.
>36.6°C (>98°F)	Danger	Potential cow deaths can occur.

THI, temperature humidity index. Adapted from Samal (33).