- Increased breathing and pulse
- Excessive drooling
- Shade seeking behavior
- Increased rectal temperature
- Increased water intake and reduced feed intake
- Dizziness and unconsciousness
During a circumstance of high ambient temperature and humidity, the animals could not alleviate their excess body through only non-evaporative measures such as conduction, convection or radiation. In such cases the animal relies on the evaporative cooling mechanisms such as sweating and panting.
The primary signs of heat stress are sweating and panting. Sweating causes when the evaporative heat loss occurs through the skin while in the case of panting, the heat is removed from the lungs by directly using the senses to heat the water vapor and removing heat in the form of vaporized moisture. The study depicts that the heat loss due to cutaneous evaporation accounts for relatively 20-30% of the total heat loss when the atmospheric temperature is between 10 – 20℃. On the other hand when the ambient temperature rises to 30℃ or higher, the heat loss through cutaneous evaporation is the only medium for about 85% of the total heat loss. Both sweating and panting becomes the source of heat loss when the air temperature equals the core body temperature where the sensible heat loss will be equal tozero.Along with the release of heat to the atmosphere, both these indicators depletes the body water reserve as well. The maximum sweating rate of dairy cows and feedlot heifers is 660g/m2/h.This leads to wastage of energy produced. Each gram of evaporated sweat utilizes about 580 calories of energy which can be utilized for productive performance.
As mentioned above the respiration rates can be used as a quick tool to assess whether the animal is in heat stress or not. The respiration rate exceeding 80 breaths per minute clearly indicates the sign of heat stress.
Studies report that when a cow is exposed to 850 W/m2 of solar load for three hours, the rectal temperature rises to 40℃ or greater. Also the respiration rate rises above 124 breaths/min.During such instances dark skinned cows immediately show signs like sticking of the tongue outside the mouth, drooling and foaming. Instant actions are needed during such stages. Immediate spraying of water on the body helps to alleviate heat stress up to a certain limit.