What is the heat stress? 
The cow heat stress is a bad influence caused to the cow due to heat accumulation in the cow body. Like people, cows are warm-blooded animal, the body temperature shall always remain unchanged! 

If the climate is hot, its body temperature will rise, when it feels uncomfortable, then the cow brain will issue the first instruction to make more bloods into the skin and conduct the heat exchange to take the heat out. 

If this kind of way is not enough to lower the body temperature, then the cow will start to breath heavily, if it is still not enough, then the cow will reduce the food consumption to decrease the heat of digestive system. (the cow eats little, so the milk yield will also fall off to make the falling of body temperature) 

Because multiple comprehensive factors cause that the cow heat generation is more than the heat dissipating capacity, the heat accumulation will cause the cow gets heatstroke and even death, all the above different levels of adverse heat responses generated by the cow in the different temperatures are referred to as the heat stress. 

Humidity-temperature index 
The influence of environment on heat stress of cows shall consider temperature and humidity at the same time 
Humidity index 
The above table is the influence of the cow heat stress in the different temperature and humidity. In accordance with the latest study in the United States, the threshold value of heat stress has decreased from 72 to 68, when the temperature and humidity index does not reach 68, then the mile yield and reproductive performance will reduce. 

Short-term influence of heat stress on the cow 
Respiration rate 
Increase of rectal temperature 
Increase of water consumption 
Sweating 
Decrease of feed emptying rate 
Decrease of dry matter intake 
Decrease of blood flow volume in the internal organs 
Decrease of milk yield 

Long-term influence of heat stress on the cow 
Influence on the future milk yield ?
Lower peak yield 

Breed？ 
Poor reproductive performance 

Health 
Breast health     Hoof disease 

Importance of heat stress on the pasture 
For some pastures, in case of not taking such measures, then the milk yield of the high-yielding cow may reduce 20%, the pregnancy rate will also reduce 20%. 
If the cooling effect is good, the milk yield can only reduce 2%, if daily yield of a cow is 30kg, then the difference under the cooling measure and non-cooling measure will be 6kg and 0.6kg. 
Therefore, a cow can additionally produce 5.4kg of milk through the spray cooling system, the milk yield is the most direct factor to respond cooling system effect. 

What are the main methods adopted for the cow cooling?

Cowhouse environmental cooling

Cow body direct cooling

Applicable to hot and dry environment

Applicable to hot and humid environment

Spray

Along with the increase of the cow heat stress, the cow body surface is mainly based on the evaporative heat loss

Cowhouse shade
Planting trees in pasture

Fan and spraying 

Fan spraying main points 
1g of water can take the heat of 0.578 kcal in the gas state on the cow leather, the surrounding air starts to get wet when the moisture evaporation meets a certain degree, this makes the moisture evaporate very difficult, Finally, it's like an effect in a sauna, so we need to use the fan to blow away the moist air, the combination of spraying and blowing can reach a cooling effect. The water drops shall be larger and have momentum in the spraying process, they can be ensured to fall on the cow skin, not only to be hung on the cowhair. The automatic control shall be necessary to maximize water conservation. 

Fan spraying operation mode 
Nozzle specifications used in the milking waiting hall: 500L/h, 120-180L/h nozzle of cowhouse feeding area. 
Two kinds of nozzles can spray for 30 seconds, then stop the spray and start air blow for 4.5 minutes, such a cycle has 5 minutes 
The milking waiting hall generally needs 6-8 cycles, namely 30-40 minutes, after the cows return to the feeding area, it also needs to continue the cycle of "Spraying -- Blowing", the more the better, each cow should have at least 5-8 hours every day to enjoy the cooling. 
How to calculate 5-8 hours? For example, in case of three times of milking a day, then the cow will stay in the milking waiting hall three time a day with a total of cooling time of 90-120 minutes, the cooling in the milking waiting hall can not reach 5-8 hours, so the cooling must be implemented in the feeding area and other places. 
Fan speed: The most unfavorable wind speed should reach 3m/s.