Hot environments affect the performance of dairy cows both directly and indirectly. To attain the fullest genetic performance, environmental conditions and diets should be modified.
Thermal factors consist of air temperature, humidity, air movement, and radiation rate. In lactation Holstein cows, the comfortable temperature is within the range 4-24⁰C.
The effects of heat stress on the cows begin to be observed above 24⁰C, and milk yield decreases markedly above 27⁰C.
A decline in milk yield, fertility, and growth rate in hot environments is closely related to an increase in body temperature.
Preventing an increase in body temperature in hot environments can be approached in three ways, by lowering the environmental temperature by modifying the structure of the shed where the cattle are kept, or by introducing cooling facilities.
Farmers can also increase heat stress by sprinkling them with water, using fans and so on.
Also, they can increase the efficiency of feed energy utilisation, and reducing the heat increment of animals from feeding.
Careful management that can alleviate heat stress in the best way to maintain high production levels in lactating cows in a hot environment.
Good management includes the modification of the surrounding environment to reduce the impact of the environment and or to promote heat loss from the animals.
Simple shade is the basic method in summer of protecting animals from direct solar radiation during the day.
The most effective source of shade are tress and other plants. They provide not only protection from sunlight, but also create a cooling effects through the evaporation of moisture from their leaves.
Shade has a beneficial effect on the physiological response of dairy cattle to heat.
Although air temperature and the level of solar radiation begin to fall after about 2pm, the temperature of the roof remains high.
As a result, the body temperature and respiration rate both rises and night grazing can be an option.
The production of milk is directly related to the level of feed consumption and also dairy cattle under high temperature conditions have a lower feed intake than cows that are kept cool.
A major part of feed digestion in ruminants consists of fermentation in the rumen, as microbes work on digesting fiber and other ingredients.
This produces a tremendous amount of heat. The warmer the environment, the more difficult it is for the animals to get rid of excess body heat.
Cows suffering from heat stress also show a change in their hormones. One study in Hawali showed that cattle kept without any shade had a lower level of oestrogen than cows than with access of shade. There were other hormonal changes as well, which meant that cows suffering from heat stress had a lower conception rate. And a cow without a calf is a cow without milk.
Reducing heat stress in dairy cattle requires a multi-disciplinary approach.
It involves breeding for improved heat tolerance and improved nutrition for the animals, and improved structural design and other needs of smallholder farmers.
Physical modification of the environment is based on two concepts: protecting the cows from the factors contributing to heat stress, and enhancing evaporative heat loss by the animal. The major objective of a cooling system is to reduce the air temperature inside the barn, to keep the cows’ body temperature as close as possible to the to the normal (between 38,5⁰C and 39,3⁰C)
BY GENERAL BEVEN MUNDIDA (LIVESTOCK CONSULTANT)
+263 776420161/ +263 717056597