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Heat Stress in Dairy Cattle
2002-12-01

Abstract

Heat stress is a major limiting factor to milk production in tropical and subtropical Asia

Dairy Production in a Hot Climate

The production of milk is directly related to the level of feed consumption. Dairy cattle under high-temperature conditions have a lower feed intake than those which 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 animal to get rid of excess body heat.

Cows suffering from heat stress also show a change in their hormones. One study in Hawaii showed that cattle kept without any shade had a lower level of estrogen than those with access to 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!!

In August, FFTC held a training course in heat stress in dairy cattle. The course was held in Taiwan, which in August is suffering from sweltering temperatures of well over 30oC, with high humidity. Trainees were able to visit small-scale dairy farmson this subtropical island, as well as some larger dairy units, and see what is being done to keep the herds cool.

The training course had several objectives:

  • To discuss the effect of heat stress on the production and reproduction of dairy cattle;
  • To introduce effective methods of modifying the temperatures on smallholder dairy farms.

How to Reduce Heat Stress

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 environmental control for their housing. A range of technologies are needed, to match the different economic and other needs of smallholders.

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 cow's body temperature as close as possible to the normal (between 38.5oC and 39.3oC).

Evaporative cooling can be accomplished by two approaches:

  • Direct evaporation from the skin surface of the cows; and,
  • Indirect evaporation. This involves cooling the micro-environment of the cows with cooling pads and fans in an enclosed barn.

In hot and humid subtropical regions, evaporative cooling always requires the use of forced ventilation.

Sprinklers without fans, or fans without sprinklers, will not give an effective cooling system.

A combination of fans, wetting, shade and well-designed housing can help alleviate the negative impact of high temperatures on dairy cows in the tropics. Careful milking management, feeding strategies and sensitivity to animal behavior are also important in achieving efficient milk production in tropical dairy herds.

Some Dairy Farms in Taiwan

Farms in Taiwan are small. A typical dairy farm has a herd of 100-150 cows and is run by a husband and wife team, sometimes with one or two helpers.

Taiwan is located in the subtropics, with high summer temperatures and humidity. Dairy cattle exposed to such an adverse environment are likely to have reduced milk production and breeding performance.

A method of cooling the cows has been developed. They are repeatedly wet with a water spray. Their coats are then dried by rapid evaporation, using forced ventilation. Results show that the use of this cooling system can alleviate heat stress in dairy cows. It improves their thermal balance, and their productive and reproductive performance.

Index of Images

Figure 1 Well-Designed Shed for Tropical Dairy Herd Provides Shade and Good Ventilation

Figure 1 Well-Designed Shed for Tropical Dairy Herd Provides Shade and Good Ventilation

Figure 2 Water Spray Used in Taiwan to Cool Dairy Cows

Figure 2 Water Spray Used in Taiwan to Cool Dairy Cows

Figure 3 Dairy Cows Cooled by Fans

Figure 3 Dairy Cows Cooled by Fans