Heat stress is a condition where there is a marginal increase in temperature thereby leading to an increase in air temperature, reduction of air movement and relative humidity. Whenever the ambient temperatures increase, a cow’s body temperature also increase which also leads to an increase in respiratory rate, salivation and water consumption, indicating noticeable discomfort.
A drop in dry matter intake (DMI), milk yield and milk fat production, and impaired reproductive performance. Heat stress also has a negative effect on dry cows and heifers, there are physiological changes are connected to heat stress in dairy cows.
This usually leads to huge economic loss especially in livestock business and usually cause setback to farmers, the following are the causes:
- It reduces heifer feed coversion ratio thereby leading to poor growth rates;
- Disruption in feeding and feeding pattern;
- Panting and increased drooling;
- It can lead to rumen acidosis;
- It can lead to reduced feed intakes and reduced rumination;
- It lead to reduced milk yield;
- Change in milk composition, e.g. fat % and protein % declines;
- Poor reproductive performance;
- Increased cost of production;
- Lameness and sudden loss of animals.
However, cow breeds can tolerate heat stress differently and researches have shown that high milk producing cows are more likely to exhibit signs of heat stress than low milk producing cows because they produce more heat as they consume more feed for higher levels of production.
Heat Stress Management
There is a need for dairy farmers to prepare adequately for the hot seasons in order to prevent huge economic losses that could happen and the following are ways to manage heat stress:
- Provide clean and adequate water at all times, lactating cows will require
more than 100 litres/cow/day and will drink between two to six times per day;
- Provision of shade for the animals, painting of metal roofs white or aluminum and adding insulation aids in reflecting solar radiation helps to insulate animals from thermal radiation;
- Providing fans and sprinklers to help cool the cows;
- Avoid overcrowding by increasing spacing;
- Provide ruminal digestible protein source;
- Maintain the standard fibre level in animals diet;
- Feed good quality forages to animals for high digestibility;
- Increase minerals such as sodium, potasium and magnesium;
- The ration fed to cows in hot weather should be balanced properly for minerals. There is a need to increase potassium to 1.3 to 1.5 percent, sodium to 0.5 to 0.6 percent, and magnesium to 0.3 to 0.4 percent may result in less heat stress by allowing the animals to dissipate heat.
- Farmers should not overfeed highly degrable protein, i.e. 65 percent or greater degradable crude protein in the rumen, because this also increases the heat increment and requires more heat to be dissipated from the animal. Proper supplementation of more undegradable protein will be effective in reducing the heat of digestion.