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Stop Heat Becoming a Stress

Heat Stress

Heat stress is not something that we usually associate with our cows in Northern Ireland. However, it is an issue that is becoming increasingly prevalent due to weather extremes and the fact that many cows are now fully housed year-round. Cows are robust animals, and they can tolerate short-term temperature/humidity levels, provided there is a quick return to comfortable levels. Generally, a temperature humidity index (THI) of over 70 is the point where heat stress becomes an issue and impact performance. An optimal temperature for dairy cows is between 5–20°C. Cows are more prone to heat stress due to the significant heat increment caused by high feed consumption and milk production. Alltech has developed a simple, no-stress guide on managing heat stress, which I will explain below.

Step 1: Be AWARE of the signs of heat stress

  • Decreased dry matter intake
  • Reduced cudding activity
  • Increased respiration rate and panting
  • Standing and congregating
  • Milk yield drop
  • Lowered milk solids
  • Higher somatic cell count (SCC)
  • Decreased oestrus levels
  • Reduced pregnancy rate


Step 2: We need to be ready to ADAPT the animals’ housing and environment

Cows need to be as comfortable as possible. The basic principles include providing increased shade, cooling and good ventilation along with ample, clean and accessible water. There will be an increase in the demand for water, so make sure water inputs can cope with this extra demand. Reduced stocking rates is another method to consider. Reduce group sizes in the collecting yard, for example. Water troughs and feed passages should be cleaned more often than usual. We need to look at the forages also. Any heated spoiled silage should be disposed of. Keeping a good clamp face is key. A well-sharpened shear grab or block cutter should help keep a tight face. Expose the clamp in smaller sections. Try and get across the pit face as soon as possible. The TMR should be not heating. Twice-a-day feeding may be another method to use. Adjust feed times to when temperatures are lower to help stimulate an intake in the cows. Feed should be pushed up 8–10 times per day also.


Step 3: Help cows ACCLIMATISE via feed and nutrition

In times of heat stress, our focus needs to be on sustaining rumen health and function. Cows in heat stress are more likely to have subacute ruminal acidosis due to the changes in their feeding behaviour. These changes are caused by fewer and larger meals resulting in slug feeding. Feeding high-quality, palatable forages during times of heat stress is another strategy for minimising digestive heat. As feed intake is depressed, we need to increase the energy density of the diet. We can do this by adding more cereals or fats. Choose starch with slower degradation rates (for example, maize meal versus barley). Mineral concentration needs to be also considered. Sodium, potassium and magnesium are also lost through salvia and sweat, so we need to take those into account too.

Feed YEA-SACC® to help stabilise rumen environment and optimise function. YEA-SACC® helps promote dry matter intake, enhances the digestibility of the diet by removing oxygen toxic to microbes and promotes digestion and utilisation of nutrients. YEA-SACC® helps to stabilise the rumen environment by stabilising rumen pH and reducing the time during which the rumen is below the critical pH of 6.

Heat stress is an issue we need to take seriously. As I mentioned earlier, it can have serious implications on performance, which will then result in reduced profitability. By using our three-step, no-stress strategy, we should be able to minimise these implications. For any further advice on keeping your dairy herd free from the effects of heat stress, please contact InTouch on 01213742969 or log on to Heat stress | Alltech.