A dairy farmer loses an average of 10 to 25% of milk production during warm summer periods due to heat stress. With a herd of 100 cows, the financial damage quickly adds up to thousands of euros per season — and that’s without factoring in the hidden costs. In this article, we answer the most frequently asked questions about heat stress in dairy cattle and what you as a farmer can concretely do about it.
How much milk do cows lose due to heat stress each summer?
During heat stress, cows produce an average of 10 to 25% less milk, depending on the severity and duration of the heat. When the temperature-humidity index (THI) remains above 68 for extended periods, milk production drops noticeably. A high-producing cow yielding 35 liters per day can lose 4 to 8 liters per day.
This decline is not random. In high temperatures, a cow deliberately reduces her feed intake to generate less body heat. Less dry matter in the ration means less energy, and therefore less milk. At the same time, the fat content and protein content of the milk decrease, putting the milk price under pressure as well. Two losses in one blow.
Moreover, milk production does not always fully recover after a heat wave. Cows that experienced severe heat stress during the dry period or early lactation consistently perform worse in the subsequent lactation. The damage is therefore not limited to the summer itself.
What are the hidden costs of heat stress in dairy cattle?
Beyond the direct loss in milk yield, heat stress in dairy cattle brings a range of hidden costs that significantly increase the total damage. Think of reduced fertility, higher veterinary costs, poorer hoof health, and increased culling rates. These costs often only become visible on the farm’s balance sheet after the fact.
The most significant hidden cost items are:
- Fertility problems: Heat disrupts the hormonal balance. Signs of estrus become less visible, conception rates decline, and embryos are more vulnerable. More repeat breedings and longer calving intervals directly cost money.
- Higher somatic cell counts and mastitis: The combination of stress and heat lowers immune resistance. Mastitis occurs more frequently in summer, resulting in higher veterinary costs and milk losses.
- Reduced feed intake: Cows eat less and more selectively in the heat. This leads to rumen disturbances, acidosis, and hoof problems that can still be felt months later.
- Higher replacement costs: Cows that consistently underperform after a tough summer are culled earlier more often. A replacement heifer can easily cost 1,500 to 2,500 euros.
- Energy costs for cooling: Fans, cooling systems, and sprinkler systems consume electricity. These are real costs that need to be accounted for.
How do you calculate the total financial damage per farm?
The total financial damage caused by heat stress in dairy cattle is calculated by combining the direct milk loss with the hidden costs per cow, multiplied by herd size. A simple calculation quickly reveals just how significant the impact really is.
Use the following steps:
- Determine the average milk loss per cow per day: Based on historical production data, estimate how many liters per cow per day are lost during heat waves. Use an average of 4 to 6 liters per day for moderate heat stress.
- Calculate the number of heat stress days per summer: In Belgium and the Netherlands, this averages 20 to 40 days per year, but that number is rising. Also factor in the recovery period following a heat wave.
- Multiply by the milk price and herd size: At a milk price of €0.40 per liter, a loss of 5 liters per day, 30 heat stress days, and a herd of 100 cows, you already arrive at €6,000 in pure milk loss.
- Add the hidden costs: Taking fertility, veterinary costs, and early culling into account, experts estimate the total damage per cow per year at €200 to €400. For a herd of 100 cows, that amounts to €20,000 to €40,000 per summer.
- Compare with the cost of preventive measures: Only once you know the total damage can you properly assess whether an investment in prevention is worthwhile.
A betaine calculator or ROI tool can help make these figures concrete for your specific farm situation.
When does heat stress in cows start to become noticeable?
Heat stress in cows begins to become noticeable from a temperature-humidity index (THI) of 68. This corresponds to an outdoor temperature of approximately 24 to 26 degrees Celsius at average humidity. High-producing cows are already more sensitive at a THI between 60 and 68.
The THI combines temperature and humidity into a single figure. A warm but dry day can be less taxing than a slightly cooler but humid day. Farmers who rely solely on the thermometer therefore regularly underestimate the risk.
Early signs of heat stress include:
- Increased respiratory rate (more than 60 breaths per minute)
- Cows standing more and lying down less (to dissipate heat through the legs)
- Reduced feed intake, especially during the day
- Increased water consumption
- Visible sweating and panting
Important to know: nighttime temperature plays a major role. Cows that do not cool down sufficiently overnight start the next day with an already elevated body temperature. Warm nights are therefore at least as harmful as warm days.
Which measures reduce the costs of heat stress the most?
The most effective measures against heat stress in dairy cattle are good ventilation, adequate shade, optimal water supply, and nutritional adjustments. Combining these four pillars can significantly limit the drop in production and the associated costs.
Ventilation and cooling are the most direct interventions. Fans positioned above the cubicles and feed alley lower the effective temperature by 4 to 6 degrees. Sprinkler systems combined with ventilation are even more effective, but require a larger investment.
At the nutritional level, targeted interventions are also possible. Betaine, a natural ingredient derived from sugar beets, plays a proven role in this regard. It acts as an osmolyte: it protects cells against dehydration and stress by maintaining the osmotic balance within the cell. Scientific research shows that betaine supports dry matter intake in ruminants and positively influences rumen fermentation, even under heat stress. More information about betaine in animal nutrition provides a clear picture of the mechanisms involved.
Additional nutritional measures include:
- Adjusting the ration: more energy per kg of dry matter, less crude fiber that generates heat during digestion
- Shifting feeding times to the cooler evening and nighttime hours
- Refilling the feed fence more frequently to stimulate feed intake
- Providing sufficient fresh drinking water, preferably at multiple locations
- Using electrolytes and supportive drinking water products during extreme heat
Products administered via drinking water are particularly practical during heat stress. Water intake is more reliable than feed intake under stress conditions, meaning active substances are absorbed more consistently. Browse the range of drinking water and feed additives for dairy cattle for concrete options.
How is the risk of heat stress evolving due to climate change?
Due to climate change, the risk of heat stress in dairy cattle in Western Europe is structurally increasing. The number of days with a THI above the critical threshold of 68 rises with each decade. What was once an exceptional summer is becoming the new normal. Farmers who do not invest in prevention now will pay a higher price in the future.
By 2026, heat stress in dairy cattle in Belgium and the Netherlands will no longer be a seasonal issue but a structural business risk. Summers are becoming longer, warmer, and drier, while nighttime temperatures are rising. This means cows have less time to recover and the cumulative stress over a summer is increasing.
High-producing cows are the most vulnerable. Through selection for milk production, modern dairy cows generate more body heat per day than their predecessors. The higher the production, the faster the critical THI threshold is reached and the greater the loss when it is exceeded.
For dairy farmers, this means that heat stress management is becoming a structural part of farm operations. Investments in barn ventilation, nutritional strategy, and THI monitoring are no longer a luxury, but a necessary safeguard for long-term farm profitability.
How Jodoco helps with heat stress in dairy cattle
At Jodoco, we develop scientifically substantiated solutions that help dairy farmers and their partners structurally limit the damage caused by heat stress. Our approach combines multiple mechanisms of action in a single formula, tailored to the specific needs of dairy cattle during warm periods.
Our products for dairy cattle during heat stress offer:
- Osmotic cell support: Natural betaine protects cells against dehydration and stress, supporting dry matter intake and maintaining rumen fermentation.
- Energy support: Acibet G combines betaine with glycerol and organic acids to support energy balance and improve liver function, even during periods of reduced feed intake.
- TMR stabilization: Acibet TMR prevents the ration from heating up and keeps feed palatable for longer, promoting feed intake during hot weather.
- Flexible administration via drinking water: Our drinking water products are easy to apply and are reliably absorbed, even when feed intake declines.
- Custom formulations: We work together with compound feed manufacturers and distributors to develop solutions that fit the specific ration and farm situation.
Want to know what heat stress is really costing your farm or your customers, and how our products can reduce that loss? Contact us for a personal consultation or a tailored calculation.
