A cow cools itself through a combination of evaporation, conduction, convection, and radiation. In practice, sweating and panting are the most visible mechanisms: cows release moisture through the skin and breathe faster to dissipate heat. Because cows sweat less efficiently than humans, they are more susceptible to high temperatures. In this article, we answer the most frequently asked questions about heat stress in dairy cows, from the underlying physiology to practical solutions for the barn and the ration.
What mechanisms does a cow use to regulate her body temperature?
A cow regulates her body temperature through four physiological mechanisms: evaporation (sweating and panting), conduction (heat transfer through direct contact with cooler surfaces), convection (heat dissipation through airflow across the skin), and radiation (heat release to the surrounding environment). Evaporation is the most effective mechanism at high temperatures, but cows have fewer sweat glands than humans, which limits their cooling capacity.
As ambient temperature rises, a cow automatically increases her respiratory rate. While a healthy cow at rest breathes roughly 20 to 40 times per minute, this can climb to more than 80 breaths per minute under heat stress. This panting accelerates the evaporation of moisture through the airways and helps the animal shed excess heat.
At the same time, cows seek out shade, reduce their movement, and stand still more often. They drink more water to maintain fluid balance and may position themselves near ventilation sources to benefit from convection. All of these behavioral adaptations are instinctive responses aimed at keeping the internal body temperature — normally around 38.5 degrees Celsius — stable.
What is heat stress in cows and when does it occur?
Heat stress in cows occurs when an animal’s heat production exceeds its ability to dissipate that heat to the environment, causing body temperature to rise above the comfortable range. This happens when the temperature-humidity index (THI) reaches a value of 68 or higher — a combination of temperature and humidity that impairs the cow’s ability to cool down.
The THI combines temperature and relative humidity into a single figure. A hot but dry day can be less taxing than a slightly cooler but humid day, because high humidity inhibits evaporative cooling through sweating and panting. Dairy cows are particularly sensitive: due to their high metabolic rate, they generate substantial body heat internally, even at moderate outdoor temperatures.
High-producing cows, pregnant cows in the final weeks before calving, and cows in early lactation are the most vulnerable. Their metabolic activity is so high that they can already experience heat stress at temperatures around 25 degrees Celsius when humidity is elevated.
How does heat stress affect milk production and cow health?
Heat stress in cows demonstrably leads to reduced milk production, decreased feed intake, impaired fertility, and a weakened immune system. Even a limited period of heat stress can cause milk production to drop by 10 to 25 percent, depending on the severity and duration of the heat.
Effect on milk production and feed intake
When a cow experiences heat stress, she reduces her feed intake as a direct response to generate less metabolic heat. This has an immediate impact on energy balance and, consequently, on milk production. Cows in early lactation — who are already in a negative energy balance — are hit twice as hard: they have a harder time compensating for energy deficits.
In addition, the composition of the milk changes. Fat content and protein content decline, putting pressure on quality premiums for dairy farmers. Lactation persistency — how long a cow maintains a stable level of production — also decreases when periods of heat stress recur.
Effect on fertility and immunity
Heat stress disrupts hormonal balance and suppresses ovulation. Signs of estrus become less visible, conception rates decline, and early embryonic mortality increases. Farmers notice this through longer calving intervals and lower pregnancy rates during the summer months.
The immune system also functions less effectively under heat stress. Cows become more susceptible to mastitis, hoof problems, and other infections. The intestinal barrier can weaken, increasing the risk of leaky gut and secondary inflammation. All of this raises veterinary costs and reduces farm profitability.
What practical measures reduce heat stress in the barn?
Practical barn measures to combat heat stress in cows focus on three principles: cooling the air, improving air circulation, and reducing the heat load in the environment. A combination of ventilation, cooling, and shade delivers the best results.
The most effective measures at a glance:
- Improve ventilation: Ensure adequate airflow throughout the barn through ridge vents, open sidewalls, or mechanical fans. A minimum air speed of 1 to 2 meters per second at cow level noticeably reduces heat load.
- Cooling with water: Misting systems or drip cooling applied to the cow’s back lower skin temperature through evaporation. This works best in combination with ventilation.
- Provide shade: Shade is essential both in the pasture and in the holding area before milking. Cows without access to shade have significantly higher body temperatures.
- Optimize drinking water supply: Cows under heat stress drink two to three times more water. Ensure sufficient drinking stations, large water troughs, and a constant supply of fresh, cool water.
- Reduce stocking density: More space per animal reduces mutual heat production and gives each cow greater access to ventilation and drinking water.
- Adjust milking times: Milk preferably in the early morning and late evening, when temperatures are lower.
Barn design plays a role in the longer term. A well-designed freestall barn with an open ridge, wide side openings, and an east-west orientation makes maximum use of natural airflow and prevents unnecessary heat accumulation.
What dietary adjustments help cows cope better with heat?
Dietary adjustments during heat stress focus on compensating for reduced feed intake, replenishing losses caused by sweating, and supporting metabolism. The key is to offer more energy-dense feed, replace electrolyte losses, and deploy specific nutrients that strengthen heat tolerance.
A number of targeted adjustments farmers can apply:
- Increase the energy density of the ration: Because cows eat less, they need to take in more energy per kilogram of dry matter. Add more rumen-protected fat or energy-rich by-products to the ration.
- Feed more frequently in smaller portions: More frequent feeding stimulates intake and reduces peak rumen fermentation, which itself also generates heat.
- Replenish electrolytes: Cows lose potassium, sodium, and magnesium through sweating. Supplementation via the ration or drinking water supports osmotic balance and reduces the effects of dehydration.
- Use betaine as an osmolyte: Natural betaine helps cells maintain their fluid balance under heat stress. Betaine acts as an osmolyte: it protects cells from shrinkage caused by moisture loss and thereby supports cellular function at high temperatures. In ruminants, betaine also supports microbial protein synthesis in the rumen and the production of short-chain fatty acids.
- Include buffers in the ration: Sodium bicarbonate and other buffers stabilize rumen pH, which is more frequently disrupted during heat stress because cows ruminate less.
Feeding timing also matters. Provide the largest portion of the ration during the cooler evening hours, so that peak fermentation — and the associated heat production — falls outside the hottest part of the day.
When is heat stress in cows a serious problem in Belgium and the Netherlands?
In Belgium and the Netherlands, heat stress in cows is a real risk from May through September, with the greatest likelihood of problems occurring in July and August. Although the climate in the Low Countries is temperate, heat waves with temperatures above 30 degrees Celsius have become more frequent and more intense in recent years.
The critical threshold for dairy cows is a THI of 68, which corresponds to approximately 24 degrees Celsius at a relative humidity of 70 percent. During recent summers, both countries recorded multiple days with THI values above 72 or even 80 — conditions that represent severe heat stress for high-producing cows.
What makes the problem particularly urgent in this region is the combination of factors at play. Many traditional barns were built without climate control. The high production levels of modern dairy cows come with high metabolic heat output. And summers are getting warmer: what was once an exceptional heat wave is increasingly becoming normal summer weather. Farmers who invest now in ventilation, cooling, and dietary adjustments are protecting not only their animals but also their long-term business results.
How Jodoco helps with heat stress in cows
At Jodoco, we have spent the past 25 years specializing in solutions based on natural betaine — precisely because betaine plays such a powerful role in protecting animals against stress, including heat stress. Our approach for dairy farmers combines multiple modes of action in carefully developed formulas.
What we offer for cows under heat stress:
- Acibet G: A liquid source of betaine, glycerol, isomaltulose, and organic acids that stimulates feed intake, supports liver function, and reduces negative energy balance. Trial results show that cows receiving 300 grams of Acibet G per day maintain their milk production with 25 percent less concentrate feed per 100 kilograms of milk.
- Acibet TMR: Prevents heating of the TMR ration, keeps feed fresher and more palatable for longer, and improves feed intake — especially during the warm summer months when feed spoilage poses an added risk.
- Glycoboost: Supports energy balance through natural betaine, rapidly available carbohydrates, and glycerol. Prevents fatty liver and ketosis, which occur more frequently following periods of stress.
- Drinking water additives: Because water intake is more reliable than feed intake during heat stress, we offer solutions for administration via drinking water, with full dosing flexibility for the farmer.
Our products are scientifically substantiated, developed in our own laboratories, and tested in collaboration with knowledge institutions both domestically and internationally. Want to find out which approach best fits your farm situation? Contact us and we will be happy to think it through with you.
