Cows struggle more with heat than humans because they have a much higher metabolic heat production, are less efficient at sweating, and combine a large body volume with relatively little skin surface area. Dairy cows also generate enormous amounts of body energy through their intensive milk production, which creates additional heat. In this article, we answer the most frequently asked questions about heat stress in cows, from the physiological causes to practical solutions for the livestock farmer.
What makes a cow’s body temperature so vulnerable to heat?
A cow’s body temperature is vulnerable to heat because cows naturally have a high metabolic heat production. An adult dairy cow continuously generates large amounts of body heat through digestion, rumen fermentation, and milk production. As ambient temperature rises, dissipating that heat becomes increasingly difficult.
In humans, normal body temperature is approximately 37°C. In cows, it is slightly higher, around 38.5°C. But the difference lies not so much in the target temperature as in the amount of heat the animal produces itself. A high-producing dairy cow generates up to three times more metabolic heat through rumen fermentation and milk production than a comparably sized, non-productive animal.
Added to this, cows have an unfavorable ratio of body volume to skin surface area. The larger the animal, the harder it is to shed heat through the skin. Humans are relatively small and have a large skin surface area relative to their body mass, which facilitates heat dissipation. In cows, that ratio works in exactly the opposite way.
How do cows cool themselves down, and why is it less effective than in humans?
Cows cool themselves through respiration, radiation, conduction, and limited sweat secretion. The primary cooling mechanism in cows is panting, in which moist air is rapidly exhaled to carry heat away. However, this is considerably less efficient than sweating in humans, especially at high humidity.
Humans have millions of sweat glands distributed across the entire body. During exertion or heat, humans can secrete up to several liters of fluid per hour, producing a powerful cooling effect through evaporation on the skin. Cows do have sweat glands, but they are limited in number and capacity. They produce relatively little sweat, which means evaporative cooling plays a secondary role.
Panting also consumes energy in itself, generating additional heat. Furthermore, rapid panting leads to a loss of carbon dioxide, which disrupts the acidity of the blood. This can result in respiratory alkalosis, a condition in which the blood becomes too alkaline, with negative consequences for digestion and mineral balance.
At high humidity, evaporation is barely effective — whether through the skin or through breathing. This makes the combination of heat and humidity particularly dangerous for cows, while humans in similar conditions also suffer but are better able to cool down through intensive sweating.
At what temperature is heat stress in cows considered to begin?
Heat stress in cows occurs when the Temperature Humidity Index (THI) exceeds 68. This index combines temperature and humidity. At a dry ambient temperature of approximately 25°C and a relative humidity of 50%, that threshold is already reached. High-producing dairy cows begin to feel the effects at an even lower THI.
The THI is a better measure than temperature alone, because humidity strongly affects the effectiveness of evaporative cooling. A cow may still function reasonably well at 28°C with low humidity, but at 25°C and 80% humidity she may already show clear signs of stress.
Researchers generally distinguish four levels of heat stress:
- No stress (THI below 68): The cow functions normally; production and health are unaffected.
- Mild stress (THI 68–72): First signs of increased respiratory rate and a slight decrease in feed intake.
- Moderate stress (THI 72–80): Noticeable decline in milk production, reduced fertility, and elevated body temperature.
- Severe stress (THI above 80): Risk to health, significantly increased risk of heat stroke and mortality.
It is important to note that high-producing dairy cows are more susceptible than low-producing animals or dry cows. The more milk a cow produces, the more metabolic heat she generates and the sooner she enters the danger zone.
What are the consequences of heat stress for milk production and animal health?
Heat stress in cows leads to a measurable decline in milk production, poorer reproductive performance, and increased susceptibility to infections and metabolic disorders. The effects are not limited to the hot period itself but can persist for weeks to months after temperatures return to normal.
The most immediate consequences are:
- Reduced feed intake: Cows eat less to limit heat production from digestion, leading to a negative energy balance.
- Drop in milk production: Lower energy intake translates directly into less milk. Depending on the severity of the stress, this can amount to several liters per cow per day.
- Poorer milk quality: The fat and protein content of the milk decreases, which is financially detrimental to the farmer.
- Reduced fertility: Heat stress disrupts the hormonal cycle, decreases estrus expression, and reduces embryonic survival.
- Increased risk of mastitis and hoof problems: Compromised immunity and altered lying behavior increase the risk of udder infections and lameness.
- Osmotic stress at the cellular level: Cells lose moisture due to heat, which damages cell integrity and metabolism.
Osmotic stress at the cellular level is an aspect that is often underestimated in practice. When cells become dehydrated due to heat, this has direct consequences for the intestinal barrier, liver function, and immunity. Betaine, as a natural osmolyte, plays an important role in protecting cells against this type of stress by helping to retain moisture within the cell without disrupting normal cell function.
How can livestock farmers reduce heat stress in cows?
Livestock farmers can reduce heat stress in cows through a combination of housing management, dietary adjustments, and targeted supplementation. No single measure is sufficient on its own, but together they can significantly limit the impact of heat and protect the production and health of the herd.
In terms of housing and environmental management, the following measures are effective:
- Ensure adequate ventilation through fans or naturally ventilated barns with open sidewalls.
- Use misting systems or sprinkler installations to lower the air temperature inside the barn.
- Always provide fresh, cool drinking water at multiple locations throughout the barn. Water intake increases significantly in hot weather.
- Adjust feeding times: provide the largest portion of the ration in the early morning or late evening, when it is cooler.
- Limit transport and other stressful activities to the coolest hours of the day.
Dietary adjustments also play an important role. It is worthwhile to increase the energy density of the ration without disrupting the fiber balance, so that the cow needs to eat less while still taking in sufficient energy. Products that support rumen fermentation and help offset the negative energy balance are particularly valuable during this period. Our Acibet G is a good example: it combines betaine, glycerol, and organic acids to support liver function and stimulate feed intake.
Drinking water is a particularly effective delivery vehicle for supplemental nutrients during heat stress. Water intake during stress is more reliable than feed intake, and dosing is fully flexible and controllable. This makes it easier to provide cows with the right support even during difficult periods.
How Jodoco helps with heat stress in cows
Heat stress is a complex challenge in which multiple physiological processes come under pressure simultaneously. For more than 25 years, Jodoco has been developing scientifically grounded solutions based on natural betaine, precisely for situations like these. Betaine acts as an osmolyte: it protects cells against dehydration and stress, supports metabolism as a methyl donor, and helps keep the intestinal barrier intact, even at high temperatures.
Our approach to heat stress in dairy cattle includes:
- Cellular protection through betaine: Betaine retains moisture within the cell and reduces osmotic stress, directly counteracting the effects of heat at the cellular level.
- Support for energy balance: Products such as Acibet G and Ruval help offset the negative energy balance that arises from reduced feed intake during heat.
- Maintaining gut health: Heat stress damages the intestinal barrier. Betaine strengthens tight junction proteins and protects the intestinal wall, contributing to better nutrient utilization even during warm periods.
- Flexible administration via drinking water or feed: Our products are available in liquid and dry form, allowing the farmer to choose what best suits the situation on their farm.
Would you like to know which solution best fits your herd and farming operation? Contact us and we will be happy to work with you on a targeted approach to heat stress in your cows.
