Heat stress in livestock is measured by assessing the combination of temperature and humidity using the Temperature Humidity Index (THI), supplemented by direct observation of the animals’ behavior and physiological signs. Starting at a THI of 68, cows begin to noticeably suffer from the heat, while pigs and poultry are even more sensitive. In this article, we answer the most frequently asked questions about recognizing, measuring, and addressing heat stress in livestock barns.
What are the first signs of heat stress in livestock?
The first signs of heat stress in livestock include increased respiratory rate, reduced feed intake, increased water intake, restlessness, and seeking shade or cooler areas in the barn. In cows, milk production declines early on, while pigs lie down more and are less active. These behavioral changes are often the earliest and most reliable signs.
The specific signs vary slightly by animal species. In dairy cows, a sudden drop in milk production is one of the first measurable effects. At the same time, you’ll notice that cows breathe more frequently and more deeply, sometimes with their mouths open and their tongues hanging out. They also spend more time standing rather than lying down, because body heat is better dissipated into the air when they’re standing.
In pigs, and especially in sows in late gestation, heat stress manifests as reduced feed intake and an increased risk of fertility problems. Scientific research shows that heat stress in the summer can significantly affect reproductive performance. In poultry, you’ll notice that the birds start panting, spread their wings, and eat less.
- Increased respiratory rate and panting
- Reduced feed intake, increased water intake
- Declining milk production in cows
- Restlessness, or conversely, apathy and spending more time lying down
- Spreading Wings in Poultry
- Reproductive Disorders in Sows and Cows
The sooner you recognize these signs, the faster you can take action and minimize production losses. Early detection is therefore just as important as the measurement itself.
What is the Temperature-Humidity Index, and how does it work?
The Temperature Humidity Index (THI) is a combined measure that takes into account both air temperature and relative humidity to calculate the heat stress on livestock. The THI better reflects how harsh conditions are for animals than temperature alone, because high humidity hinders heat dissipation through evaporation.
The basic formula for THI is: THI = (1.8 × T + 32) – (0.55 – 0.0055 × RH) × (1.8 × T – 26), where T is the temperature in degrees Celsius and RH is the relative humidity in percent. Some software and online calculators use simplified versions of this formula, but the principle remains the same.
The thresholds used in practice are:
- THI below 68: No significant risk of heat stress for dairy cows
- THI 68 to 72: Mild heat stress; slight drop in production possible
- THI 72 to 80: Moderate heat stress, clear impact on production and welfare
- THI 80 to 90: Severe heat stress, increased risk of health problems
- THI above 90: Very severe heat stress, risk of death
Pigs and poultry are affected even at lower THI values. For pigs, a threshold of around 22 to 25 degrees Celsius at normal humidity is already considered critical, regardless of the formal THI calculation. In practice, the THI has been most extensively developed for cattle, but the underlying principle of combined temperature and humidity applies to all livestock kept in barns.
How do you accurately measure the THI in the barn?
To accurately measure the THI in the barn, you need a calibrated thermometer and a hygrometer that record both temperature and relative humidity. Combination sensors that measure both values simultaneously and display them digitally are the most practical. Placing them at animal height, at multiple points throughout the barn, provides the most representative picture.
The placement of the sensors determines the reliability of the measurement. A sensor that is mounted too high or too close to a fan will provide a distorted picture of what the animal is actually experiencing. Mount sensors at the height where the animals are located: for cows, at a height of approximately 1 to 1.2 meters; for pigs, closer to the floor.
In larger barns, it is advisable to select multiple measurement points, especially if there is uneven ventilation or sunlight coming through windows and skylights. Corner areas and spots close to the exterior wall can be significantly warmer or more humid than the barn average.
Modern data loggers automatically record measurements and make it possible to track trends throughout the day and night. This is valuable because heat stress can persist even at night if the barn does not cool down sufficiently. A cumulative picture over 24 hours provides more insight than a peak value recorded at the hottest time of the day.
What methods are available for measuring heat stress in livestock?
There are three main methods for measuring heat stress in livestock: environmental monitoring using THI sensors, physiological measurements taken directly from the animals, and behavioral observation. In professional livestock farming, these methods are often combined to provide a comprehensive picture.
Environmental Monitoring
This is the most common method used in practice. Data loggers or smart sensors are used to continuously measure temperature and humidity at the barn floor level. Many modern systems link this data to an app or dashboard, allowing you to monitor conditions remotely and receive an alert when critical thresholds are reached. This enables you to take proactive action even before animals show visible symptoms.
Physiological measurement
Direct measurement on the animal provides additional information. A cow’s body temperature normally ranges between 38.0 and 39.3 degrees Celsius. A temperature above 39.5 degrees, combined with high ambient temperatures, is a reliable indicator of heat stress. Respiratory rate is another physiological indicator: a rate above 60 breaths per minute in cows indicates an elevated stress level. Similar indicators apply to pigs and poultry.
When does heat stress in livestock become a serious problem?
Heat stress in livestock becomes a serious problem as soon as the THI exceeds the threshold value for the species in question and this condition persists for several hours a day or for several consecutive days. A single peak stress event is less harmful than chronic exposure, which leads to a sustained decline in production, reduced fertility, and increased susceptibility to disease.
For dairy cows, the negative effects begin even with relatively mild heat stress. Research shows that even at a THI of 68 to 72, milk production decreases noticeably and feed intake declines. At higher values, embryonic mortality also increases and the quality of colostrum deteriorates.
In pigs, heat stress during the summer is a well-known cause of declining reproductive performance. Sows that are bred during the summer have a lower chance of conception and, on average, give birth to fewer live piglets. Scientific evidence, published in journals such as Animal Reproduction Science, confirms that heat stress during gestation has a direct impact on piglet production.
Of all animals kept in confinement, poultry is the most vulnerable. Broilers and laying hens quickly experience a decline in production performance even under mild heat stress: feed conversion efficiency worsens, growth slows, and in laying hens, eggshell strength decreases. In extreme cases, heat stress leads to increased mortality, resulting in direct economic losses.
What can you do once heat stress has been diagnosed?
Once heat stress has been identified, the top priorities are to improve ventilation, increase water supply, and adjust feeding times to the cooler hours of the day. In addition, nutritional interventions can help limit the physiological impact on the animal and protect its performance.
Practical steps you can take right away:
- Maximize ventilation or turn on mechanical cooling
- Ensuring there are enough cool drinking water stations
- Shift meal times to early morning and late evening
- Temporarily reduce occupancy density where possible
- Provide shade during grazing or outdoor time
In addition to these environmental measures, nutrition plays an important role. Animals under heat stress have an increased need for osmotic support, antioxidants, and specific nutrients that protect cells. Natural betaine is a proven effective substance in this regard: as an osmolyt, it helps cells retain fluid and protects the intestinal barrier during stress. Scientific research confirms that, under heat stress conditions, betaine improves the production performance of broiler chickens, including breast muscle weight and feed conversion.
Targeted solutions are available for drinking water administration that can be implemented quickly and flexibly. Drinking water additives for livestock offer a practical advantage: water intake remains more reliable than feed intake in stressed animals, ensuring that the active ingredients reach their target.
How Jodoco Helps with Heat Stress in the Barn
At Jodoco, we have been developing scientifically proven products for more than 25 years to help animals cope with heat stress. Our solutions are based on natural betaine, organic acids, and essential oils, and are specifically designed to mitigate the physiological effects of heat and protect performance.
Here’s what our approach actually achieves in cases of heat stress:
- Osmotic cell support: Betaine helps cells retain moisture and reduces epithelial stress at high temperatures
- Maintaining intestinal integrity: Our formulas strengthen the tight junctions in the intestinal wall, ensuring that the barrier function remains intact under stressful conditions
- Protection of Technical Performance: In poultry, swine, and ruminants, trials consistently show improved growth, feed conversion, and carcass quality under heat stress
- Reproductive Support: In sows and cows, betaine helps improve reproductive performance, even during hot weather
- Flexible administration: Via drinking water or feed, depending on the situation and the animal species
Our products, such as Jodoplume and Pure C Beta, have been specifically developed for use in drinking water during periods of heat or stress. They are easy to dose and can be deployed quickly as soon as the THI reaches critical levels.
Would you like to know which solution best suits your situation, animal species, or production phase? Contact us, and we’d be happy to work with you to develop a tailored approach to heat stress on your farm.
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