Heat stress can be fatal to livestock within a few hours, especially at extreme temperatures above 40°C. Animals that can no longer regulate their body temperature enter a life-threatening state in which their organs begin to fail. How quickly this happens depends on the animal species, the ambient temperature, humidity, and the availability of water and shade. In this article, we answer the most frequently asked questions about heat stress in livestock: from dangerous threshold temperatures to specific preventive measures.
At what temperature does heat stress become dangerous for livestock?
Heat stress in livestock can occur at lower temperatures than most livestock producers expect. For dairy cows, a temperature-humidity index (THI) above 68 is considered critical, a level that is already reached at approximately 22°C and high humidity. Pigs experience heat stress at ambient temperatures above 25°C, while poultry experience it as early as 27 to 28°C.
The dangerous thresholds therefore vary significantly by animal species:
- Dairy cows and lactating cows: THI above 68 (approximately 22°C with high humidity); severe stress at THI above 80
- Pigs and sows: stress begins at 25°C; life-threatening conditions occur at temperatures above 35 to 38°C
- Broiler chickens and laying hens: stress begins at 27 to 28°C; critical above 35°C
- Weaned piglets: more sensitive than finishing pigs; risk already present at 28°C
It is important to note that humidity has a significant impact on the perceived temperature. A barn at 28°C with 80% humidity is more dangerous for a chicken than 32°C in dry air. Livestock farmers who only pay attention to the thermometer often underestimate the actual risk.
How quickly do the symptoms of heat stress worsen?
Symptoms of heat stress in livestock can develop within one to four hours, ranging from mild restlessness to life-threatening hyperthermia. Under extreme conditions, such as a sudden heat wave combined with poor ventilation, an animal can reach a critical condition within as little as two hours.
Heat stress typically progresses in stages:
- Early stage (first 1 to 2 hours): increased respiratory rate, restlessness, reduced feed intake, increased water intake, and seeking shade or cooler areas
- Acute phase (2 to 6 hours): panting, excessive salivation, elevated body temperature (above 39.5°C in cows, above 40°C in pigs), reduced activity
- Severe stage (6 to 12 hours without intervention): muscle cramps, coordination problems, dehydration, circulatory problems
- Critical phase: organ failure, unconsciousness, and death
In poultry, this process occurs more rapidly than in large ruminants, because chickens lack a sweat gland system and rely entirely on panting to dissipate heat. If ventilation in a chicken coop fails, mass mortality and significant losses can occur within just a few hours.
Which animals are most vulnerable to heat stress?
High-producing animals are the most vulnerable to heat stress because their metabolism generates more heat than that of low-producing animals. High-producing dairy cows, heavily muscled broiler chickens, and high-producing lactating sows are at the greatest risk in hot conditions.
Specific at-risk groups include:
- High-yielding dairy cows: fermentation in the rumen continuously generates heat; at high production levels, the cows’ own heat production is enormous
- Pregnant and lactating sows: their metabolic load is already high, which significantly reduces their heat tolerance
- Fast-growing broiler chickens: their rapid growth is accompanied by a high metabolic rate and, as a result, increased body heat
- Older laying hens: their ability to regulate body temperature decreases with age
- Obese or overweight animals: Adipose tissue insulates and impedes heat dissipation
Animals that are already weakened by illness, diarrhea, or poor intestinal health are also particularly vulnerable. A damaged intestinal wall impairs fluid absorption and osmotic balance, making it harder for the animal to compensate for heat.
What are the economic consequences of heat stress at the farm level?
Heat stress causes significant economic losses at the farm level, even when there is no mortality. Losses due to reduced production, poorer reproductive performance, and higher culling rates can quickly amount to thousands of euros per summer for a medium-sized farm.
The economic impact is far-reaching and affects multiple business units simultaneously:
In dairy cattle, milk production drops noticeably as soon as the THI rises above the critical threshold. Furthermore, the decrease in feed intake leads to a negative energy balance, which negatively affects fertility and the quality of the next lactation. Cows that are bred in the summer have lower conception rates, which impacts annual planning.
In pigs, heat stress results in lower daily weight gain, poorer feed conversion, and, in sows, fewer live-born piglets. Scientific research shows that heat stress during late gestation negatively affects placental growth and the birth weight of piglets. In poultry, egg production and shell strength decline in laying hens, while broilers exhibit lower carcass weight and increased drip loss.
In addition to direct production losses, there are also indirect costs: higher veterinary expenses, additional labor for emergency cooling, and, in the worst-case scenario, the loss of animals and the associated costs of purchasing replacements.
How does betaine help reduce heat stress in livestock?
Betaine reduces heat stress in livestock by acting as an osmolyt: it protects cells from dehydration and shrinkage at high temperatures, thereby maintaining cellular function. At the same time, betaine acts as a methyl donor and antioxidant, which reduces metabolic stress during heat stress and protects intestinal integrity.
The mechanism behind this effect is straightforward. When animals experience heat stress, cells lose fluid and enter a state of osmotic stress. Betaine accumulates in the cell as a compatible osmolite without disrupting normal cellular processes. This stabilizes cellular hydration and reduces the negative effects of overheating at the tissue level.
Research on broiler chickens (Elsherbeni et al., Journal of Thermal Biology, 2025) shows that betaine improves breast muscle weight under heat stress through enhanced cellular hydration and antioxidant protection. In pigs, the effects are most pronounced in fast-growing animals and in sows during summer breeding and late gestation. In ruminants, betaine supports osmotic balance and stimulates microbial protein synthesis in the rumen, even when heat reduces feed intake.
For more information on how betaine functions as an osmolyt and methyl donor, visit our page on betaine in animal feed.
What preventive measures reduce the risk of heat stress?
You can reduce the risk of heat stress in livestock through a combination of barn management, water supply, dietary adjustments, and targeted supplementation. No single measure is sufficient on its own; a multi-layered approach is most effective.
The most important preventive measures are:
- Ventilation and cooling: ensure adequate airflow in the barn; for poultry, tunnel ventilation and misting systems have proven to be effective
- Shade and insulation: Limit direct sunlight on roofs and side walls; a white or reflective roof coating noticeably lowers the barn temperature
- Water supply: Increase the number of watering stations and monitor the water temperature; animals that drink less are more likely to experience heat stress
- Feed Management: Feed the animals in the early morning and late evening when temperatures are lower; avoid large amounts of fermentable starch, which produces excess heat
- Dietary supplements: betaine, vitamin C, and electrolytes added to drinking water support osmotic balance and the immune system during heat stress
- Monitoring: Track the THI daily and take action as soon as the threshold value is reached—not only once symptoms appear
For poultry, water intake during heat stress is a more reliable indicator than feed intake. Drinking water additives therefore offer a practical advantage: the dosage is fully controllable and intake is guaranteed, even when animals are eating less. Explore our range of drinking water and feed additives for an overview of the available solutions.
How Jodoco helps with heat stress in livestock
We develop scientifically backed feed and drinking water products specifically designed to support animals during heat stress. Our approach combines multiple mechanisms of action into a single formula, providing livestock producers and distributors with a comprehensive solution.
What we offer for heat stress prevention and treatment:
- Jodobet: natural betaine as an osmolyt and methyl donor; protects cells against heat stress, improves intestinal integrity, and supports performance in hot conditions
- Jodoplume: a liquid blend of betaine and organic acids for administration via drinking water, ideal for heat stress or coccidiosis
- Pure C Beta: Vitamin C combined with betaine for enhanced immunity and optimal hydration during heat stress
- Holistic Formulas: Our products combine betaine, organic acids, butyrate, MCFAs, and yeast cell walls to provide multi-layered protection for gut health and osmotic balance
Our products are developed in our own laboratories and validated through collaboration with national and international research institutions. Whether you’re a feed manufacturer, distributor, or professional livestock farmer, we’re happy to work with you to determine the best approach for your business. Please contact us to schedule a personalized consultation.
