Nighttime heat stress is more dangerous than daytime heat stress because animals cannot recover during the night from the heat load they accumulated during the day. During the day, temperatures rise, but once the sun sets, conditions normally cool down enough for the body to restore its thermal balance. When nighttime temperatures remain above critical threshold values, the body stays in a continuous state of stress, with serious consequences for production, health, and welfare. In this article, we answer the most frequently asked questions about the difference between daytime and nighttime heat stress.
Why is nighttime heat stress more dangerous than daytime stress?
Nighttime heat stress is more dangerous than daytime stress because the night is normally the recovery period for animals. During the day, animals can temporarily compensate for heat load, but without a cool night, physiological stress accumulates. This cumulative effect leads to a chronic burden that structurally undermines production, fertility, and immune resilience.
During the day, animals respond to heat by eating less, drinking more, panting more, and reducing their activity. These are normal adaptations that temporarily protect the body. However, the damage only becomes truly critical when body temperature fails to drop at night. The body cannot repay its thermal debt, meaning the following day begins with an already elevated core temperature.
In poultry, pigs, and cattle, it has been shown that nighttime temperature is a stronger predictor of production losses than peak daytime temperature. A warm night of 24 degrees Celsius can cause more damage than a hot day of 32 degrees, simply because the recovery window is absent. Farmers who monitor only daytime temperatures therefore systematically underestimate the actual heat stress load their animals are experiencing.
How does nighttime heat stress affect animal production?
Nighttime heat stress reduces feed intake, disrupts hormonal balance, and increases the maintenance requirements of animals, directly leading to lower growth rates, reduced milk production, and poorer reproductive outcomes. Because recovery does not occur, the production consequences of nighttime heat stress are disproportionately large relative to the temperature increase alone.
In dairy cattle, persistent nighttime heat leads to a measurable decline in milk yield and a deterioration in milk composition. The energy balance is disrupted because the animal expends more energy regulating body temperature while feed intake simultaneously decreases. In sows, the effects are particularly visible during summer breeding: nighttime heat stress reduces embryonic survival and lowers the number of piglets born alive.
In poultry, the feed conversion ratio (FCR) deteriorates significantly when nights remain warm. Broilers use a greater proportion of their energy intake for thermoregulation rather than muscle growth. This results in lower breast muscle weight, a higher fat percentage, and increased mortality. Laying hens show a decline in egg production and weaker eggshell strength, particularly when warm nights occur on consecutive days.
What are the signs of heat stress during the day versus at night?
Daytime heat stress is visible and immediately observable, while nighttime heat stress manifests insidiously through production declines and behavioral changes that only become apparent the following day or later. The difference in signal timing makes nighttime heat stress harder to recognize and therefore more dangerous in practice.
Signs of daytime heat stress
- Increased respiratory rate and panting
- Reduced feed intake, particularly during the warmest hours of the day
- Animals seeking shade or clustering near ventilation openings
- Increased water intake
- Reduced activity and social interaction
- Visible lethargy in poultry (wings spread, beak open)
Signs of nighttime heat stress
- Reduced feed intake the following morning, even when the day starts cool
- Restless behavior at night — animals not lying quietly
- Elevated core temperature when checked early in the morning
- Persistently elevated respiratory rate even after sunset
- Gradual production decline over multiple days without a clear daily peak
- In sows: irregular estrus cycles or reduced conception rates following warm periods
The key distinction is that daytime stress is acute and visible, while nighttime stress is chronic and hidden. Farmers who only monitor during the day therefore miss a significant portion of the actual load their animals are carrying.
When does nighttime heat stress become a real risk?
Nighttime heat stress becomes a real risk when outdoor temperatures at night do not drop below 18 to 20 degrees Celsius, depending on the species. In combination with high humidity, this threshold shifts even lower. In practice, the Temperature-Humidity Index (THI) is used as the standard measure.
For dairy cattle, a THI of 68 is considered the critical threshold above which production losses occur. In poultry, the thresholds are slightly higher, but here too a THI above 72 causes measurable damage. When the nighttime THI approaches or exceeds these values, recovery becomes impossible and cumulative stress begins to build.
In the Belgian and Dutch context, warm summer nights are increasingly becoming a reality. In 2026, there have already been several periods during which nighttime temperatures remained above 20 degrees Celsius for multiple consecutive days, structurally raising the risk of nighttime heat stress in our region as well. Farmers in Southern Europe, the Middle East, and Southeast Asia have been dealing with chronic nighttime heat stress as a standard condition for years.
How can betaine help reduce heat stress?
Betaine helps reduce heat stress by functioning as an osmolyte: it protects cells against dehydration and shrinkage when thermal load is high. This mechanism works both during the day and at night, supporting cellular stability even when recovery is absent due to persistent heat.
As an osmolyte, betaine attracts and retains water within the cell, making it more resistant to the osmotic stress caused by heat. This has direct benefits for the intestinal barrier, muscle cells, and immune system cells. Research shows that betaine increases the expression of tight junction proteins such as occludin and claudin-1, protecting intestinal integrity even under heat stress conditions.
In broilers under heat stress, betaine improves breast muscle weight through better cellular hydration and antioxidant protection. In sows, betaine is most effective during heat stress periods such as summer breeding, where it contributes to more piglets born alive and better weaning weights. In ruminants, betaine supports osmotic balance in the rumen and helps maintain more stable milk production during warm periods.
You can find more information about how this ingredient works on our page about natural betaine. Betaine is not a substitute for cooling or ventilation, but a physiological support that structurally strengthens the animal’s resilience — including during the critical nighttime hours.
Which management measures are most effective at reducing nighttime heat stress?
The most effective management measures against nighttime heat stress focus on ventilation, feeding time, and water availability. Cooling the environment has the greatest impact, but adjustments to feed and drinking water management can also significantly reduce the physiological burden.
- Optimize ventilation during nighttime hours: Ensure that ventilation systems run at maximum capacity throughout the night. Nighttime air is cooler than daytime air and can be actively used to lower barn temperature.
- Adjust feeding times: Move the largest feed delivery to early morning or late evening, when temperatures are at their lowest. Digestion generates body heat, which worsens heat stress if it coincides with the warmest hours.
- Guarantee continuous access to cool drinking water: Water intake increases significantly during heat stress. Ensure that water lines and nipples are clean and that water temperature is kept as low as possible. With drinking water additives, dosing is fully flexible and controllable, making them a practical tool.
- Temporarily reduce stocking density: Fewer animals per square meter means less body heat generated inside the barn, which accelerates nighttime cooling.
- Add electrolytes and supportive additives to drinking water: Heat stress disrupts electrolyte balance. Supplementation via drinking water helps restore osmotic balance and supports feed intake the following morning.
A combination of structural measures (ventilation, insulation, shade) and nutritional measures delivers the best results. Farmers who focus solely on cooling without adjusting their feed and drinking water management leave a significant portion of the potential gains on the table.
How Jodoco helps with heat stress at night and during the day
At Jodoco, we have spent the past 25 years specializing in the development of natural solutions that make animals more resilient against stress, including heat stress. Our approach combines scientifically supported ingredients in formulas that work both during the day and at night — when recovery is absent and physiological pressure is at its greatest.
Our products provide concrete support at the most critical moments:
- Jodobet is our natural betaine derived from sugar beets, which protects cells as an osmolyte, strengthens the intestinal barrier, and reduces thermal load at the cellular level. Effective in poultry, pigs, and ruminants.
- Jodoplume is a liquid combination of betaine, organic acids, and copper for administration via drinking water, specifically suited for heat or coccidiosis stress. Ideal for use when feed intake drops but water intake remains high.
- Our drinking water and feed additives are flexible in application and can be quickly adapted to the situation on your farm, even during an acute heat wave.
Want to know which approach best fits your farm situation? Contact our team. We are happy to work with you on a practical, scientifically grounded strategy against heat stress — day and night.
Related Articles
- How does betaine affect carcass quality in pigs?
- What is the difference between daytime heat stress and nighttime heat stress?
- How does heat stress affect feed intake in cows?
- How do you protect livestock from heat stress in the summer of 2026?
- How does heat stress affect the immune system of livestock?
