Grazing helps reduce heat stress in cows because they can search for shade, cooler spots, and a light breeze that lowers body temperature. That said, grazing is not a universal solution: in extreme heat, pasture can actually be detrimental if no shade or sufficient drinking water is available. In this article, we answer the most frequently asked questions about heat stress and grazing in dairy cattle.
What are the effects of heat stress on dairy cows?
Heat stress in dairy cows occurs when the combination of temperature and humidity exceeds the animal’s ability to dissipate heat. This leads to reduced feed intake, lower milk production, poorer reproductive performance, and in severe cases, serious health problems. The consequences are significant both economically and for animal welfare.
Cows are heat-producing animals. The digestion of roughage releases a large amount of metabolic heat, meaning they can experience heat stress at relatively moderate temperatures of around 22 to 25 degrees Celsius, especially at high humidity. High-producing dairy cows are particularly vulnerable because they generate more heat.
The effects of heat stress in dairy cattle are wide-ranging and interconnected:
- Reduced feed intake: Cows eat less to limit the production of metabolic heat.
- Lower milk production: Reduced feed intake directly translates to less milk and a lower protein content.
- Poorer reproduction: Estrus becomes less visible, conception rates decline, and early embryonic loss occurs.
- Disrupted rumen function: Changes in eating patterns increase the risk of rumen acidosis.
- Weakened immune system: Chronic heat stress suppresses the immune system, making cows more susceptible to infections.
- Increased water intake: Cows drink considerably more, placing extra pressure on the water supply.
At the cellular level, heat stress acts as an osmotic stressor: cells lose moisture and become imbalanced. This is precisely the mechanism where osmotic support — such as through natural betaine — can play a role in protecting cells and supporting gut health under stress conditions.
How does grazing help cool cows down?
Grazing gives cows the opportunity to actively seek out cooling. In the pasture, animals can benefit from a light breeze, shade from trees or hedges, and cooler ground in the early morning. This behavioral adaptability is a natural and effective mechanism for regulating body temperature.
In a well-managed pasture, cows have more space than in a barn, which means heat production per unit of area is lower. They can spread out, are not crowded together, and are exposed to airflow that promotes evaporative cooling through the skin and respiration.
Grazing also has an indirect effect on welfare. Cows that can graze outdoors show less stress behavior and have lower cortisol levels. Less stress means a better-functioning immune system and a more stable metabolism, which partially offsets the negative effects of heat.
It is important to emphasize, however, that grazing only provides cooling when conditions are right. Without shade, sufficient drinking water, and access to cooler pastures, the field can actually become a heat trap — especially in the afternoon when solar radiation is at its peak.
When is grazing beneficial in the heat, and when is it not?
Grazing is beneficial in hot weather when cows have access to shade, sufficient drinking water, and cool pastures, and when they are outside in the early morning or evening. During extreme daytime heat and without shade, housing cows with active ventilation is better for the animal.
The decision to keep cows outside or house them when temperatures are too high depends on several factors. A practical guideline is the Temperature Humidity Index (THI): above a THI of 68, most dairy cows begin to experience heat stress. Above a THI of 72, active intervention is necessary.
Grazing is beneficial when:
- Cows are turned out early in the morning or after sunset, when temperatures are lower.
- The pasture offers sufficient natural shade through trees, hedges, or artificial screens.
- There are multiple water points with fresh, cool water available in the field.
- Humidity is low and a light breeze promotes evaporative cooling.
- Cows have the option to choose between being outside and a cool, ventilated barn.
Grazing is not recommended when daytime temperatures rise above 28 degrees Celsius in combination with high humidity, when no shade is available, or when the water supply in the pasture is inadequate. In that case, a well-ventilated barn with fans and possibly misting systems offers more comfort than the open field.
What other measures enhance the effect of grazing?
Grazing works best as part of a broader set of heat stress management measures. Adjustments to feed management, water supply, and the barn environment significantly enhance the effect of grazing and help keep dairy cattle production and health stable.
The following measures complement grazing as a strategy:
- Adjusting the feeding schedule: Provide the largest portion of the ration during the cooler evening and nighttime hours. This reduces metabolic heat production during the day.
- Optimizing the water supply: Ensure sufficient water points both in the pasture and in the barn. In hot weather, cows can drink up to 150 liters per day. Water temperature and availability are critical.
- Barn ventilation: Combine grazing with good air circulation in the freestall barn during the periods when cows are housed.
- Shade structures in the pasture: Plant trees along field boundaries or install mobile screens at strategic locations.
- Ration adjustments: Reduce roughage with high fermentation heat and consider energy-dense, easily digestible components to maintain feed intake.
- Support through drinking water additives: Drinking water additives can support osmotic balance and improve cellular hydration during heat stress.
The combination of grazing during cooler hours and barn management during the day gives cows the best of both worlds: the behavioral freedom of the pasture and the protection of a controlled environment.
How do you recognize heat stress in cows at pasture?
Heat stress in cows at pasture can be recognized by an elevated respiratory rate, heavy panting, clustering in the shade, reduced grazing, and a noticeably higher water intake. When cows are breathing more than 60 times per minute, heat stress is clearly present and action must be taken.
In the pasture, the signs are sometimes less obvious than in the barn, but if you know what to look for, they are easy to identify. Cows that normally graze actively will stand still in the shade during heat, with their heads lowered and their flanks moving rapidly. They visit water sources more frequently and drink in short, intensive bouts.
An overview of the most recognizable signs:
- Respiratory rate above 60 per minute: This is the earliest and most reliable sign of heat stress.
- Clustering in the shade: Cows gather together in the coolest spot in the pasture.
- Reduced grazing behavior: Cows stand still instead of grazing actively, even in the morning.
- Excessive salivation and panting: Visible saliva and an open mouth are signs of severe heat stress.
- Lower milk production at the next milking: A sudden drop in production without another identifiable cause points to heat stress.
- Restless behavior during milking: Cows experiencing heat stress are more often tense or agitated.
Early intervention is essential. When you observe several of these signs simultaneously, it is time to move the cows to a cooler environment, check the water supply, and adjust the feeding schedule. The faster you respond, the less impact there will be on production and health.
How Jodoco helps with heat stress in dairy cattle
Heat stress is a complex challenge that requires more than a single measure. Grazing is a valuable tool, but the underlying cellular and metabolic effects of heat call for targeted nutritional support. At Jodoco, we develop products that intervene at precisely that level.
Our approach is based on the action of natural betaine as an osmolyte: it protects cells against dehydration and osmotic stress, supports the intestinal barrier, and helps maintain metabolic balance in warm conditions. In ruminants, betaine also contributes to microbial protein synthesis in the rumen and the production of short-chain fatty acids, which helps sustain feed intake and milk production.
Specifically, we offer the following solutions for dairy cattle:
- Acibet G: A liquid source of betaine, glycerol, and organic acids that supports liver function, reduces negative energy balance, and stimulates feed intake — including during heat stress.
- Jodobet: Natural betaine as an osmolyte and methyl donor, proven effective in reducing heat stress and improving technical performance.
- Drinking water administration: Our products are easy to administer via drinking water, which is especially advantageous during heat stress since water intake remains more reliable than feed intake.
Want to find out which approach best suits your operation or your customers’ needs? Contact us and we will be happy to work with you on a concrete, science-based strategy for managing heat stress in dairy cattle.
