Heat Stress in Dairy Cows: Causes, Effects, and Prevention Strategies

The heat and humidity of summer can combine to make a very uncomfortable environment for dairy cows and be a concern for dairy producers.

When does heat stress occur in dairy cows?

Heat stress occurs when high temperatures combine with elevated humidity levels, making it difficult for dairy cows to regulate their body temperature. Because dairy cattle perform best in cooler conditions, prolonged exposure to heat can negatively impact animal health, milk production, and reproductive performance.

The optimal environmental temperature for dairy cows ranges from 23°F (-5°C) to 65°F (18°C). When temperatures rise above this range, producers should take steps to help cattle stay cool and comfortable.

Effects of heat stress can include:

• Reduction in dry matter (DM) intake
• Reduction in milk yield with lower fat and protein levels
• Reduced fertility
• Increased water consumption

How do cows cool themselves?
To cool down, cows will raise their respiration rate and start panting, which leads to increased salivation. That, in turn, reduces buffer capacity and increases the risk of ruminal acidosis. Additionally, cows suffering from heat stress spend two to three hours per day less lying down. This increases the chance of hoof disorders. Good hoof health is necessary for optimal cow flow to the milking robot.

How much water do dairy cows need during hot weather?

Water is one of the most important tools for managing heat stress. High-producing dairy cows may consume up to 50 gallons (200 liters) of water per day during hot weather. A useful guideline is that a cow typically requires four times as much water as her daily milk production.

Producers should ensure clean, fresh water is readily available at all times and that water access points are sufficient for the entire herd.

How to reduce heat stress for dairy cows? 

Below are a few considerations in reducing heat stress. These measures do not only apply to lactating cows, but to dried-off cows and heifers as well.

• Water: High-yielding cows may drink up to 50 gallons (200 liters) per day. The general rule of thumb is that the water required by a cow equals four times her daily milk yield.
  
• Housing: Cows need ventilation to cool off. Natural side-ways ventilation in open-sided barns, together with mechanical ventilation from 60ºF (20°C) onward, is the most effective. Remember to check the louvers as well. Dust can reduce air flow by 30 percent.
  
• Feed management: Feeding more often, at cool moments of the day, keeps the ration fresh as well as stimulating feed intake and preventing fermentation. The Lely Vector automatic feeding system helps maintain feed quality throughout the day by delivering fresh feed multiple times daily. The Lely Juno feed pusher  keeps feed within easy reach by pushing it up to the feed fence multiple times throughout the day.
  
• Pasture: During hot periods, it is advisable to have the cows in pasture only during the night or during the cool parts (evening, early morning) of the day.
  
• Monitoring: Early detection of heat-stress-related changes allows producers to respond quickly before performance declines become more severe. The Lely Horizon farm management platform provides valuable insights into herd performance and behavior.

Heat stress can significantly impact dairy cow health, productivity, fertility, and overall herd performance. Providing adequate water, optimizing barn ventilation, adjusting feeding schedules, and managing pasture access are effective strategies for reducing heat stress and supporting cow comfort throughout the summer months.