Nobody likes excessive heat. But unlike humans, cows get uncomfortably hot at temperatures that most people tolerate easily. Their sensitivity to heat can lead to heat stress, which reduces milk production and affects their health. Read on to discover how to recognize and alleviate heat stress in dairy cattle.
What Causes Heat Stress in Cattle?
Heat stress in cattle occurs once their bodies absorb and generate more heat than they can get rid of. Cows produce heat by consuming feed, producing milk, and growing. They also absorb solar heat and heat from the ambient air.
Cattle cool down by radiating, convecting, and conducting heat when they are hotter than their surroundings. But they rely on breathing and air movement (wind/fans) to cool down when it’s warmer outside than their body temperature. Does a cow sweat? Yes, but not effectively, so they rely less on this cooling-down method.
The normal temperature of a cow is about 101.5-102.5°F. But, cows experience mild heat stress starting at just 72°F with 50% humidity.
Humidity plays a critical role in determining if the current conditions pose a risk of heat stress for your cattle. The temperature-humidity index (THI) represents the combined effect of air temperature and humidity and their level of thermal stress. If the humidity is high, cows can’t quickly lose heat through sweating and respiration because the air is already saturated with moisture.
| Temperature-humidity index (THI) | Heat stress level | Cow body temperature (°F) |
|---|---|---|
| Below 68 | No heat stress | 101.5-102.5 |
| 68-71 | Mild | 102.5-103 |
| 72-79 | Mild to moderate | 103-104 |
| 80-90 | Moderate to severe | 104-105 |
| 90-99 | Severe | Above 105 |
Use the table below to calculate the THI based on your weather forecast data. This will help you determine the risk of heat stress for your cattle and take appropriate preventive measures.
| Temperature-humidity index (THI) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Relative Humidity (%) | |||||||||
| Temperature (°F/°C) | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
| 72/22 | 66 | 66 | 67 | 68 | 69 | 69 | 70 | 71 | 72 |
| 75/24 | 68 | 69 | 70 | 70 | 71 | 72 | 73 | 74 | 75 |
| 79/26 | 70 | 74 | 72 | 73 | 74 | 75 | 77 | 78 | 79 |
| 82/28 | 72 | 73 | 74 | 76 | 77 | 78 | 80 | 81 | 82 |
| 86/30 | 74 | 75 | 77 | 78 | 80 | 81 | 83 | 84 | 86 |
| 90/32 | 76 | 77 | 79 | 81 | 83 | 84 | 86 | 88 | 90 |
| 93/34 | 78 | 80 | 823 | 84 | 85 | 87 | 89 | 91 | 9 |
| 97/36 | 80 | 82 | 84 | 86 | 88 | 90 | 93 | 95 | 97 |
| 100/38 | 82 | 84 | 86 | 89 | 91 | 93 | 96 | 98 | 100 |
| 104/40 | 84 | 86 | 89 | 91 | 94 | 96 | 99 | 101 | 104 |
Effects of Heat Stress on Dairy Cattle
Heat stress not only harms your dairy cattle, but the impact on their health can reduce your profits, with the potential for long-term consequences. Heat stress can have the following effects on dairy cattle:
- Reduced feed consumption and milk production for lactating cows
- Decreased protein and fat content in produced milk
- Lowered pregnancy rates and fertility decline in male and female cattle
- Increased oxidative stress and lowered the immune system
- Increased risk of diseases and severe health issues
- Reduced saliva availability for the rumen and lowered rumen pH
- Loss of vital minerals through elevated sweating (K, Na, Mg)
- Shortened gestation period in late gestation cows and lowered birth weight.
- Reduced milk production of heifer calves from heat-stressed cows for the first 30 weeks
| Estimated Daily Milk Production Loss Per Cow | |
|---|---|
| Heat Stress Level | Milk Loss (lbs/day) |
| Mild | 2.5 |
| Mild to moderate | 6 |
| Moderate to severe | 9 |
| Severe | 10+ |
Signs of Heat Stress on Cattle
Observe your dairy cows for these signs of heat stress during hot weather:
- Labored and increased respiration rates (above 75/minute indicates mild to moderate heat stress), according to the University of Minnesota
- Slobbering
- Gathering in groups. This is counter-intuitive, but cattle tend to bunch together when heat stressed, which exacerbates heat accumulation
- Increased body temperature
- Frustrated, aggressive, or lethargic behavior
- Breathing with mouth open and panting with extended necks
- Spending more time standing
- Decreased milk production
- Reduced dry matter intake
How to Prevent Heat Stress in Dairy Cattle
Water, shade, ventilation, and nutrition are not just elements of cattle care. They are your tools to prevent heat stress and keep your dairy cows cool and content. Understanding their importance is key to managing heat stress in your herd.
Water
Provide lots of clean water between 40–65°F in their water troughs. As noted by Michigan State University, cows will drink less when the water temperature exceeds 80°F. Water intake rises dramatically for heat-stressed cows, so ensure sufficient water supply in their housing.
A sprinkler system can keep cows cool. But it will increase humidity if the barn isn’t well-ventilated. Excessive sprinkling may also cause mastitis if the water runs down to the udder.
Shade and Cover
Shade reduces the effect of solar radiation and helps keep cows cool. However, you must provide adequate shade areas to prevent crowding and restricted airflow. Kansas State University recommends about 30–40 square feet per mature cow and 15–20 square feet for yearling calves.
Avoid Handling Cattle
Avoid handling, processing, and moving cattle during high temperatures unless necessary. If you must handle your daily cows, it’s best to do it in the early morning hours when temperatures are lower.
Ventilation
Natural or mechanical ventilation can help cows lose heat from the air flowing past them. You can use fans to increase the air velocity and keep the cows comfortable. Fans can significantly reduce heat stress and help keep the stall dry and cows healthier.
How Nutrition Affects Heat Stress in Dairy Cattle
Feeding time and feed quality can worsen or help alleviate heat stress in dairy cattle. Dry matter intake (DMI) and milk production drop under heat stress, but proper nutrition management can help improve both.
Feeding Time
Shifting feed intake to cooler parts of the day can help prevent excessive heat buildup from the digestive system. Peak digestive heat production occurs about three hours after consuming feed, so it’s best if the peak heat occurs during the morning and evening.
Feed Quality
Providing high-quality dairy cattle feed increases the diet energy content and decreases the heat associated with the fermentation of lower-quality forages. For example, fermentation heat may be reduced by including corn in the diet because it ferments slower than wheat grain. Likewise, adding fat to the cattle feed ingredients might decrease heat during digestion while increasing the available energy.
Heat stress increases the maintenance energy requirements by 7–25%, an equivalent of 2.2–7.5 lbs of milk production. So, increasing the nutritional density with high-quality feed is critical to boost cow milk production during hot seasons.
The experienced staff at Star Blends can work with your dairy nutritionist to formulate a custom, high-quality feed at an economical price. Focusing on the optimal animal nutrition for your dairy cattle can help optimize production and enhance milk quality.
Micronutrients
Heat-stressed cows have a five-fold increase in potassium loss due to sweating, according to Dairy Herd Farm Journal. Heat stress also depletes vitamin C levels in tissue and plasma. So, mineral and vitamin supplements may be necessary for optimal health and dairy production.
Custom-Made Nutrition For Your Dairy Cows
Feed and nutrition can significantly impact how dairy cattle handle heat stress, and proper nutrition can help mitigate some of the adverse effects. Star Blends is here to help keep your herd happy and healthy — no matter the time of year.
Our cattle feed experts will work closely with your nutritionist to create a custom feed that will support your cows throughout the hot months. Get in touch today to learn more.
