Submitted by: Daniela Roland, Penn State Extension Franklin County Dairy Educator
Dairy cows perform best in cool conditions, and as temperatures rise, heat stress can quickly affect milk production, reproduction, and overall herd health. Now is a good time for farmers to ensure cooling strategies are in place to keep their cows comfortable and productive.
A dairy cow’s thermoneutral zone is in the range of 40 to 70 ˚ F. As temperatures increase, dairy cattle can become heat stressed and this can negatively affect milk production and somatic cell counts. Higher temperatures and environmental stress can cause elevated somatic cell counts (SCC).
All ages of dairy animals can be impacted by heat stress. For higher-producing lactating cows, it’s been shown that they can experience heat stress when the Temperature Humidity Index is 68 ˚ F or greater. And as humidity increases, an average-producing dairy cow could become heat-stressed at 72˚F. Dry cows can also be negatively affected by heat stress. In a 2016 study on the economics of cooling dry cows, it was estimated that dry cows housed under no heat abatement in Pennsylvania lose over 1,000 pounds of milk in their subsequent lactation.
Fortunately, several management practices can help reduce the effects of heat stress and maintain animal performance during hot weather.
-Fans, sprinklers, and other ventilation systems are effective tools for reducing heat stress. Be sure to clean barn fans. Dirty, dusty fans won’t run as efficiently as clean fans. Dust buildup of 1/8-inch on blades can decrease fan efficiency by as much as 40%. Keeping fans clean is important to ensure the effectiveness of the ventilation system so cows stay cool and comfortable.
-Provide plenty of fresh, clean water. Cows drink about 50% more water when the temperature is 80˚F versus 40˚F. They need water to cool themselves through increased respiration and perspiration. Watering stations should be in convenient locations to allow for multiple cows to access the water and keep up with water demand. If cows are housed in tie-stalls, be sure to clean out water bowls frequently to keep them free of feed and debris.
-When possible, schedule vaccinations and other handling activities during cooler parts of the day to minimize additional stress on animals.
-Feed during the cooler parts of the day, such as early morning or evening. Cows consume less feed during hot weather, and reduced dry matter intake can quickly translate into lower milk production. Some estimates show that for every one pound decrease in dry matter intake, 2 pounds of milk production are lost.
-Provide shade as much as possible and if cows are milked in a parlor, limit time in the holding pen.
In addition to implementing cooling strategies, monitoring herd records can help identify whether heat stress is affecting performance.
Signs of heat stress will show up in the following ways:
-Reduced milk production. Use daily milk weights to look for drops in milk production of more than five pounds per cow per day during warmer weather. It’s not recommended to use monthly tests as the impact of heat stress can come and go between tests.
-Decrease in conception rates. Look for a decline in conception rate of five points or more during the summer months compared to the annual average conception rate.
-Increase in cases of lameness. Monitor hoof health records for an increase in lameness rates two months after the main heat stress period, which is usually observed in early fall. When cows are heat-stressed, they tend to bunch together or stand up, which can affect hoof health.
While heat stress can challenge even well-managed dairy herds, proactive management can significantly reduce its impact. Maintaining adequate ventilation, water availability, shade, and feeding management can help cows remain comfortable, productive, and healthy throughout the summer months.
If you have questions or would like more information, contact Daniela Roland, the Franklin County Dairy Educator at 717-263-9226 or djr6158@psu.edu.
