Home / Guides / Herd Health & Disease Management
Herd Health & Disease ManagementHeat Stress in Dairy Cows: Health Impacts
Dairy cows make a great deal of heat just digesting feed and making milk, so hot weather hits them hard. Spotting stress early and cooling cows well protects health, fertility and production.
Key points
- Heat reduces intake, milk and fertility and can raise disease risk.
- Watch cows at the hottest time of day for breathing, standing and crowding.
- Shade, fans, sprinklers and water form the core of cooling.
- Include dry and close-up cows.
- Plan and repair equipment before summer.
What heat stress does to a cow
Cows cannot shed heat easily. When the air is hot and humid, they breathe faster, drool, eat less and seek shade or water. The more milk a cow makes, the more heat she produces.
Prolonged heat can reduce milk, lower fertility, weaken the immune system and increase the risk of other diseases. Dry cows and late-pregnant cows are affected too, and heat before calving can influence the calf and the cow's next lactation.
Early signs to watch
Watch your cows at the hottest times of the day, not just at milking. A cow in distress breathes quickly with an open mouth, stands more than she lies, bunches in shade and stops eating. Manure can become looser and milk may fall.
Heat is a combination of temperature, humidity, sun and air movement. Your extension office can help you read a heat index and decide when to turn on added cooling.
- Rapid breathing and open-mouth panting
- More standing, less lying
- Crowding at waterers and shade
- Falling feed intake and milk
Cooling cows: shade, air and water
The three basics are shade, air movement and water. Provide shade where cows rest and wait. Use fans where air does not move, and consider sprinklers combined with fans, which cool cows through evaporation. Your extension specialist can help you design a system sized to your barn or lot.
Make sure cows always have plenty of clean, fresh water. Heat increases water intake, and a trough that cannot refill quickly will leave cows short.
- Shade where cows rest, eat and wait
- Fans over stalls and feed lines
- Sprinklers with air movement, as your extension advisor recommends
- Clean waterers with enough flow and space
Feeding and management changes
Cows eat less in heat, so the ration needs to deliver enough nutrients in less feed. Your nutritionist can adjust the ration, minerals and feeding times. Feed more in the cooler parts of the day and keep the bunk fresh.
Reduce time cows spend in hot holding areas. Move groups gently, avoid crowding and handle cows when it is coolest, since stress adds to heat load.
- Ask your nutritionist about hot-weather rations
- Shift feeding toward cooler hours
- Shorten time in the holding pen
- Clean and push up feed more often
Health and fertility effects
Heat can make cows less likely to show heat and less likely to hold a pregnancy. It can also contribute to lameness, since cows stand more, and to a rise in mastitis as cows and bedding stay wet and warm.
Dry cows and close-up cows need cooling as much as milkers. Your vet may suggest changes to breeding programs in the hottest months.
- Review breeding programs with your vet in summer
- Watch for lameness and udder health
- Cool dry and close-up cows
- Record weather and herd performance together
Planning before the hot season
Do not wait for the first heat wave. Inspect fans, sprinklers, waterers and shade in spring. Repair, clean and test equipment. Train staff to recognize heat stress and to know what to do on a hot day.
Write a short heat plan: who checks cows, when to turn on cooling, which cows get priority, and who to call. Electrical equipment in wet barns can be dangerous, so follow manufacturer and electrical safety guidance, and use qualified electricians.
- Service fans and sprinklers before hot weather
- Check electrical safety
- Post a plan and phone numbers
- Train new staff
Common mistakes
Running cooling only when cows are already in trouble, forgetting dry cows, letting waterers run low and not tracking performance against the weather are the usual errors. Also, mistaking a cow that is simply hot for one that is sick can delay a vet call. Always follow label or vet-set withdrawal times if any treatment is given.
Sources and further reading
- University of Florida IFAS Extension
- Texas A&M AgriLife Extension
- University of Wisconsin-Madison Extension
- Penn State Extension
Organization homepages are linked so you can search them for current guidance on this topic.