Quick Summary for Producers:
Threshold: Start cooling when the THI (Temperature-Humidity Index) hits 68.
Water: Ensure a flow rate of 1.5 gal/hour per head.
Movement: Handle cattle only before 10:00 AM.
Fly Control: Essential to prevent "bunching" which traps heat.
As temperatures rise, look for signs of heat stress in your cattle. It’s important to spot heat stress symptoms early to provide effective relief to livestock during the hot and humid summer months.
Heat stress costs the U.S. livestock industry an estimated $2.4 billion annually in lost production — making early detection and proactive management one of the highest-return investments a producer can make.
“Recognizing the effects of heat stress during the hot and humid summer months is important for keeping your cattle healthy and productive,” says Dr. Erika Nagorske, a practicing veterinarian with Southwest Veterinary Services.
Download the free guide How to Manage Heat Stress in Cattle or continue reading below, where we will cover:
The Temperature-Humidity Index (THI) is a combined measure of ambient temperature and relative humidity used to estimate heat load on livestock. Unlike temperature alone, THI accounts for the fact that high humidity prevents evaporative cooling — meaning cattle can't sweat or pant their way to relief.
A THI of 68 is the established threshold at which cattle begin to experience measurable heat stress, and management interventions should begin before that number is reached.
Because high humidity prevents evaporative cooling (sweating/panting), ambient temperature alone is a deceptive metric. Monitoring the index is critical for proactive management.
Heat stress happens when cows absorb and create more heat than what they can easily eliminate, explains the University of Minnesota Extension. Cattle don’t sweat effectively. They instead rely on their own respiration to cool themselves.
Be on the lookout for these key symptoms, adapted from Kansas State University and USDA livestock heat stress guidelines:
Stage 1 (Early): Elevated breathing rates and increased salivation.
Stage 2 (Moderate): Open-mouth breathing and "bunching" behavior in shade.
Stage 3 (Severe): Lack of coordination, tongue protrusion, and inability to stand.
Some of the most common effects of heat stress include:
Change in behavior
Increased susceptibility to disease
Reduced weight gain
Lower milk production
Reduced breeding efficiency
Death
Remember that heat stress is not limited to older animals; it can also affect even young calves. But generally, animals with past health issues will be the first to be affected by heat stress — they will also be the most severely affected.
Outdoor pests like flies can worsen heat stress by aggravating the animals and causing them to crowd together, hoping the flies will affect their neighbors instead of themselves.
You’ll often see cattle gathered together in a pen, stomping and kicking manure trying to fight flies away. As cattle attempt to deal with the fly problem, they will avoid lying down or drinking water. Unfortunately, these behaviors further exacerbate heat stress.
Having an effective fly control program in your arsenal will help curb some of the stress that the heat brings to your animals. Incorporating feed additives is a smart and effective way to curb fly infestations.
Insect growth regulator (IGR) products are fly control feed additives that can disrupt fly larvae from developing in the manure of the treated animal. There is no risk to the animal because the IGR isn’t actually absorbed but instead passes through the animal’s manure. By stopping the pests from developing into biting adult flies, you’ll prevent a potentially expensive impact on your herd.
Luckily, IGR is a very cost-effective fly control approach. Both Sweetlix® with ClariFly® and Sweetlix® Classic Cow-Calf with Clarifly® nutritional supplements contain Diflubenzuron Insect Growth Regulator for continuous feeding to cattle through the fly season. Similarly, ClariFly® Larvicide Premix 0.67% is intended for blending into feeds or supplements as part of an integrated pest management program aimed at reducing fly populations in the treated environment.
Start including fly control additives in your feeding program early in the spring, usually about 30 days before the average daily temperature reaches 65 ℉ or when flies begin to appear. From this point, it’s key to continue using fly control in your feed until 30 days after the first frost in the fall. Continuing treatment in the fall is just as important as starting early in the spring.
Proactive treatment later in the year will help control the next year’s fly population by preventing horn fly larvae from hibernating and surviving the winter (also known as overwintering) below manure pattie before later developing into adult flies.
Learn more about why your fly control strategy should include feed additives here.
When managing and treating heat stress, it’s critical for cattle to have consistent access to the following three things:
As both temperatures and physical activities rise for animals, so does their need for increased water intake. A 1,000lb animal requires 1.5 gallons of water per hour during peak heat. Ensure your trough flow rate can meet this demand without cattle crowding.
During the summer months, automatic water tanks may not be able to keep up with your animals’ hydration demand. Adding a stock tank of clean and cool drinking water to a pen for your animals can provide extra hydration and help stabilize their internal temperature.
For cattle already showing signs of dehydration, Bovine BlueLite is an oral electrolyte supplement designed to rapidly restore fluid balance and energy in heat-stressed animals. It can be added directly to drinking water and is especially effective during peak heat periods.
Help cattle reduce their body temperature by providing proper shade during extremely warm days. Shade from trees and buildings is effective when animals have between 20 to 40 square feet of shade.
Spreading your cattle out to provide them with adequate space during high temperature days will likely prevent them from crowding one another and help with heat abatement.
Also ensure that barns or anywhere else cattle gather have adequate ventilation. This can be as simple as adding fans to provide consistent airflow when necessary. If you do add fans to your ventilation system, it’s important to conduct proper maintenance on your equipment to ensure air flow is not reduced or blocked.
Peak heat season is here. Having the right products on hand before temperatures climb means you're treating animals in the barn — not scrambling to place an order during a heat event.
FBN offers a broad portfolio of Animal Health products that can help minimize dehydration, including:
Lactated Ringer's Solution – An IV fluid replacement used to treat severe dehydration and electrolyte loss in cattle that can no longer maintain hydration through drinking alone.
Complete Dehydration Treatment (CDT) – An oral rehydration formula for moderately dehydrated cattle. Easy to administer and effective for Stage 1–2 heat stress cases.
Bovine BlueLite – An electrolyte and energy supplement added to drinking water. Best used proactively during hot stretches and for early-stage dehydration.
Looking for everything in one place? Shop FBN's full livestock health catalog for fly control, electrolytes, rehydration treatments, and more — all priced transparently and shipped directly to your farm.
If a product requires a prescription, our team can contact your preferred veterinarian on your behalf if you provide their contact information during checkout. Get step-by-step instructions on how to shop FBN’s Animal Health store here.
Find key cattle products and other livestock essentials to keep your herd healthy at FBN.
At what temperature does heat stress start in cattle?
Heat stress begins when the Temperature-Humidity Index (THI) reaches 68 — not a specific air temperature alone. A day that's 85°F with high humidity can be more dangerous than a dry 95°F day. Monitor THI rather than temperature in isolation.
How long does it take cattle to recover from heat stress?
Mild cases (Stage 1) typically resolve within a few hours once animals have access to shade, water, and ventilation. Moderate to severe cases can take 24–48 hours and may require oral or IV rehydration support.
Are calves more susceptible to heat stress than adult cattle?
All ages are vulnerable, but cattle with prior health issues are typically affected first and most severely. Young calves have limited ability to regulate body temperature and should be monitored closely during heat events.
Can heat stress kill cattle?
Yes. Stage 3 heat stress — characterized by loss of coordination, tongue protrusion, and inability to stand — can be fatal without immediate intervention. Death losses are most common in animals that are already compromised by illness or poor body condition.
How much water do cattle need during a heat event?
A 1,000 lb animal requires approximately 1.5 gallons of water per hour during peak heat. Ensure your trough flow rate can meet this demand; automatic waterers may not keep up during prolonged heat events.
When should you stop handling or working cattle in summer?
Cattle should only be handled before 10:00 AM during hot periods. Working cattle later in the day adds exertion stress on top of ambient heat stress and can push animals into dangerous territory quickly.
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