As summer temperatures rise, it’s important to understand the impact of heat stress on your cattle — and what you can do to minimize it. We talked to Dr. Grant Dewell, a beef cattle veterinarian with over 30 years of experience, about what you need to know about heat stress in both dairy and beef cattle.

Understanding heat stress

In simple terms, heat stress occurs when cattle can’t dissipate heat as fast as they accumulate it. Dr. Dewell explained that cattle are more susceptible when temperatures rise than some other animals for three reasons:

1. Because of their large body mass, cattle accumulate more heat compared to smaller livestock.
2. Their normal physiological processes, like rumen fermentation, generate heat.
3. They have poor lung capacity, which makes panting less effective at cooling them off.
4. Dr. Dewell pointed out that different breeds of cattle have different thermoneutral zones — but all cattle have lower heat tolerance than humans, especially for cattle still carrying heavy winter coats. “In late spring, when it’s getting above 75 degrees, it’s nice and comfortable short-sleeve weather for you… but cattle are thinking it’s getting hot outside. So, basically anytime it’s above 75 degrees, the cattle are spending energy trying to cool themselves off,” he said.

Humidity also plays a role in heat stress. “We also have to take into account what the humidity is … Evaporation is how we dissipate heat, and so if it’s a humid day, evaporation doesn’t work so well,” he added.

Recognizing the signs of heat stress in cattle

Early detection is key to mitigating the effects of heat stress. Dr. Dewell outlined the progression of signs you should watch for in your herd.

• Increased respiratory rate and panting: This is often the first visible sign of heat stress as cattle switch to respiration when sweating is no longer sufficient.
• Restlessness and increased standing: Heat-stressed cattle tend to stand more often, seeking any possible relief.
• Drooling and frothy mouth: As heat stress intensifies, cattle may begin to drool excessively.
• Open-mouth breathing with tongue hanging out: This indicates severe heat stress.
• Excessive drooling followed by cessation of drooling: The latter is a critical stage signifying severe dehydration where the animal lacks enough body water for evaporative cooling.

Long-term impacts of heat stress

Beyond the immediate discomfort, heat stress in cattle can have significant long-term physiological and economic consequences. Dr. Dewell highlighted a few of the major issues:

• Reduced feed intake and rumination: As cattle spend more energy trying to cool down, it leads to decreased feed consumption. “With moderate heat stress around 95º F, one would expect dry matter intake of feedlot cattle to drop by about 10%. With severe heat stress around 105 º F, we can see an almost 50% reduction in feed intake,” said Dr. Dewell. This impacts weight gain in feedlot cattle and milk production in dairy cows. ”With dairy cattle, we see about a 15-20% drop in milk production,” he added. Recurrent heat stress can lead to decreased gains over the entire feeding period.
• Reproductive issues: Heat stress can damage developing oocytes, impair estrous display in cows, reduce breeding activity as bulls also become less active, and decrease sperm quality. Embryo loss can also occur during early pregnancy. Dr. Dewell noted, “For beef cows, we can see up to a 20% reduction in pregnancy when there are moderate heat events during the breeding season. With severe heat stress, it can be over 30%.”
• Leaky gut syndrome: Increased body temperature and changes in feed intake can compromise the intestinal lining. This allows bacteria and toxins to cross into the bloodstream, potentially leading to immune problems and other metabolic disorders, including a possible link to liver abscesses in feedlot animals.

The critical link between water intake and heat stress

Water plays a vital role in helping cattle regulate their body temperature. Dr. Dewell stressed that water requirements increase in the summer compared to winter. During heat events, this need escalates even further.

“We’d expect water consumption to go up typically about twice as much in the summer compared to the wintertime. And then when we have a heat event, it’s going to go up even more. So if it’s just going from 20 to 30 degrees in January to 70 to 80 degrees in June, you’re about doubling your water intake. But when it gets up to 100 degrees, we’re increasing it up almost three times as much at that point just to try to get enough water intake,” he said.

“If you think about a 1,000-pound steer that needs 25 gallons at a minimum, that’s about a gallon an hour. That’s going to increase during a heat stress event. Then it’s going to go up 50% or so,” Dr. Dewell added. He also explained that lactating cows and those in active reproductive stages have already higher water demands. When heat stress is a factor, it drives that water demand up even higher.

The importance of your water system

The design and functionality of your water system are crucial. Dr. Dewell noted that while ponds can provide some cooling, they can compromise water quality. He prefers well-designed water systems that are easy to keep clean, especially in confinement settings where fecal contamination is more likely. Adequate drinking space is also essential.

To ensure adequate water intake, Dr. Dewell recommended that producers should aim for a water delivery flow of about 1.5 gallons per hour per animal. He advised checking water flow, especially in late spring, to ensure your systems can meet the increased demand.

Tips for ensuring continuous access to clean water

Dr. Dewell emphasized the need for continuous access to clean, fresh water during heat stress events. Here are three tips to make sure the water is flowing:

1. Check for adequate flow rate and supply: Water systems must be able to replenish quickly enough to meet the increased demand.
2. Ensure sufficient drinking space: Recommendations suggest two to three linear inches per head in feedlots to prevent dominant animals from restricting access.
3. Perform regular checks and maintenance: Water sources, whether automatic waterers or stagnant troughs, should be checked daily during the summer to ensure they are functioning correctly, are full, and are clean. Issues like clogged pipes or malfunctioning floats can quickly lead to water deprivation. You should also inspect for sludge buildup in pipes and ensure pressure regulators are working correctly.

Other practical solutions for managing heat stress in cattle

Dr. Dewell also offered several nutritional and management best practices that can help you mitigate heat stress in your herd.

• Shift feeding times: Feeding cattle in the late afternoon (at least 75% of the ration) can help reduce the peak of rumen fermentation heat during the hottest part of the day, as rumen temperature typically peaks about six hours after feeding.
• Adjust rations: In severe heat stress scenarios, slightly decreasing the corn content and increasing roughage (by 5-10%) can aid rumen buffering during fluctuating feed intakes.
• Provide shade: Shade is a critical but often underutilized tool, even in northern states.
• Consider sprinklers and bedding: Sprinklers can offer relief during extreme heat (though requiring significant water), and providing cornstalk bedding can insulate cattle from hot ground surfaces.

Key takeaways from Dr. Dewell

When you’re facing hot summer days, Dr. Dewell’s key advice is to plan ahead and prioritize water and shade. He said it’s critical to ensure all water systems are functioning correctly with adequate flow and access — and to develop a backup plan for water to prevent water deprivation during critical times

By understanding the science behind heat stress, recognizing the early warning signs and implementing proactive management strategies focused on water and shade, you can significantly mitigate the negative impacts of summer heat on your cattle.