It’s not the heat; it’s the humidity. That is a true statement for livestock dealing with hot summer days.

Humidity plays a large role in whether an animal feels heat stress. Therefore, farmers need to use the temperature humidity index, or THI, to gauge whether the animal is in moderate, severe or extreme stress because of heat.

THI is like a safety gauge to monitor heat stress. It is calculated using air temperature and relative humidity.

In cattle, heat stress can occur when THI is above 80 degrees F, or if nighttime temperatures consistently remain above 70 degrees, according to University of Missouri research.

Specifically for sheep and goats, South Dakota State University research shows heat stress occurs when THI is 82 to 84 degrees F (moderate), 84 to 86 degrees F (severe), and at more than 86 degrees F levels (extreme).

While cattle, sheep and goats can regulate body temperature to some extent by sweating, pigs lack this ability. Much of the hog industry relies on housing with controlled temperatures and humidity. But for those raising pigs outdoors or for youth projects, heat stress is a concern.

Michigan State University research finds that pigs that weight less than 60 pounds can adapt to heat and humidity better than those 175 pounds or larger. A temperature of 83 degrees with humidity at 70% can create a dangerous situation for pigs.

Anyone raising livestock should monitor THI and know these signs of heat stress.

What to observe

Livestock owners should monitor animal behavior and look for these clues:

But don’t wait for the signs of heat stress to appear, take precautions.

Reduce impact of heat, humidity

No matter the species, there are four common elements that every animal needs to help alleviate heat stress:

Water quality. Provide unlimited access to fresh and cool drinking water. Clean the tank often to keep algae and other parasites out. Keep in mind head space when in confinement operations. You do not want to overcrowd the water tank area.

Cool space. For animals in a pasture, provide shade. A shade cloth should be at least 8 feet off the ground for sufficient airflow. Orient shade either east-west or north-south. With an east-west positioning, the ground stays cooler but becomes muddy. North-south structures allow shade to move across the ground throughout the day. Or rotate animals to a pasture with natural shade such as trees or a lean-to.

If animals are in a barn, use ceiling vents and fans to circulate hot, humid air up and out of the barn. Also, consider sprinklers. However, do not use a mist as the water will not reach the skin for optimal cooling.

Animal handling. Livestock movement can create stress on the animal. During the summer months, work cattle, sheep or hogs in the early-morning or late-night hours. Avoid high heat times like 10 a.m. to 4 p.m.

Feed consumption. Animal body temperature increases after eating. Feeding at night or frequent, smaller portions can reduce instances of animals going off feed because of heat stress.

MU Extension beef specialist Eric Bailey stresses, if there one component from the list above to reduce heat stress, especially in cattle, it is water access. He says farmers should make plans to add extra tanks or get extra water to animals if the temperatures and humidity rise this summer.