“We are looking at an extended period of heat stress, beginning July 15,” said Matthew Dixon, meteorologist for the University of Kentucky College of Agriculture, Food and Environment. “Daily temperatures in the low to middle 90s will be common through at least the weekend. These conditions will push livestock heat stress index into the danger to emergency categories during the afternoon and evening hours.”
The combination of heat and humidity can cause concern for livestock.
“The livestock heat stress index helps us determine what level of concern farmers and pet owners need to have for their animals,” said Dixon. “That index helps producers know when heat stress could create a problem for their animals, so they can be even more vigilant in making sure they have the necessary resources to combat the stress.”
Many livestock producers are familiar with the steps they need to take to help animals endure these dangerous conditions.
“The most important thing producers can do is provide cool, clean water and shade,” said Jeff Lehmkuhler, UK beef specialist. “It’s also a good idea to avoid working or transporting animals during periods of danger or emergency heat stress. Make sure cattle have access to shade.”
Horses have difficulty regulating their body temperature when temperatures exceed 90 degrees. If humidity is high, the temperature doesn’t even have to reach 90 degrees to make life uncomfortable for horses. Unlike cattle, horses do sweat, but if the humidity is high, they may not cool as efficiently as normal.
“Horse owners can reduce heat stress by scheduling activities during the cooler part of the day and making sure horses have plenty of water,” said Bob Coleman, UK equine extension specialist. “If you do transport horses during the cooler part of the day, give water before, during and after transportation to reduce the risk of dehydration.”
Coleman added that even non-working horses will double their water intake during hot weather. Owners should allow them to drink often to help maintain water balance.
“If you let them drink often, it can relieve the horse’s urge to drink a lot of water after exercise, and they need to gradually drink after a workout,” he said. “Also, remember lactating mares have special water requirements, because they are using water for milk production as well as body temperature regulation.”
Hot weather also increases horses’ need for salt, because they lose the mineral during sweating.
Cattle can be particularly susceptible to heat stress because they are not able to sweat effectively, which means they must rely on respiration to try and dissipate heat.
“A common sign that cattle are experiencing heat stress is excessive panting and increased respiratory rate,” said Katie VanValin, beef specialist at the UK Research and Education Center in Princeton. “There are a multitude of factors that determine how susceptible an animal is to heat stress, including breed, stage of production, age and hair coat color. Heat stress results in decreased growth and reproductive performance and even death in severe cases.”
For dairy cattle, it is important to keep buildings as open as possible to allow air to circulate. Fans can make a big difference, and sprinkler systems that periodically spray a cool mist on the animals are also beneficial.
Poultry are especially prone to heat stress. Mortality during extreme heat can be significant, and egg production and hatching rates can drop.
“Since the birds don’t have sweat glands to help get rid of excess body heat, they have to pant to cool down,” said Jacquie Jacob, UK poultry project extension manager. “It’s important to make sure chickens are in well-ventilated areas and they have access to clean, cool water at all times.”
On the crop side of things, about a third of Kentucky corn crop is in the silking stage, with the other two-thirds probably pollinating in the next week or two.
“Most of the corn will experience very high temperatures when it is most sensitive to drought and other stresses,” said Chad Lee, extension professor and director of the UK Grain and Forage Center of Excellence. “Everything hinges on favorable conditions for about a three-week period and more specifically on the week that a corn plant pollinates. Enough water during seed fill is critical as well, but we must get the kernels established before they can be filled.”
Corn’s defense against warm weather is that any single plant will drop most pollen during the morning and will drop less pollen later in the afternoon/evening, thus, avoiding the hottest part of the day. Adequate water and relative humidity will help. Heat can quickly dry out the pollen grains.
“Temperatures above 90 are detrimental to pollen,” Lee said. “The heat also can dry out the silks. If the pollen and/or silks are dry, pollination will not occur. Back in 2012, extremely hot mornings combined with low humidity and dry soils all conspired to damage pollination Even with the forecasts, 2020 is in a much better situation than 2012, but there are risks to pollination in 2020.”
Temperatures above 86 put added stress on corn plants and usually increases water demand.
“In a ‘normal year,’ a corn plant at peak water demand usually requires about 0.3 inches of water per day. If temperatures are in the upper 90s, water demand will be greater,” Lee said. “We may get good pollination because of pollen drop in the mornings and because of relative humidity, but the heat will remove some yield potential from the plants.”
Dixon said long-range outlooks hint this warm and humid pattern will continue into next week.
The UK Agricultural Weather Center provides statewide and county-specific weather information, alerts, livestock heat stress conditions and more. To view the index for a specific location, go to or click a specific location from the Kentucky map at http://weather.uky.edu.