Heat stresses livestock; production can decrease when temperatures increase When heat indexes approach the 90 degree Fahrenheit mark, heat stress becomes a concern, said Brad Johnson, Extension feedlot specialist at South Dakota State University.
Several Extension specialists gave their comments on heat stress in various livestock species.
"Heat stress is very common (in feedlot cattle) as temperature's go above 90 degrees and, more importantly, the humidity and the heat index gets above 90 and 95 degrees," he said.
The first sign of heat stress in cattle is labored breathing. Cattle will also seek out water and have higher amounts of water intake, said Johnson.
In dairy cattle, heat stress becomes a problem anywhere above 77 to 78 degrees F, said Dave Weinand, Extension dairy specialist at SDSU. "Above that, cows start to decrease intakes, with decreased intakes comes decreased milk production. There's also decreased fertility and decreased immune systems," he said.
Although hogs are fairly resistant to heat stress, when it does occur, reproductive capability really suffers, said Jeff Clapper, Extension swine specialist at SDSU. This is of special concern in swine because they are polyestrous animals and breed year-round.
In the boar, heat stress can decrease libido and decrease or completely stop spermatogenesis.
"If there's an increase in internal body temperature by one degree Fahrenheit for three days, it will entirely disrupt the spermatogenic cycle and the producer won't see these effects until 15 to 30 days later when sperm numbers begin to drop and they'll last up to 50 to 60 days," noted Clapper.
The specialist suggests producers breed extra females to make up for the decreased conception rate that occurs during the hot months of June, July, and August.
Heat stress is particularly dangerous two times during the breeding cycle for sows: right before the time of breeding and late in pregnancy.
An increase in internal body temperature at the time of breeding and during the beginning of pregnancy will suppress estrous expression and cause embryonic loss, he said.
Symptoms of heat stress in swine are decreased feed intake, lethargy, and panting. Internal body temperature rises in extreme cases.
"They're probably smarter than you and I because they'll just lay around and won't do anything to generate any more heat," said Clapper.
In all three species, decreased dry matter intake is a cause for concern. Depending upon the degree of heat stress, up to a 30 percent reduction of dry matter intake can occur, said Johnson.
Weinand explained cow psychology, "If the cow doesn't feel good, she doesn't eat. It's the same with us. If we don't feel well, we're going to decrease how much we eat during the course of the day."
"The first calories consumed go to maintenance, and if the cattle do not eat enough above maintenance requirements, they won't gain at all," added Johnson.
As with humans, water is an important component in preventing heat stress. In addition to having water available, the quality of that nutrient is key. "If you wouldn't drink from the water, odds are the (animal) probably doesn't want to either," said Weinand.
Another tool for dealing with heat stress is adjusting feeding times with the outside temperature. Feed early in the morning or late in the afternoon or early
evening when temperatures are at their lowest. "That's when the cattle will be up to the feed bunk and be willing to eat more," said Weinand.
Another short-term relief effort is sprinkling or misting water on cattle or swine, either with a permanent sprinkler system or manually spraying the animals with a garden hose or lawn sprinkler.
"If you can keep the pig's head cool, it thinks the rest of the body is cool and it will adjust accordingly," remarked Clapper.
Even running water on the ground so cattle can stand in the water for a time will help alleviate the heat stress, said Johnson.
However, he cautions that if water runs into a low spot and develops into a pool, it may be a problem getting the cattle out of it and up to the bunk to eat. Johnson prefers running water on a cement pad so the cattle can at least wet the bottoms of their hooves.
Additional considerations when sprinkling cattle in an indoor setting are water placement and disposal and air circulation.
"It's ultimately important that you completely wet the back of the animal, but do not get any water near or around the bedding or feed," said Weinand. "You not only need the water, but need the fans to dry the cows off."
He also reminds producers they need a basin or some other place for the extra water to collect.
Reducing overcrowding, both in the barn and the feedlot, can also reduce heat stress. Weinand said many free-stall dairy barns are anywhere from five to 10 percent overcrowded. Producers should decrease crowding during the summer months or make additional plans for outside housing for the later lactation cows.
"Increase their surface area so the air can move around and through those cows so they get cooled off," he said.
Johnson recommends 20 square feet of shade per head of cattle. A survey administered by Iowa State University during a severe heat stress outbreak found feedlots with severe death loss � greater that 5 percent in a two-day period–had less than nine-tenths of a square foot of shade per head. Feedlots that experienced very little death loss had close to 19 square feet of shade per head.
Shade can come from trees, a windbreak, or a barn. Anything that will get the cattle in out of the sun, said Johnson.
Long-term solutions available to producers are the direction of slope in a feedlot pen and the addition of fans in a barn.
A consideration when building new feedlot pens is slope. "When the sun beats down in the late afternoon in the southwest part of a pen, if the cattle are lying on a mound that is facing the southwest, they're more susceptible (to heat stress) than cattle in facilities sloped to the east or southeast," he said.
Increasing ventilation in a barn can be achieved by several methods. In stall barns, mixing fans can keep the air moving. The next step up would be tunnel ventilation which pulls air from one end of a barn, across the animals, and exits at the other end.
Weinand recommends utilizing tunnel ventilation only during summer months because of the amount of cold air pulled in by the system in the winter.
Fans require some maintenance. Dust, corrosion, and rust can decrease fan efficiency by at least 20 to 30 percent, warned Weinand.
For more information on heat stress, contact your local Extension educator.