Research shows negative effects of heat stress in gestation linger in growing pigs.


Regardless of the production stage, heat stress can cause negative outcomes for pigs. In growing pigs, the most likely impact is reduced feed intake and efficiency. It can cause delayed puberty in replacement gilts and increase mortality in farrowing sows. In the lactating sow, a drop in feed intake risks her milk production, body condition and future reproductive performance, not to mention her litter’s growth. In the gestating sow, heat stress in early gestation can result in a lost pregnancy; in late gestation, it can cause stillbirths.


But those are the more obvious or direct effects of heat stress, and past research has shown that the direct negative effects of heat stress cost the industry as much as $900 million annually.


“We’ve seen there are indirect or delayed consequences that begin in gestation,” says Jason Ross, associate professor and director of the Iowa Pork Industry Center, Iowa State University (ISU). “Heat stress is costing us more than we realize.”


To learn more, ISU researchers outlined an investigation into the heat-stress impact on gestating sows and their eventual offspring. They secured a $2.5 million USDA grant in 2010, which eventually spun into a series of collaborative research efforts involving multiple institutions — ISU, University of Missouri, Virginia Tech University, as well as USDA’s Agricultural Research Service (ARS) and Purdue University. The National Pork Board provided additional funding and the research has continued.

In Utero Heat Stress

The research began at the University of Missouri where gestating sows, typical of today’s highly prolific commercial genetic lines, encountered either a thermal-neutral environment or heat stress between day 30 and 60 of gestation for as many as 30 days. To mimic the real world, sows were exposed to a cyclical heat stress, says Jay Johnson, research animal scientist, USDA ARS, who was involved with the ISU research. “It was only acute heat stress for part of the day. The rest of the time, the sows were exposed to a mild heat stress,” he notes. “We need to know more about the timing and exposure, but it is possible that a shorter exposure to heat stress could induce negative effects on the piglets.”


Some of the progeny were shipped to ISU for growth- and production-related analysis, while some of the gilts headed to Virginia Tech for reproductive experiments. It’s worth noting that the growing-pig results obtained in a university setting have been replicated. The Australian hog industry also has verified the negative impact of in utero heat stress on future production traits.


Impact on the Growing Pig

In some respects, the researchers are just scratching the surface, but the evidence is compelling. According to Lance Baumgard, professor at ISU, and Johnson, if a sow is heat stressed while pregnant, the following occur in her offspring.

• The in utero heat-stressed offspring have an increased body temperature setpoint compared to the thermal-neutral offspring. “This increased body temperature (thermal energy) comes at a cost, as that thermal energy likely comes from feed energy,” Baumgard notes.

• Maintenance of that higher body temperature requires an increase in metabolic heat production, which increases the pig’s maintenance cost by as much as 12 percent to 14 percent. This is further verified by alterations in thyroid-hormone production, which affects post-natal metabolism.

• The higher body temperature “might also increase the pigs’ heat-stress susceptibility because it may decrease their thermal gradient and ability to dissipate heat,” Johnson adds.

• They have increased circulating insulin levels their whole life, which causes them to accumulate more adipose (fat) tissue. “Thus, the pig derived from a heat-stressed sow partitions more nutrients toward fat and less toward muscle,” Baumgard notes. In fact, heat-stressed piglets have an increased ratio of fat to protein/lean-muscle deposition.

• Feed efficiency for in utero heat-stressed offspring declined by 11 percent. “This negatively impacts the time it takes to reach market weight and the feed costs to get them there,” Baumgard adds.


The search for answers continues. Johnson’s ARS lab is looking into whether the in utero heat-stressed pigs are more sensitive to stressors later in life. “We’re getting a preliminary indication that when these pigs are weaned and transported, their stress responses are somewhat altered,” he says.


Researchers want to further quantify the economic impact of the indirect effects of in utero heat stress, as well as learn more about how it affects carcass composition. They also want to know if there is a window where heat stress in gestation has more/less impact on the litter.


Impact on Breeding Prospects

More research is needed on the in utero heat-stress impact on replacement gilts. Virginia Tech researchers found that the heat-stressed offspring recorded performance differences that numerically favored the thermal-neutral pigs, but statistical differences were not as evident.


“The heat-stressed gilts ate more but recorded similar body-condition scores and weight,” says Tim Safranski, swine specialist, University of Missouri. “Once farrowed, those gilts did record statistically lower piglet survival rates (0.08).”


Purdue University researchers have looked at a limited number of young boar pigs and found that heat stress in gestation reduced their sperm production. This study is scheduled to be repeated.


“We need to look at the gilt’s development, including ovaries,” Safranski adds. “If in utero heat stress affects the boars, it probably affects gilts too.”


Gestation heat stress may be one more topic to discuss with your replacement-gilt supplier. You already ask about health, genetics, and reproductive and production performance, but what sort of thermal and social environments do the replacements encounter? If you’re a gilt multiplier, these are even more critical considerations.


“If replacement gilts and boars are born in September, they could have been exposed to heat stress in utero. Then the gilts enter their first cycle during the summer, which is prime time to encounter heat stress again,” Johnson notes.


Take-home Points

“We have determined that heat stress in the sow does have a significant, negative, life-long impact on her pigs,” Johnson says. “It has a lot of consequences on productivity, well-being and, potentially, economically.”


His advice is to focus on preventing heat stress. Make sure you implement proper sow-management and cooling strategies. It might require making some changes and updates in the barns. “There are a lot of technologies available, and we continue to learn more,” Johnson says. He points to research underway at Purdue University that suggests cool pads for sows may offer promising results.


This in utero heat-stress research is an example of doing the investigations today so that you have answers for tomorrow. Scientists agree that rising temperatures and longer periods of higher temperatures will continue to challenge the management and heat-stress mitigation strategies for pork producers.


“Not only is climate change going to be a bigger issue going forward, but will we continue to have access to the water and energy we need to produce pork and to feed 9 billion people?” Safranski says. “Studying the broader impacts of heat stress helps us better understand how to produce a consistent product efficiently.”


Don’t Wait for Temps to Rise

“The goal is to identify and fix heat stress before it gets to be a problem,” says Tim Safranski, swine specialist, University of Missouri. “A pig has limited options to deal with heat.”


An adult pig’s thermal-neutral zone is 50° F to 70° F. Of course, air humidity impacts the animal’s temperature tolerance. Normal rectal temperature of a sow is 100.5° F to 103° F.


A sow’s neutral respiration rate is 15 to 25 breaths per minute. At 30 breaths, she’s starting to show stress. “At 60 breaths, she’s doing all she can to manage the heat,” he adds. “Teach workers to observe behavioral factors, such as the sow’s posture and breathing, and intervene when necessary.”-


Safranski offers these action items to be prepared for the warmer temps to come.

• Check cooling systems long before they’re needed. Make sure misters, drippers and cool cells are clog-free and working properly.

• Ensure that curtains don’t have holes or leaks that will short-circuit air flow. An open door will disrupt air flow too.

• Clean fans — dust can reduce efficiency by 40 percent. Check the tension on belts. Make this a monthly task.

• Add stir-fans to move air in areas of the barn that are perpetually warmer.

• Move pigs during the cooler part of the day.

• Consider different feeding options — wet feeding, feeding at night or early morning.

• Check the functionality of waterers and flow rates. Make sure there’s always enough cool water available.

• In the farrowing room, switch to low-watt heat lamps and place them so they’re not shining on the sow.

• Give extra attention to parity-1 gilts. “There’s a larger heat-stress impact on them versus multi-parity sows,” he
adds. “There is a lot of heat associated with metabolism — with life functions, milk production and fetus development. The parity-1 female is still growing so she produces more heat.” Consider placing parity-1 females in cooler locations in the gestation barn, such as near the cool cell.


“For the maintenance tasks, make it someone’s responsibility and put it on the calendar,” Safranski adds.


Frank’s Note

Heat stress is one of the many issues that producers have to tackle. In this Progressive Pork we look at some of the impact of heat stress.


Farmweld’s commitment to providing solutions has led to improving our product line to address heat-stress related issues. A prime example is the Farmweld Modular Cast Center Platform and the Farmweld Warming Panel™, which help establish micro-environments within the farrowing crate and creep area. These products allow you to meet both the sow’s and piglets’ very different thermal-comfort zones.


The durable Modular Cast Center Platform features cast iron with fiberglass beams to provide a cool, comfortable surface for the sow. Placed in the creep area, the Farmweld Warming Panel reduces drafts to keep newborn piglets warm and draw them away from the sow to sleep.


Farmweld also offers a range of waterer options to accommodate all areas of production and types of management preferences. We have troughs for use in the gestation facility, cups that meet the needs of nursery and wean-to-finish pigs and wet/dry feeders for use with sows and/or growing pigs.


Warm temperatures are coming, and you want to be prepared to ensure that pigs don’t face the negative consequences of heat stress. Farmweld can offer guidance, whether you’re looking to identify feeding and watering options that keep your pigs eating or pen designs that best accommodate air circulation and pig comfort.


If you have questions, don’t hesitate to call us at 1-800-EAT-PORK (328-7675) or use the contact form or LiveChat on our website.


Frank Brummer, President, Farmweld, Inc.


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