Pigs typically don’t grow as fast and feed efficiency often takes a hit. Much of the downturn is linked to heat stress, which costs US pig farmers an estimated $900 million a year in revenues¹ - about twice the amount lost as a result of porcine reproductive and respiratory syndrome virus, Steven Pollmann, PhD, a livestock consultant and former president of western operations for Murphy-Brown LLC, a division of Smithfield Foods, told Pig Health Today.

These losses include impaired sow productivity as well as losses from grow-finish pigs. Pollmann estimates that, on average, producers lose $50 to $60 per animal each year due to heat stress.²

Pigs become susceptible to heat stress at about 70° F (21° C), he said. If temperatures stay at 80° F (27° C) or higher for several days, a myriad of negative effects will likely impact breeding herds, sows and pigs at the grow-finish stage of production.

‘Single biggest loss’

“Heat stress is far and away the single biggest loss we see,” Pollmann said. “It will have more impact on the industry than disease because…in the North American market, it will hit 95 percent of the herds.”

In addition, the estimated economic loss to producers does not include the lifelong impact on piglets born during these hot months.

For more than two decades, producers leaned on the feed additive ractopamine to optimize growth rate and feed conversion while increasing carcass leanness in grower pigs weighing more than 150 pounds. While the feed additive yielded benefits year-round, it was especially valuable to help offset losses associated with the traditional summer slow-down.

Now, with several major pork processors no longer accepting pigs fed ractopamine due to export requirements and consumer feedback,³ the challenge to maintain growth in summer is even greater. Producers are looking for alternatives to optimize growth and efficiency.

As the industry has evolved, so has the thinking on heat stress. Here are five management tools that can help producers increase growth and efficiency in summer months.

Optimise gut health

Stress, including heat stress, activates the animal’s natural flight-or-fight response needed for survival. But when stress becomes excessive or prolonged, it can cause inflammation and tissue damage. A major job of the gut is to maintain a protective barrier to keep out toxins and microorganisms. This gut barrier is maintained by a single layer of gut cells lining the intestine which are linked together by tight junctions, said Adam Moeser, DVM, PhD, associate professor of large-animal clinical sciences at Michigan State University, in a previous Pig Health Today article.

If the barrier gets damaged, protection is impaired, he said. The gut isn’t just responsible for nutrient absorption; it also plays a major role in immunity.

The gut barrier protects the host from toxins and microorganisms. However, if damaged, especially early in life, pigs can have compromised growth and disease susceptibility throughout the production period, based on Moeser’s research.⁴

It’s believed that more extensive damage to the intestine occurs if pigs are stressed at the time their gastrointestinal systems are developing. Stress, which includes weaning as well as excessive heat or mixing and crowding, activates the corticotropin-releasing factor, a stress hormone, which in turn causes excessive activation of mast cells - a type of immune cell.⁵

Bacitracin, a non-medically important feed medication with indications for increasing growth rate and feed conversion, has shown to be useful for maintaining performance in heat-stressed pigs. In studies conducted at North Carolina State University, investigators acclimated pigs to their respective treatment diets and rooms at 72° F (22° C) for 5 days. One-half of the pigs were kept for 10 days in temperatures of 96.8° F (36° C) for 12 hours and for the other 12 hours at 84.2° F (29° C) - the same heat stress pigs might encounter during hot summer months. The other half of the pigs were housed in a thermoneutral environment, meaning that ambient temperatures were maintained to prevent changes in metabolic heat production or evaporative heat loss.

In each environmental group, half of the pigs were fed bacitracin at the recommended dose while the other pigs were unmedicated. In both environments, pigs fed the non-medically important antimicrobial had better average daily gain (ADG) and lower feed-to-gain ratios despite heat-stress exposure compared to controls.⁶

Another finding of the study was that endotoxin levels were significantly lower (p < 0.05) in pigs fed the antimicrobial compared to unmedicated pigs.⁷ And in pigs subjected to mixing and crowding, a type of cytokine - a protein that causes inflammation - was significantly lower (p < 0.05) in pigs fed the antimicrobial compared to the unmedicated controls.⁸

In both studies, gut integrity was significantly better (p < 0.05) in the medicated versus unmedicated pigs.

Another study subjected pigs to both mixing and crowding. Once again, pigs fed the same non-medically important antimicrobial had better growth and feed conversion.⁹ Antimicrobials that are not considered by the Food and Drug Administration (FDA) to be medically important in human medicine do not require a veterinary feed directive.

Let boars be boars

Another effective way to improve growth in summer months is with immunocastration. This technology has been approved in the US since 2011 and is widely used by pork producers in more than 60 countries. It’s gaining traction in the US as a way to tap the naturally faster growth rate of intact males, which in turn leads to better feed conversion.

Indiana-based consultant Larry Rueff, DVM, who works with producers in the US and Asia, is using the technology, which involves a compound known as GNRF (gonadotropin-releasing factor analog-diphtheria toxoid conjugate).

Licensed for use in growing pigs by FDA, GNRF uses the pig’s immune system to reduce the production of androstenone and skatole, which are responsible for boar taint, the odor that emanates from heating pork from an intact boar marketed at weights exceeding 180 to 200 pounds.

The production efficiencies gained by allowing male pigs to remain intact means they eat less feed and produce less waste, creating the potential for an incremental reduction in the carbon footprint by as much as 3.6 percent (measured in CO₂ equivalent per kilogram of pig live weight) versus barrows.¹⁰

Housing 25 pigs per pen in 10 pens, Rueff moved them to finishing at 10 weeks of age and to market three months later. The first group of immunocastrates showed a 10 percent improvement in feed efficiency.¹¹

“That goes right into producers’ pockets,” Rueff said, referring to the feed savings. “It is sustainable; we’ve sustained it so far. We’ve always known boars convert feed faster than barrows. Immunocastration allows boars to express their natural physiological benefits.”

With some recent adjustments to the diets (such as increased lysine and phosphorous), the feed conversion has improved even more.

Rueff has collected performance data on immunocastrated pigs in over 12 groups since January 2014, and the numbers are promising. The last group of 250 that he ran through from wean to market had a feed conversion of 2.21 and ADG of 2.12 pounds per day.¹² They were marketed at 300 pounds.

“We have achieved two-tenths (0.2) of a pound improvement in feed conversion over good performing, conventionally castrated barrows,” he said.

Manage ventilation

“Make sure the basics are correct - the food, the water and the air,” said Emily McDowell, DVM, a veterinarian at Pipestone Veterinary Services in Pipestone, Minnesota, in a Pig Health Today report. “Make sure the water flow is good and the evaporative cooling sprinklers are set appropriately.”

Pollmann says the principal strategies for tackling heat stress must still apply. “Make sure the cooling systems are right, that there is enough ventilation and the pens are not overpopulated,” he said.

Jay Johnson, PhD, a research animal scientist with the USDA, specializes in stress physiology of swine. A study he helped conduct found an 11 percent reduction in air speed in the pen led to a 0.42° F increase in body temperature. That, in turn, was accompanied by an estimated 6 percent reduction in efficiency in the pigs, he added.¹³

“One of the simplest things to do is make sure ventilation and air speed are maintained,” Johnson said.

It might also be helpful to schedule feeding and other activities for the cooler hours.

Reducing the movement of the pigs during the hottest part of the day is a crucial part of combating heat stress. It is recommended that activities that disrupt pigs, such as feeding or checking the pens, be completed during the coolest times of the day.

Ten or 15 years ago, people believed problems created by heat stress could be resolved chiefly by engineering solutions, such as adequate ventilation and cooling pads. While that is still an important factor, other management tools are just as important in combating heat stress.

Monitor water

McDowell said producers should monitor their water sources daily, particularly when receiving new pigs from other farms. Before they arrive, make sure there is enough water and that all the sources are adequate and functioning properly, she recommended. She suggested one nipple waterer to 10 pigs in each pen, with a minimum flow rate of two cups (16 ounces) per minute for pigs that weigh less than 50 pounds and one quart per minute for larger pigs.¹⁴

Water quality also is critical. Sample water routinely to identify variations in minerals or bacteria.

Avoid crowding

“The balance between the number of pigs we’re trying to produce and the finishing space we have is still pretty much out of balance,” Pollmann said. He refers to “space balance” as an important factor to keep in mind.

“You’re increasing pigs per sow per year at the rate of 2.5 percent to 3 percent per year and your space stays the same for a period of time,” Pollmann said. “Then, you add space 3 to 5 years later. You’re always space short, and then we shake our head and say, ‘Why are pigs light going to market during the summer months?’

“In the truest sense, [immunocastration] could potentially give you 2 more weeks of finishing space, because the pigs are growing faster,” Pollmann said.

Most systems Pollmann has seen are short of finishing space. Typically, he said, a producer figures 11.5 wean-to-finish spaces per sow capacity.

“If somebody goes through that math and starts looking at it, generally they’re going to be somewhere between 8% to 10 percent short, and so you have that crowd capacity,” he added. “Then, when you get a little bit of a bump in fertility you’re trying to push more pigs through. This creates further crowding, thereby decreasing performance even more in a crowded system. On top of that, we’re taking pigs to heavier weights.”

Attention to detail

There’s truth in the adage, “It’s the little things that count,” and attention to detail will help you better manage heat stress. Train your staff to carefully check ventilation, water, nutrition, health and crowding, especially in warm summer months. Identify and control factors in grow-out and throughout the system to improve the predictability of the outcome, Pollmann said.

When factors like summer heat are out of your control, consider these management protocols to maximise performance and profitability.