Heat stress can result in significant economic costs to your livestock operation. For example, it is estimated that the annual cost of heat stress in the U.S. swine industry is $900 million (Pollmann, 2013). Of that, about $450 million is in the grow-finish stage and about $450 million is in the breeding herd.
Based on these estimates, it should come as no surprise that investments in on-farm cooling systems are highly prevalent. However, cooling systems may not always be economically feasible and mechanical failure can cause unplanned heat-stress events.
Heat Stress: What’s Happening Inside the Animal?
When an animal experiences heat stress, its core body temperature increases causing blood flow to be diverted from visceral tissue — tissue that lines the blood vessels, stomach, digestive tract and other internal organs — to the skin surface to increase heat dissipation. As blood flow is reduced to the visceral tissue, this causes a reduction in the amount of oxygen (hypoxia) and energy available to the enterocytes (single layer of epithelial cells) lining the intestinal tract. When this occurs, tight junctions that hold the enterocytes together can weaken, allowing pathogens and their toxins to transfer into the bloodstream, ultimately leading to a condition called leaky gut.
With the onset of heat stress, we know animals often experience a marked reduction in feed intake, which has been hypothesized as a mechanism to help reduce metabolic heat. While a large contributor to lost performance under heat stress, this reduction in feed intake may only partially explain why animals under heat stress have decreased performance.
In addition, a higher respiration rate from the animals trying to cool themselves results in the production of oxygen and nitrogenous free radicals, which can weaken or destroy the intestine’s tight junctions. Severe heat stress may lead to morphological changes in the intestine, such as decreased gut villi height, greater gut villi width and potentially a breakdown of the tight junctions of the enterocytes. The intestine may become vulnerable to transfer of lipopolysaccharides (LPS), or endotoxins, across the intestinal wall and into circulation causing immune system activation.
Zinc: A Key Trace Mineral For Tight Junctions
Several research studies have established that the trace mineral zinc plays a key role in maintaining intestinal integrity by strengthening the tight junctions during challenges. Research has shown that zinc upregulates tight junction proteins and heat shock proteins. Furthermore, zinc is an antioxidant, and oxidative stress may play a key role in initiating leaky gut. The research has also shown that the form of zinc fed influences its effectiveness at reducing leaky gut.
Iowa State University conducted a study to demonstrate how acute heat stress conditions contribute to leaky gut. Results showed that feeding performance trace minerals such as Availa® Zn helps decrease the occurrence of leaky gut by improving the viability and integrity of the intestinal system.
In this study, thirty-two crossbred pigs with an initial weight of 63 kg (140 pounds) were randomly assigned to one of four treatments:
- Treatment 1 (Thermo-Neutral Control): 120 ppm of zinc sulfate fed in thermo-neutral conditions (21°C; 70% humidity); ad libitum feed intake.
- Treatment 2 (Nutrient-restricted Thermo-Neutral Control): 120 ppm of zinc sulfate fed in thermo-neutral conditions (21°C; 70% humidity); restricted fed intake. Animals in this treatment were allowed to consume the same amount of feed as the two heat-stress diets (Treatments 3 and 4, 17% of ad libitum feed intake); this allows for comparisons in a controlled environment.
- Treatment 3 (Heat Stress Control): 120 ppm of zinc sulfate fed in acute heat-stress conditions (37°C, 40% humidity); ad libitum feed intake.
- Treatment 4 (Heat Stress Availa Zn): 120 ppm of total zinc supplemented (60 ppm zinc from Availa Zn and 60 ppm of zinc sulfate) in acute heat-stress conditions (37°C; 40% humidity); ad libitum feed intake.
As expected, subjecting pigs to acute heat-stress conditions resulted in increased rectal temperatures, increased respiration rates and reduced feed intakes. However, the research also sheds light on what’s happening inside the pigs during an acute heat-stress challenge.
Researchers measured ileal permeability — the third and final part of the small intestine — from harvested pigs. Pigs in the heat-stress conditions of Treatment 3 and the pair-fed thermal-neutral conditions of Treatment 2 showed greater gut permeability compared to pigs in the thermal-neutral conditions of Treatment 1. This finding indicates that a heat-stress event, or even a period when animals are under restricted feed intake, such as out of feed events, (pair-fed Treatment 2), increases the risk for intestinal permeability (leaky gut).
When the pigs were subjected to acute heat-stress conditions, feeding Availa Zn helped decrease gut leakage compared to feeding inorganic zinc sulfate. Pigs fed Availa Zn were able to mount a more effective immune response. Among heat-stressed pigs, those receiving Availa Zn expressed greater concentrations of plasma lipopolysaccharide (LPS) binding protein compared to those receiving zinc sulfate. As an acute-phase protein, LPS binding protein sequesters bacterial LPS so that bacterial LPS can be destroyed by other immune components. Within heat-stress treatments, pigs fed Availa Zn (Treatment 4) had numerically lower serum endotoxin levels compared to pigs fed zinc sulfate (Treatment 3).
Heat Stress and Performance Trace Minerals: Bringing It All Together
Heat stress is a widespread issue that swine producers need to manage. It’s critical to have a plan in place prior to the onset of hot weather conditions to prevent the long-term effects heat stress can have on animal performance. By incorporating performance trace minerals like Availa Zn into swine diets, animals are better able to reduce the impact of leaky gut during heat stress conditions.
Research demonstrates the source of zinc fed in swine diets is critical for mitigating heat stress. Contact your Zinpro representative to learn more about the benefits of feeding Availa Zn in swine diets to help manage heat stress and inflammation.