High-Starch Meals Induce Systemic Inflammation in Older, Heavier Horses

Younger age and lower body condition appear to protect horses against occasional spikes in nonstructural carbohydrate consumption.
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High-Starch Meals Induce Systemic Inflammation in Older, Heavier Horses
Older and overweight study horses had increased IL-1β levels after consuming high-starch diets. | istock.com
Horses consuming high-starch meals experience elevated levels of circulating interleukin 1b (IL-1b)—a potent proinflammatory mediator. This might be particularly problematic in older and overweight horses, which have higher inflammatory protein levels in their resting state. In a new study that married those two scenarios, researchers from Sam Houston State University, in Huntsville, Texas, found that both overweight and older horses had elevated IL-1b levels after consuming high-starch meals. This finding was not unexpected but suggests that older and overconditioned horses might benefit from diets lower in starch and sugar.

In their study the team conducted two feeding trials to evaluate age and body condition’s effects on a horse’s response to high-starch meals.

Trial 1: Effect of Body Condition on Inflammation

In the first trial the researchers divided middle aged horses (10-17 years) into two groups: Those with body condition scores (BCS) of 4 to 5 (ideal BCS), and those with scores of 6.5 to 8 (overweight). All horses had free access to hay, salt, and water and were fed steam-rolled barley (SRB) to provide 1.2 grams of nonstructural carbohydrates (NSC, starches and sugar) per kilogram of body weight. This NSC amount has been previously shown to induce a postprandial (after a meal) rise in circulating IL-1β.

On Day 14 of the study, following an overnight fast, the researchers collected blood samples 30 minutes prior to and one, four, and eight hours after an SRB meal. They evaluated IL-1β values in the horses’ blood as a measure of systemwide inflammation.

“We found that overweight horses had an immediate postprandial increase in IL-1β after being offered a high-starch meal,” said Jessica Suagee-Bedore, PhD. “In contrast, horses with an ideal BCS only had elevated levels of IL-1 β after 14 days of the high-starch diet.”

Now an associate professor of practice in animal and poultry sciences at Virginia Tech, in Blacksburg, Suagee-Bedore conducted this research as an assistant professor in Sam Houston’s School of Agricultural Sciences, College of Science and Engineering Technology.

Suagee-Bedore also reported that mean IL-1β concentrations increased from Day 1 to 14 in the lean horses.

“Thus, even horses with healthy body weights begin to show signs of systemic inflammation after regular exposure to high-starch/sugar meals,” she said.

Trial 2: Effect of Age on Inflammation

In this phase of the study, six horses with body condition scores of 5 to 6 were split into two groups based on age: old (20-23 years) and middle age (12-14 years). All horses were fed hay at 2% of their body weight and had free access to salt and water. In addition, they received SRB at a rate of 1.2 grams of NSC per kilogram body weight per day followed by a commercial concentrate at 0.5% bodyweight. The SRB was fed for 36 days. After an overnight fast, the researchers collected blood samples two hours after the SRB meal to measure IL-1β.

“Older horses had enhanced IL-1β levels after 36 days of a high-starch diet,” said Suagee-Bedore. “This confirms previous reported data and could be explained by older horses having chronic stimulation of the immune system throughout their life span or a reduced capacity of older individuals to differentiate between the severity of signals that activate inflammation.”

Together, these trial results confirmed the researchers’ hypothesis that systemic inflammation occurs in older and overweight horses after consuming diets high in NSCs.

“While this inflammatory response appears to occur quickly, almost immediately in fact, in older and overweight horses, younger and leaner horses appear to require repeat exposure before this inflammatory response is appreciated,” Suagee-Bedore said. “Thus, younger age and leanness appear to protect horses against occasional spikes in NSC consumption.”

The next steps, she added, are to determine the downstream effects of the observed elevated IL-1β levels and to evaluate the signals involved in stimulating IL-1β production in response to diet—a process believed to involve a proteinaceous structure called the inflammasome.

Suagee-Bedore said IL-1β has received little attention in horses, despite researchers on previous studies reporting increased production during laminitis and in damaged cartilage during arthritis progression.

“I think our next question needs to be whether inflammation, activated in one area of the body, can prime another part of the body to fail more quickly in the face of an inflammatory stimuli—like setting up dominoes to fall,” she said.

In humans, researchers on some recent studies related systemic inflammation, specifically that of IL-1β, with neuroinflammation that contributes to Alzheimer’s disease, said Suagee-Bedore. Other data suggest that diet can activate systemic IL-1β in humans.

“Because we see increased blood concentrations of IL-1β in response to these high-NSC diets in horses, I think we should investigate potential relationships between systemic low-grade inflammation and other chronic inflammatory diseases that are so prevalent in horses,” Suagee-Bedore stated.

The study, “Age and body condition influence the post-prandial interleukin-1β response to a high-starch meal in horses,” was published in Animals (Besel) in November 2021.

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Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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