by Two recently published studies are shedding new light on how the bodies of affected horses respond to feed. And this, the researchers say, will ultimately help fine-tune feeding recommendations for horses and ponies with ID. Amanda Adams, PhD, an associate professor at the Gluck Equine Research Center at the University of Kentucky (UK), along with then PhD candidate Erica Macon and the UK Aged Horse Research Center team, led the international effort to complete the studies, with support from MARS Horsecare™ and the Waltham Petcare Science Institute.
They collaborated closely with Patricia Harris, MA, PhD, Dipl. ECVCN, VetMB, MRCVS, Chief Scientific Officer at MARS Horsecare™ and Head of the WALTHAM™ Equine Studies Group, in Leicestershire, UK, and Simon Bailey, PhD, Dipl. ECVPT, FRCVS, Professor of Veterinary Biosciences and Head of the Department of Veterinary Biosciences at the University of Melbourne Veterinary School, Victoria, Australia.
Current challenges
“These studies really stem from the challenges we have all faced managing individual ID animals, as well as for me in particular with the ID horse herd in the UK, along with the questions we have received from countless horse owners asking questions. same questions: what and how do I feed my horse ID? says Adams.
Although horses with ID are often overweight or obese, the disease can also affect horses of healthy weight. Similarly, not all obese or overweight animals are ID. Therefore, bloodwork is absolutely critical in determining if a horse has ID. In affected horses, diagnostic tests will reveal elevated basal concentrations of insulin in their bloodstreams and/or abnormal bloodstream responses after consuming starch and sugar.
Both of these problems put equids at increased risk for founder.
But, says Bailey, “keeping insulin response at a moderate level after feeding ID animals will significantly help reduce the risk of laminitis.”
Adams says, to achieve this, his approach—and what he’s always recommended to owners—has been to “put them on diets low in NSCs (starch and water-soluble carbohydrates, collectively known as non-structural carbohydrates).”
But it always came back to the same question: what does a “low NSC diet” mean? Truly mean, since most research on insulin response to diet has been done in non-ID animals.
“It was always frustrating that while the anecdotal evidence largely supported the recommendations we were making, we still didn’t have any scientific data or research to back them up,” she says.
Meanwhile, Macon developed an interest in metabolic horses while completing his master’s research, which focused on differences in circulating protein concentrations between ID and non-ID horses. Hoping to continue this path, he sought out Adams in hopes of exploring whether proteins might be a significant driver of the insulin responses of ID horses.
“We decided it was finally time to start finding some answers,” says Adams.
What the studies have shown
First, the researchers compared how ID and non-ID horses (all weighing approximately 500 kilograms, or 1,100 pounds) responded to consuming a meal (about 600 grams, or 1.3 pounds) of four diets: three different restricted NSC foods with low, moderate, and high protein levels (to assess the potential role of protein in insulin responses) plus cracked corn with molasses.
In this study, protein content had no impact on how horses responded to eating a meal, the researchers found. As expected by the team, the non-ID horses’ insulin levels remained well within normal limits after they had eaten any of the feeds.
“But we were somewhat surprised at how quickly and how severely the insulin levels of ID horses increased, especially in some individuals after eating a relatively small meal of any of the feeds, compared to non-ID horses,” he says. Adams.
Based on these findings, the team wanted to confirm that the ID horses’ increased insulin levels weren’t just a response to eating, Adams says, since this hadn’t been studied previously. They followed up by evaluating how non-ID and severely ID horses responded to a variety of feeds, all fed at a rate of about 500 g (about 1.1 lbs) for a 500-kilogram horse. The diets included a high-protein NSC ration balancer, cracked corn with molasses, steamed flaked corn with molasses, hulled oats, and a customized ultra-low NSC feed produced specifically for the study by BUCKEYE™ Nutrition.
They found that the ID horses’ insulin responses after consuming the low-NSC feed were significantly lower than when they ate the other diets, “which we were very pleased to see,” says Adams.
“If the feed they consumed had a sufficiently low level of NSCs, they did not respond to the same degree; their responses seemed more similar to the responses of non-ID horses, although they may have come from a higher starting point,” she says. “This confirmed that it wasn’t just the act of eating that induces an insulin response.
“Of course,” he adds, “that begged the question: What’s the threshold for ‘low enough’?”
To find out, the team assessed how the bodies of ID horses responded to eight feeds with a similar baseline but varying NSC levels.
“I spent an entire year sitting at the lab bench with a coffee grinder,” says Macon. “I made a new diet every week using mixes of different feeds to get varying amounts of NSC, and then shipped to the lab. We finally decided to add specific amounts of pure starch and sugar to the baseline diet so we could get the levels just right.
Once the horses consumed the different diets, the team sent in blood samples to evaluate insulin responses.
“Every time I got a new set of results, I crossed my fingers, toes, and eyeballs that it would be within the range I needed,” she says. “One day, they were!”
They found that the threshold appeared to be less than 0.1 g NSC/kg bw/meal. Additionally, the horses’ insulin levels were more likely to rise significantly.
“There’s a lot of variation in how individuals respond,” Harris notes, “and some horses and ponies will have a different threshold. Of course, any such threshold will depend on how low an insulin response is actually required, as none of the animals in our studies developed any clinical problems.”
More research is needed, he adds.
“These studies are therefore the first in a series that we hope will help put the science behind how we feed ID horses,” Adams says.
She and her colleagues are currently working on additional research to answer other common questions, such as how ID horses respond to small amounts of feed containing higher NSCs and to larger amounts of products providing lower NSCs.
The research team is also conducting similar studies using hay pellets and long-stemmed forage to better understand how ID horses respond to help develop threshold guidelines. All of this will improve the way owners around the world can keep their ID horses healthy and happy.
“This work is important in giving us more evidence to make more effective recommendations,” says Bailey.
Adams adds, “The ultimate goal is to run these horses on a low NSC diet (both forage and feed), but we have yet to determine what that means and how much low NSC is needed in different clinical situations so that horses do not have an inappropriate insulin response.”
Feeding per hour
For now, owners of affected horses can keep them on track by relying on a diet of low-NSC forage (ideally less than 10 percent NSC on a dry matter basis), he says, and many horses can be managed well. just with such a forage and forage balancer. Harris recommends that owners of horses with severe ID divide a low NSC ration balancer into several meals per day.
“Since dietary insulin response is variable and we do not know all nutritional triggers, it is advisable to monitor an individual horse or pony’s response to its specific diet (both feed and forage) if it is deemed essential to induce only a low insulin response.” Harris points out.
Therefore, adds Adams, “it’s important that you work closely with your veterinarian (who, in turn, will work closely with their diagnostic lab) and your nutritional consultant.”
