We might be feeding our horses too well, at least as far as predisposing them to laminitis. Ray J. Geor, BVSc, PhD, Dipl. ACVIM, professor and chair of the Department of Large Animal Clinical Sciences at Michigan State University, spoke about controlling nutritional risks in pre- and post-laminitic horses at the Sept. 17-18 Laminitis West Conference in Monterey, Calif.
"All of us recognize that horses evolved to consume roughage," said Geor. "Despite the fact that we're all well aware of that, we tend to feed horses somewhat differently. We often feed them starch-based meals (cereal grains and sweet feeds, for example) or allow them to graze 'improved pastures' that are rich in sugars."
Pastures designed for dairy cattle, for example, have a much higher carbohydrate content than is ideal for horses. Overconsumption of these types of feeds can lead to laminitis, especially in horses and ponies with equine metabolic syndrome (EMS). Changes in pasture, like that which occurs in spring and fall when the water-soluble carbohydrate (WSC) and starch contents rise, pose the greatest risk for an episode of laminitis.
Consumption of pasture rich in WSC can markedly disturb the microbial population of the horse's hindgut and trigger events that lead to the development of laminitis. Yet not all horses turned out on WSC-rich pasture will develop laminitis. Geor explained that horses and ponies with features of EMS appear to be more susceptible to laminitis under these conditions. Clinical features of EMS include obesity and/or regional accumulations of excessive fat (e.g., a cresty neck) and insulin resistance. In these animals, exaggerated increases in blood insulin after feeding might contribute to laminitis.
"So the first step in lowering risk for laminitis is to identify these high-risk animals before they become a proverbial 'train wreck,'" said Geor. "Secondly, we've got to do a better job in terms of managing carbohydrate nutrition in these high-risk horses and ponies."
Geor emphasized three key concepts related to risk of nutrition-related laminitis:
1. Substantial flow of rapidly fermentable carbohydrate (i.e., starch and WSC) to the hindgut can occur with grain feeding and pasture grazing under certain conditions, leading to changes to and instability of the microbial community living in the hindgut. Reduction in the size of grain and grain-based meals and restricted access to pasture at certain times of the year can help reduce diet-associated disturbances in hindgut function.
2. Dietary starches and WSC markedly affect blood-insulin responses, and equids with EMS tend to have exaggerated responses. Very high blood insulin is one factor that contributes to development of laminitis in EMS animals.
3. Seasonal factors can modify the risk for nutritionally associated laminitis through effects on appetite, adipose (fat tissue) mass, insulin sensitivity, and the dynamics of blood insulin.
Geor said researchers are just beginning to recognize these seasonal risks.
"Horses and ponies are seasonal animals," he said. "They're designed to gain weight during the summer and into the fall and to lose weight during the winter. The question remains whether or not our modern management techniques interrupt that natural, seasonal cycle and contribute to obesity, which then contributes to insulin resistance."
Geor speculated that insulin-resistant animals might lack the flexibility to adapt to changes in dietary conditions (e.g., seasonal changes in pasture), and this plays a role in their susceptibility to laminitis.
He concluded his talk with the take-home messages that carbohydrate nutrition is strongly linked to laminitis risk, and that strict management of carbohydrate nutrition is indicated for equids with an insulin-resistant phenotype (i.e., EMS).
Photos: Ray J. Geor, BVSc, PhD, Dipl. ACVIM, professor and chair of the Department of Large Animal Clinical Sciences at Michigan State University; laminitis poster