Horses and high-starch diets generally don’t mix well. Not only has this type of diet been shown to disturb the composition and activity of the gut microbiota, increasing a horse’s risk of colic, but it might also affect behavior, according to the results of a recent study.

“Because it is known that intestinal microbiota can interact with the nervous system, modification of the microbiota may directly alter behavior,” noted Alexandra Destrez, PhD, Lecturer at AgroSup Dijon (UMR Metafort), in France.

To investigate the extent to which intestinal stress caused by a high-starch diet is associated with behavioral changes, the researchers employed six healthy geldings which had previously been affixed with a fistula (surgically-created passageway to digestive system). The horses were fed two energy-equivalent diets twice daily over three three-week periods (with a five-day transition period between Periods 1 and 2). Diet H was comprised of 100% hay (Periods 1 and 3) and Diet HB included 57% hay and 43% barley (the high-starch diet, Period 2).

To monitor the diets’ effects on horses’ physiological status, researchers collected blood samples during the second week of each period and cecal and colonic samples during the third week of each period. And, to analyze behavior changes over the course of the study, the team put each horse through two different tests during the second week of each