Dietary fats are important components of performance horses' diets because they are calorie-dense and energy-rich. Previous studies have shown, however, that diets high in soybean oil interfere with fiber digestion in trotters. It is unclear whether feeding poorly digestible carbohydrates, like cornstarch, compounds this problem by overloading the cecum and altering its bacterial population.

Researchers at the Utrecht University in The Netherlands recently conducted a study to determine whether the inhibitory effect of soybean oil on fiber digestion is influenced by concurrent feeding of cornstarch.

Six trotters were fed three diets in three-week rotations. Each diet had one main source of energy--soybean oil, cornstarch, or glucose. The glucose diet served as a control measure, because glucose is almost completely digested in the small intestine, rarely entering the cecum or colon.

The results of the study suggest that the negative effect of soybean oil on fiber digestion in trotters is a specific effect, not influenced by cornstarch in the diet. This conclusion was drawn because the cornstarch and glucose diets produced the same effects on fiber digestion. It is unlikely, then, that cornstarch adversely effects fiber digestion.

What is still uncertain is how high-fat diets decrease fiber digestion. Previous studies have suggested that increased fat inhibits the activity of resident microbes in the cecum and colon. However, evidence of this action is lacking. Further studies are needed to clarify this unusual dose-effect relationship between fat and fiber in the horse.

Jansen, W.L.; Geelen, S.N.J.; van der Kuilen, J.; et al. Equine Veterinary Journal, 34 (3), 302-305, 2002.