The undesirable effects of high-starch diets on the equine gut microbiota

Abstract

High-starch diets are considered a detrimental factor to the homeostatic balance of the equine gut microbiota. The gut microbiota of horses is a complex and dynamic community of microorganisms that interacts closely with the gut environment to regulate digestive health, which in turn impacts the immune system and the horse’s overall well-being. Even slight changes in the type or amount of dietary carbohydrates can significantly alter the composition of microbial populations in the digestive tract, thereby affecting gut function. Horses fed high-starch diets are at increased risk of developing various digestive and systemic disorders, including diarrhea, colic, laminitis, and metabolic diseases. Numerous studies have investigated the proliferation of certain microbial groups—particularly lactic acid-producing bacteria such as Lactobacillus, Streptococcus, and Enterococcus—in response to high starch and fructan intake. Using advanced techniques such as DNA sequencing, researchers have also examined how the abundance of these groups can disrupt the microbial balance, notably through the reduction of fibrolytic bacteria, which are essential for fiber digestion and are typically more abundant in high-fiber diets. While good management practices and a well-balanced diet remain the cornerstone strategies recommended by veterinarians to prevent gut microbiota dysbiosis, recent interest has grown in supplementary approaches such as prebiotics, probiotics, and postbiotics to modulate gut health. However, the efficacy of these interventions remains under investigation, and they are currently considered complementary or holistic approaches rather than definitive solutions.