Rapid Starch Increases, Decreases in Horse Diets Upset Gut Microbiome
Rapidly adding concentrates to horses’ diets resulted in immediate and short-term effects on the cecal microbiome, pH, and VFA production. | Photo: Anne M. Eberhardt/The Horse
It’s one of the golden rules of horse feeding: Make all grain and concentrate changes gradually. Veterinarians have long known the equine digestive system can be sensitive to dietary changes and prone to upset, but, to date, there’s still little research in live horses focusing on how dietary changes can affect the hindgut’s microbial community.

So, a group of researchers at Texas A&M University, in College Station, led by Christine Warzecha, MS, set out to discover how short-term starch inclusion in the diet—essentially, a rapid increase and then decrease in the amount of starch a horse consumes—affects the equine cecal microbiome.

The team fed seven cecally cannulated Quarter Horse geldings (meaning they had tubes permanently placed through their sides and into the cecum so the researchers could collect intestinal contents) a treatment diet for two 28-day periods with a 28-day washout in between. The diets consisted of a commercial concentrate with 30% nonstructural carbohydrates fed at 0.6% body weight (the low-starch diet) or 1.2% body weight (the high-starch diet), along with free-choice coastal bermudagrass hay.

On the first day of each test period, the researchers collected cecal samples prior to the morning meal and again at three-hour intervals for 12 hours to observe the diet’s immediate effects. On Days 2, 3, and 7, they gathered cecal samples six hours after the morning meal. The team analyzed the samples’ pH levels immediately and then froze them for later volatile fatty acid (VFA) content analysis and microbial DNA extraction

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