Starch Overload and Cecal Alkalinization: Impacts on the Intestinal Microbiota and Health of Horses

Starch overload induces dysbiosis primarily through a reduction in cecal pH. This study aimed to evaluate the cecal microbiota following excessive starch intake, with or without the administration of an intracecal buffering solution. We hypothesized that the buffering solution would mitigate changes in the intestinal microbiota and associated clinical signs. Ten horses were randomly assigned to two groups, each receiving distinct treatments (Group I: saline solution [WSa] and starch-buffer [SB]; Group II: buffer-water [WB] and starch-saline [SSa]). Following starch overload (17.6 g/kg body weight via nasogastric tube), clinical assessments and cecal content sampling were conducted at six time points (T0, T08, T12, T24, T48, T72), corresponding to 0, 8-, 12-, 24-, 48-, and 72-hours period. DNA was extracted, and the V4 region of the 16S rRNA gene was amplified and sequenced using the Illumina platform. Sequence data were processed using QIIME2. Statistical analysis was performed using the ExpDes package in R, with means compared via Tukey's test. Diversity analysis revealed decreased richness and evenness post-treatment in Group I, with reductions observed as early as T08 in the SB treatment. The relative abundance of <i>Bacillota</i> significantly increased in the SB and SSa treatments between T08 and T24, whereas <i>Bacteroidota</i> showed a concurrent decline. All horses receiving these treatments exhibited at least one clinical sign following starch overload, with the SB treatment associated with more severe and prolonged clinical manifestations. The administration of the buffering solution in combination with starch overload exacerbated alterations in the intestinal microbiota and clinical outcomes.