LAUSR

Fermentation in the equine hindgut is key to ensure the assimilation of dietary components such as vitamins, amino acids, and minerals. Furthermore, microbial fermentation products (of volatile fatty acids) provide horses with energy. Imbalances in the gut microbiota could impact the rate of fermentation leading to physiological responses such as hindgut inflammation, over production of lactic acid and ulceration. Feed supplementation with direct fed microbials (DFMs) is a common approach to restore microbial balance and ensure animal health. DFMs transit the gastrointestinal tract through highly acidic conditions in the stomach could result in a reduction of the initial DFMs concentrations. The use of coating technologies to encapsulate pH sensitive microorganisms is a way to ensure the delivery of high concentrations of DFMs in the hindgut. The aim of this study was to evaluate the survivability of a coated and non-coated concentrated yeast at pH 2, 6.3, and 6.8, to simulate pH conditions and digesta residence times of an equine stomach (1 h), small intestine (5 h) and cecum (17 h), respectively. A total of 2 replicates of Saccharomyces cerevisiae concentrate and a coated protected lyophilized Saccharomyces cerevisiae were added to MRS (selective media) broth and RPMI broth (non-selective media) at pH2; 2 additional replicates of each product were added to each selective and non-selective media at pH 7 (control). Samples were incubated at 38°C for one hour; after incubation samples were washed and media at pH 6.3 was added. Tubes were incubated for 5 h, after incubation media at pH 6.6 was added for a final 17-h incubation. pH was measured and S. cerevisiae counts were plated for enumeration after each incubation period. One-way ANOVA was used to identify statistically significant differences among groups. Counts of the coated S. cerevisiae were between 9.8 and 10.1 log10 cfu/g in selective and 9.6–9.8 log10 cfu/g in non-selective media. These counts were not significantly (P > 0.05) reduced compared with controls in selective (10.3–10.4 log10 cfu/g) and non-selective (9.7–10.3 log10 cfu/g) media. No differences were observed between coated – and non-coated concentrated S. cerevisiae. These results showed that S. cerevisiae used in this study survived the simulated transit times and pH conditions of the equine gastrointestinal tract. Concentrations of S. cerevisiae above 9 log10 cfu/g reached cecum simulated pH conditions, the high concentrations found suggest its potential use as a DFM that could enhance dietary components assimilation in the equine hindgut.