PSII-18 Awardee Poster: Direct fed microbial supplementation on apparent nutrient digestibility, visualization of the top three fecal microbial isolates, and blood metabolites in the moderately exercised horse

Abstract

Abstract Performance horses subjected to intensive training and competition are exposed to elevated physiological stress. Decreased blood cortisol has been reported with direct fed microbial (DFM) supplementation. Eight stock-type horses (8.13 ± 1.31 yr; 489.77 ± 19 kg) were used in a completely randomized design to determine the effect of DFM on the apparent digestibility of nutrients, fecal microbial profile, and blood metabolites in moderately exercised horses. Diets were 1.5% BW/d of a 50/50 bermudagrass and alfalfa hay with 0.5% BW/d of control (CON) grain or grain with DFM. The DFM contained Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium thermophilum, Enterococcus faecium, and Saccharomyces cervisiae at a rate of 25.1 x 109 cfu/g of grain, averaging 61.5 x 1012 cfu/d. After a 21-d washout period, horses were transitioned to 1 of 2 diets for a 21-d treatment. Horses were moderately exercised 3 d/wk for 1 h. Blood was collected pre-and post-exercise and fresh per rectum fecal samples were collected to determine the top 3 microbial isolates. A total fecal collection was performed the last 72 h of the treatment. Statistical analysis was performed using the MIXED procedure of SAS with horse within diet as a random block effect and as a subject of repeated measures. There were tendencies for increases in apparent ADF digestibility (P = 0.064) and mean HR (P = 0.075) for DFM. Resting lactate was decreased (P = 0.036) with DFM and post exercise cortisol was not affected (P = 0.944). Of the top 3 isolates identified, Escherichia coli (EC) and Streptococcus equi subsp. zooepidemicus accounted for 90% of isolated bacteria. A heat map was created to assess fecal bacteria shifts, which found clustering dependent on sex, with mares excreting more EC than geldings. Results indicate DFM may have an impact on nutrient digestibility and microbial populations in exercise-stressed horses.