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.
Oxidative stress (OS) causes health complications through the destruction of cellular components as individuals age. Reactive oxygen species are used to measure OS through Trolox equivalent antioxidant capacity (TEAC) and thiobarbituric acid reactive substances (TBARS). Other prebiotics have been used to reduce OS markers in numerous species; however, the effect of short-chain fructooligosaccharides (scFOS) on OS has not been studied in the horse. Ten healthy stock-type horses were blocked by age into 2 groups: mature (MA; n = 5; 7.0 ± 0.87 yr) and senior (SR; n = 5; 22.6 ± 1.1 yr) to analyze effects of scFOS on TEAC and TBARS. Horses were randomly assigned to 1 of 3 diets for 25 d before transition to another diet. Diets were bermudagrass hay offered at 1.5% BW/d hay as-fed, hay with a ration balancer (CON), or hay with a ration balancer and scFOS added at a rate of 2.5 g/kg (PRE). Prior to a total fecal collection for an alternate study, horses were fasted overnight for 8 h with blood samples taken immediately prior to feeding (0), 30, and 60 min postprandial. Oxidative stress markers were analyzed for the 2 ration balancer diets. Statistical analysis was performed with SAS using the MIXED procedure with horse within diet as a random effect with significance of P ≤ 0.05. Trolox equivalent antioxidant capacity was unaffected by diet (P = 0.827) or age (P = 0.347). Time (P = 0.006) was significant for TBARS which increased postprandial regardless of treatment or age. Consistent with other species, higher levels of OS was found in SR compared to MA regardless of time or diet (P = 0.037; 4.491 µM vs. 3.412 µM TBARS, respectively). These results indicate that scFOS do not seem to be effective in reducing OS in SR and MA horses.
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