Date of Award


Degree Name

Master of Science


Animal Science

First Advisor

Venable, Erin


The equine cecal microbiome is an incredibly diverse ecosystem that is critical to the overall health of the horse. It is of particular interest to equine researchers because of the link between colic and the bacterial profile residing within the cecum. We investigated ten probiotics for their ability to reduce numbers of previously identified pathogenic microorganisms: Streptococcus bovis/equinus complex (SBEC), Escherichia coli K-12, Escherichia coli general, Clostridium difficile, and Clostridium perfringens. A preliminary in vitro study was used to measure the reduction in opportunistic bacteria that are commonly found in the equine gastrointestinal tract. The second in vitro was designed as a titration study using the three most effective probiotics from the first project. In this second stage of testing, different dosage levels were utilized to determine if dosage had an effect on bacterial reduction potential. Dosage levels included manufacturer’s recommended dosage (1x), twice the recommended dosage (2x), and three times the recommended dosage (3x). Lastly, an in vivo study was conducted using three cecally-cannulated horses in a Latin square design in order to measure opportunistic bacteria reduction potential in the live horse model. Cecal fluid characteristics, pH, volatile fatty acids, and ammonia concentrations were measured, along with bacterial concentrations. In the initial in vitro experiment, we observed that all probiotic treatments numerically decreased the bacterial concentrations in comparison to the control. There were three products that decreased bacterial concentrations most consistently: Command FT, CRS, and SmartDigest Ultra. These probiotics were chosen for a titration in vitro study. Selected probiotics were dosed at the recommended dose (1x), as well as at two times the recommended dose (2x) and three times the recommended dose. In the titration in vitro experiment, SmartDigest Ultra increased (P < 0.01) bacterial concentrations of E. coli K12 and C. perfringens at 2x and 3x. Due to a lack of statistical significance for Command FT and CRS (P ≥ 0.10), cost efficiency was used as a selection criteria. Command FT was approximately $0.27 per dose and CRS was approximately $0.18 per dose. Therefore, CRS was chosen for further testing in the following in vivo experiment. In the in vivo experiment, CRS was dosed at one times (1x) and two times (2x) the recommended dose. We observed that blood parameters, cecal fluid characteristics, and bacterial concentrations were not statistically (P ≥ 0.10) altered by treatment. Numerical increases for bacterial concentrations were observed for SBEC at 1x and 2x, C. difficile at 2x, and C. perfringens at 2x. Numerical decreases were observed for E. coli K12 at 1x and 2x and E. coli general at 1x and 2x. Overall, this study suggests that the selected probiotics can be safely used at the recommended dose.




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