title: Exogenous lactobacilli mitigate microbial changes associated with grain fermentation (corn, oats, and wheat) by equine fecal microflora ex vivo.
abstract: Cereal grains are often included in equine diets. When starch intake exceeds foregut digestion starch will reach the hindgut, impacting microbial ecology. Probiotics (e.g., lactobacilli) are reported to mitigate GI dysbioses in other species. This study was conducted to determine the effect of exogenous lactobacilli on pH and the growth of amylolytic and lactate-utilizing bacteria. Feces were collected from 3 mature geldings fed grass hay with access to pasture. Fecal microbes were harvested by differential centrifugation, washed, and re-suspended in anaerobic media containing ground corn, wheat, or oats at 1.6% (w/v) starch and one of five treatments: Control (substrate only), L. acidophilus, L. buchneri, L. reuteri, or an equal mixture of all three (107 cells/mL, final concentration). After 24 h of incubation (37°C, 160 rpm), samples were collected for pH and enumerations of total amylolytics, Group D Gram-positive cocci (GPC; Enterococci, Streptococci), lactobacilli, and lactate-utilizing bacteria. Enumeration data were log transformed prior to ANOVA (SAS, v. 9.3). Lactobacilli inhibited pH decline in corn and wheat fermentations (P < 0.0001). Specifically, addition of either L. reuteri or L. acidophilus was most effective at mitigating pH decline with both corn and wheat fermentation, in which the greatest acidification occurred (P < 0.05). Exogenous lactobacilli decreased amylolytics, while increasing lactate-utilizers in corn and wheat fermentations (P < 0.0001). In oat fermentations, L. acidophilus and L. reuteri inhibited pH decline and increased lactate-utilizers while decreasing amylolytics (P < 0.0001). For all substrates, L. reuteri additions (regardless of viability) had the lowest number of GPC and the highest number of lactobacilli and lactate-utilizers (P < 0.05). There were no additive effects when lactobacilli were mixed. Exogenous lactobacilli decreased the initial (first 8 h) rate of starch catalysis when wheat was the substrate, but did not decrease total (24 h) starch utilization in any case. These results indicate that exogenous lactobacilli can impact the microbial community and pH of cereal grain fermentations by equine fecal microflora ex vivo. Additionally, dead (autoclaved) exogenous lactobacilli had similar effects as live lactobacilli on fermentation. This latter result indicates that the mechanism by which lactobacilli impact other amylolytic bacteria is not simple resource competition.
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington KY, United States of America.
authors.forename: Brittany E
authors.initials: BE
authors.lastname: Harlow
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington KY, United States of America.
authors.forename: Laurie M
authors.initials: LM
authors.lastname: Lawrence
authors.affiliation: Equine Studies Group, WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire, United Kingdom.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Harris
authors.affiliation: Forage Animal Production Research Unit, Agricultural Research Service, United States Department of Agriculture, Lexington KY, United States of America.
authors.forename: Glen E
authors.initials: GE
authors.lastname: Aiken
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington KY, United States of America.|Forage Animal Production Research Unit, Agricultural Research Service, United States Department of Agriculture, Lexington KY, United States of America.
authors.forename: Michael D
authors.identifier: http://orcid.org/0000-0002-8868-9169
authors.initials: MD
authors.lastname: Flythe
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D018554:Avena / Q000737:chemistry; D004063:Digestion / Q000502:physiology; D005243:Feces / Q000737:chemistry / Q000382:microbiology*; D005285:Fermentation / Q000187:drug effects; D006095:Gram-Positive Cocci / Q000737:chemistry / Q000378:metabolism*; D006736:Horses / Q000382:microbiology; D006863:Hydrogen-Ion Concentration; D007778:Lactobacillus / Q000737:chemistry / Q000378:metabolism*; D019936:Probiotics / Q000737:chemistry / Q000378:metabolism*; D013213:Starch / Q000737:chemistry / Q000378:metabolism; D014908:Triticum / Q000737:chemistry; D003313:Zea mays / Q000737:chemistry
chemical_list: D013213:Starch