Influence of Dietary Starch Inclusion on Cecal Environment and Microbial Populations in Horses

Previous research has documented shifts in microbial hindgut populations resulting from dietary starch inclusion, and recent evidence indicates only 30% of equine cecal contents has been cultured successfully. Next generation sequencing (NGS) techniques allows detection of new species previously undetected. Therefore, the objective of this study was to determine community profiles equine cecal microbiota in response to abrupt dietary starch inclusion. Seven cecally cannulated Quarter horse geldings (497 to 580 kg) were utilized in a crossover design with two 28 d periods and a 28 d washout between each. Horses were randomly assigned to dietary treatments consisting of commercial concentrate offered individually at either 0.6% (LS) or 1.2% BW (HS; as fed) daily divided into 2 meals at 12 h intervals. Prior to start of each period horses were allowed ad libitum access to coastal bermudagrass (Cynodon dactylon) hay and concentrate was fed on d 1 with no adaptation. Samples of cecal fluid were collected on d 1 prior to 0 h and 3, 6, 9, and 12 h post morning meal and on d 1, 2, 3, and 7 at 6 h post morning meal. Cecal pH was determined immediately and a samples of cecal fluid were stored. Genomic DNA was extracted and the V4-V6 segment of 16s rRNA gene was PCR amplified using universal Eubacterial primers 530Fand 1100R and sequenced on the Roche 454 FLX platform. The reads were denoised, chimera checked, and Operational Taxonomic Units (OTUs) were identified using the reference Ribosomal Database Project 16S rRNA dataset. Data were analyzed using PROC MIXED procedure of SAS. Bacterial phyla were largely unaffected by dietary treatment for the first 12 h after the initial concentrate meal except for Verrucomicrobia which was greater in LS horses (P ? 0.04). Regardless of treatment, Bacteriodetes increased (P ? 0.02) over the first 12 h following initial addition of dietary starch. Adaptation to dietary treatments over 7 d resulted in decreased numbers of Tenericutes (P ? 0.07) in HS horses compared to LS. Cecal environment and microbial populations were altered after abrupt and long term exposure to dietary starch.