0821 Effects of Meal Size and Frequency on the Equine Cecal Microbiota

The effects of meal size and frequency on the equine cecal microbiota are not well documented. We hypothesized that meal size will alter the profile of the microbiota present in the equine cecum. Southern Illinois University Institutional Animal Care and Use approval (#13–070) was obtained before the initiation of this research. Cecally cannulated horses (n = 6) with a BCS of 5 (± 0.5) were utilized in this replicated Latin Square (3 × 3) design. All horses received group pasture turnout daily for approximately 6 h and were stalled overnight in identical box stalls (3 × 4 m). Treatment diets of Strategy® pelleted grain-based concentrate were as follows: A = one meal, 2.72 kg, 0600 h; B = two meals, 1.36 kg, 0600 and 1600 h; C = three meals, 0.91 kg, 0600, 1200, and 1600 h. Each treatment period consisted of 8 d of acclimation followed by 3 d of collection. All horses received ad libitum access to water, a white salt block, and 3 kg of mixed alfalfa/grass hay offered overnight. Body weight was recorded weekly and data were analyzed using a Latin square design with the proc MIXED procedure of SAS and was not affected by treatment (P > 0.05) Cecal samples (216 total) were collected four times daily over a three-day collection within each period. Cecal bacterial DNA was extracted, and 16S rRNA amplicon sequencing using Illumina technology was followed by analysis using QIIME 1.8.0 and proc MIXED. Significance was set at (P ≤ 0.05). Weighted principal coordinates analysis (PCoA) of UniFrac distances between samples based on their 97% OTU composition indicated that Treatment A was different than Treatment C (P = 0.028). In addition, PCoA also revealed a significant difference associated with breed (P < 0.05) for both weighted (abundance) and unweighted (community composition) measures. Alpha diversity measures indicated that bacterial diversity is higher in geldings as compared to mares (P < 0.01). Predominant bacterial phyla included Firmicutes (58.8–63.2%); Bacteroidetes (28.78–34.2%); Proteobacteria (2.2–2.8%); and Spirochaetes (2.5–2.7%) for all treatments. Furthermore, when treatment effects were examined at the genus level, six different genera were significantly affected by treatment (Prevotella, YRC22, Lactobacillus, Streptococcus, Coprococcus, and Phascolarctobacterium). These data demonstrate that size and frequency of pelleted concentrate meals affect both the abundance and the composition of the bacteria present in the equine cecum.