The Fecal Metabolome Differs Between Nelore Bulls Fed Pre- and Post-Feedlot Diets: Initial Results.

The objective of this study was to evaluate the fecal metabolome of Nelore bulls (Bos taurus indicus) fed pre- and post-feedlot diets. In pre-feedlot, 21 animals belonging to the Nelore Qualitas breeding program aged 666 ± 68 days old, and 534.5 ± 34.2 kg of body weight were allocated to one pen for 15 days. The prefeedlot diet contained corn silage (80%) and sugarcane bagasse (20%). Next, the bulls (546.0 ± 41.2 kg of body weight) were submitted into a finishing stage in feedlot for 56 days. During the post-feedlot diet contained wet grain corn (44.6%), corn silage (27.6%), citrus pulp (11.9%), peanut bran (8%), sugarcane bagasse (4.9%), premix (1.8%) and urea (1.2%) twice a day with ad libitum access in Intergado electronic troughs (Intergado Ltda., Contagem, Minas Gerais, Brazil). Pre- and postfeedlot fecal samples were collected directly from the rectal ampulla of each bovine and stored in a -80℃ freezer for metabolomic assays by Nuclear Magnetic Resonance analysis (1H NMR). The metabolites were identified, quantified and data processing using the Chenomx NMR Suite 8.6 (Chenomx Inc., Edmonton, AB, Canada) and MetaboAnalyst 5.0 (http://www. metaboanalyst.ca). We identified and quantified 57 and 55 metabolites in the fecal samples of the bulls fed preand post-feedlot diet, respectively. We observed that 39 metabolites differed (P < 0.05) between pre- and post-feedlot diet. The 2-phenylpropionate, caprylate, fumarate, deaminotyrosine, gamma-glutamyl phenylalanine, NADH, thymidine and pantothenate were observed only in the pre-feedlot diet. However, acetamide, 2-oxoglutarate, uracil, xanthine, trimethylamine and demethyl sulfone were consumed exclusively postfeedlot diet. Our multivariate analyses demonstrated that the fecal metabolite profiles of the Nelore bulls fed pre- and post-feedlot diet were different. The first two components of principal component analysis (PCA) explained 86.1% of the total data variance (PC1 = 77.6%; PC2 = 8.5%). Likewise, the partial least squares discriminant analysis (PLS-DA) explained 85.5% of the data variance with the first two components (component 1 (74.4%) vs. component 2 (8.1%)). Three fecal metabolites (acetate, butyrate, and propionate) with variable importance in the projection (VIP scores over 1.0; P < 0.05) were greater in animals fed post-feedlot diet. Additionally, metabolome profile offers information on the main metabolic pathways, and five pathways were identified as different (P < 0.05 and impact >2) in the fecal samples that bulls fed pre and post feedlot diets: pyruvate metabolism (bta00620); glycine, serine and threonine metabolism (bta00260); synthesis and degradation of ketone bodies (bta00088); histidine metabolism (bta00340) and biosynthesis of phenylalanine, tyrosine and tryptophan (bta00400). Our results suggest that pre- and post-feedlot diets modify the fecal metabolome profile of Nelore bulls. In addition, further studies about metabolic effects of diets are required for a better understanding of these influence on Nelore bulls. [ABSTRACT FROM AUTHOR]