Fecal metabolites associated with feed efficiency and methane emission in Nellore cattle

Abstract

Metabolomics can offer a powerful approach to elucidate the biological mechanisms underlying feed efficiency and methane emission. This study aimed to identify metabolites associated with feed efficiency and methane emission phenotypes in Nellore cattle. A total of 175 Nellore cattle aged 418 ± 87 days from three selection lines - NeC (stabilizer selection), NeS (selected for post-weaning weight) and NeT (selected for post-weaning weight and residual feed intake) - were housed in group pens equipped with electronic troughs for automated recording of individual daily feed intake. Methane (CH4) emissions were measured using the SF6 tracer technique. Fecal samples were collected and metabolites analyzed by 1H NMR spectroscopy. The phenotypes of average daily gain (ADG), average daily residual gain (RADG), body weight (BW), metabolic body weight (MBW), dry matter intake (DMI), feed conversion rate (FCR), feed efficiency (FE), CH4 by DMI, ADG, and MBW were measured. Associations between metabolites and phenotypes were evaluated using linear models, which included the fixed effect of selection line and the phenotype of each animal as a covariate. Association was considered significant when p ≤ 0.05. 3-phenylpropionate, acetate and glucose exhibited negative associations with FE. Furthermore, acetate showed a strong negative association with FE. Acetamide, acetate and isopropanol were positively associated with BW, DMI and MBW. These same traits were negatively associated with 4-hydroxyphenyllactate. Acetamide also showed a negative association with CH₄/MBW. Glucose was positively associated with DMI, FCR, CH₄/AGD, and CH₄/DMI. However, it was negatively associated with RADG and FE. Histidine, isopropanol, and pyruvate were positively associated with MBW. Among them, only isopropanol showed a positive association with CH₄/DMI, while pyruvate showed a significant positive association with CH₄/ADG. These findings highlight distinct fecal metabolite profiles associated with feed efficiency and methane emission, presenting potential biomarkers for improving sustainability in beef cattle production systems.