Plasma biomarkers of feed efficiency differ across two contrasting diets in growing beef cattle

International audience

English. Beef cattle industry could benefit from the identification of individuals with superior feed efficiency. Thus, biomarkersshould be developed and validated to contribute to this objective. This study aimed to explore plasma biomarkersof residual feed intake (RFI) in fattening beef cattle through a targeted metabolomics approach. For this, 167 youngCharolais bulls were tested for RFI in 3 independent cohorts during at least 6 months. Animals within each cohortwere evenly assigned to either a high-starch corn silage diet or a high-fibre grass silage diet. Blood was sampled fromeach animal one month before the end of the test. Plasma from the 48 most extreme animals in terms of RFI (24 lowvs 24 high RFI; balanced within cohorts and diets) were analysed for 630 metabolites by FIA- or LC- tandem massspectrometry. Metabolites were analysed by ANOVA separately for each diet including the fixed effect of cohort, RFIgroup and their interaction. In the corn silage diet, plasma concentration of the 3 branched-chain amino acids (BCAA;Leu, Ile and Val) was lower (-15%; P≤0.01) in low-compared to high-RFI, likely reflecting their higher metabolicuse for protein synthesis and muscle accretion. In contrast, creatinine and hydroxyl-proline, markers of muscle andcollagen body mass respectively, showed higher plasma concentration (+18-20%; P≤0.01) in low- compared tohigh-RFI animals. In the grass silage diet, most of the RFI discriminant metabolites belonged to different classes oftriglycerides and their plasma concentrations were always higher (+50% on average; P=0.003) in low- comparedto high RFI animals, indicating either their lower incorporation into fat cells or their lower use as energy substrateby the muscle. Only creatinine was a common RFI discriminant metabolite in the two diets and Val, though alsodiscriminant, showed opposite trends. Our results suggest that discriminant metabolites of RFI are not the same acrosstwo contrasting diets. However, differences in muscle body mass revealed by plasma creatinine concentration seemsto be a determinant of RFI regardless the diet.