Current requirements of the branched chain amino acids (BCAA) isoleucine (Ile), leucine (Leu), and valine (Val) have been estimated empirically in dose-response experiments using pig growth as the response criteria. The metabolic response to the optimum dietary BCAA levels may be an alternative to animal growth as the response criteria and would use fewer animals in short-term studies. Previous dose-response studies in our laboratory demonstrated that 0.52 standardized ileal digestible (SID) Ile:lysine (Lys), 0.70 SID Val:Lys, and 0.93 SID Leu:Lys are the minimum BCAA requirements to support the best growth performance of weaned piglets (Soumeh et al., 2014, 2015a, b). The objective of the current study was to first, identify biomarkers of BCAA intake status that are linked to animal growth, and second to develop a method to study BCAA requirement in pigs based on blood metabolites in a short term trial using only a few animals. Three dose-response experiments were conducted to study growth performance of pigs (N=96 per study) that were fed with increasing levels of SID Ile:Lys (0.42, 0.46, 0.50, 0.54, 0.58, and 0.62); SID Val:Lys (0.58, 0.62, 0.66, 0.70, 0.74, and 0.78); and SID Leu:Lys (0.70, 0.80, 0.90, 1.00, 1.10, and 1.20). At d 8 and 15 of each experiment, after an overnight fast, pigs were supplied with 25 g/kg metabolic BW of feed and blood and urine samples were collected 3 h later from 8 pigs per treatment. Blood and urine samples were analyzed by a HPLC−MS in a non-targeted metabolomics approach to determine the metabolic profile of pigs fed increasing dietary levels of BCAA:Lys. Principle component analyses (PCA) and partial least squares regression (PLS) were used to identify discriminating metabolites. The identified biomarkers were used as response criteria in the next trial using the diets of previous studies (stored at -20°C) in a 6 × 6 Latin square design (6 BCAA levels × 6 pigs per BCAA level). The experimental diets were fed for 2 days and switched to the next diet after that for a total of 12 days. Blood samples were taken after 2 days and analyzed for biomarkers. Of the several identified discriminating metabolites in each study, few showed significant response to increasing dietary levels of Ile, Leu, and Val in 2-day trials. Fitting different statistical models to these metabolites however, allowed estimation of a minimum requirement for each BCAA that were close to the values determined using traditional growth performance criteria. The results indicate that blood biomarkers have potential as response criteria in short term dose-response studies to estimate BCAA requirement.



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