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Traditional AA dose-response studies utilize many animals for evaluation of growth performance, and it is hypothesized that a new experimental design based on modern analytical techniques can reduce the number of used animals. The objective was to evaluate a short-term approach with a low number of pigs based on plasma metabolites as a method to determine the dietary Ile, Leu, and Val requirements. Three separate 6 × 6 Latin square experiments having 6 replicates per treatment were conducted with 6 diets containing increasing concentrations of Ile, Leu, and Val which were fed to 6 pigs (BW 8–9 kg) for 2 days, each without a wash-out period for a period of 12 days. The diets were prepared and used in 3 previous traditional-design dose-response studies and had been stored at −20 °C. Blood samples were collected at the end of each 2-day period, and plasma was analyzed for AA and other metabolites using a metabolomics approach. Out of the 18 analyzed plasma AA, 11, 16, and 3 AA for Ile, Leu, or Val, respectively, showed linear or quadratic responses ( P < 0.05) which could be linked to animal growth. The same was found for 4 non-AA metabolites in the Ile, and for 7 non-AA metabolites in the Leu study. 3-Methyl-2-oxovaleric acid, ketohexanoic acid, and α-ketoisovaleric acid were discriminating metabolites for both Ile and Leu. It was possible to fit least squares means of 5, 14, and 2 metabolites in the Ile, Leu, and Val experiments to curvilinear-plateau, broken-line, or quadratic models and thereby estimate an optimum dietary BCAA level. The average optimum BCAA levels across metabolites and models were 0.54 standardized ileal digestible (SID) Ile:Lys, 1.04 SID Leu:Lys, and 0.68 SID Val:Lys which were close to optimums of 0.52, 0.93, and 0.70 found in the previous dose-response studies based on animal growth performance. In conclusion, certain plasma metabolites could be used to estimate Ile, Leu, and Val requirements, and 2 days of adaptation to a new diet was sufficient to reflect relevant biological changes in the blood to different levels of dietary AA in the current study. [ABSTRACT FROM AUTHOR]

Nutritional feed values are currently based on aggregate criteria such as the ileal or faecal digestibility. Digestibility is the result of several processes including hydrolysis, absorption, secretion and passage. In order to develop mechanistic models of digestion to be used for feed evaluation, these processes have to be quantified. The aim of the current study was to determine the enzymatic hydrolysis (or: in vitro digestion) kinetics of main constituents (organic matter, nitrogen and starch) in wheat, barley, wheat bran and soybean meal, using a three-step, enzymatic in vitro method that mimics digestion in the stomach, small and large intestine of pigs. The in vitro results were compared with in vivo results. Hydrolysis kinetics (i.e., solubilisation of feed constituents) was modelled using an exponential segmented model estimating the extent and rate of digestion for each enzymatic digestion step. In vitro digestion of organic matter of soybean meal occurred mainly through the action of pepsin (0.67 versus <0.30 for other feeds, P<0.05), which was caused by the enzymatic digestion of protein at this site. Organic matter of cereals was mainly hydrolysed by enzymes mimicking digestion in the small intestine, and was mainly caused by starch digestion. Fractional in vitro digestion rates of organic matter were higher in the stomach than in the small intestine for cereals (0.20–0.34 min−1versus 0.02–0.15 min−1, P<0.05). The potential in vitro digestibility of organic matter was nearly 0.88 for wheat and soybean meal, 0.79 for barley and 0.61 for wheat bran, which correspond to typical in vivo digestibility values. The in vitro digestibility corresponded reasonably well to in vivo results for enzyme systems mimicking ileal and total tract digestion. The results of this study indicate that it is possible to quantify dynamic aspects of digestion of feedstuffs fed to non-ruminant animals. [Copyright &y& Elsevier]