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RICHTER, M., TŘINACTÝ, J., KŘIŽOVA, L.: Comparison of actual and predicted amino acid contents in the duodenal digesta of dairy cows. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 5, pp. 313–320 In this experiment on three dairy cows with the ruminal and duodenal T-cannulas, the actual and predicted amino acid (AA) profi les of the protein fraction fl owed to the small intestine were compared. The prediction was calculated by two methods: with the use of mean published AA profi le of microbial protein and of experimentally determined one. The actual AA profi le of digesta protein was corrected for glycine (Gly) of bile origin. In comparison to the published AA profi le of microbial protein the use of the actual one did not contribute to an improvement of prediction accuracy (mean prediction error: 7.36 vs. 7.54 %, respectively). Inaccurate determination of AA composition of undegraded feed protein and the insuffi cient correction for Gly of bile origin were the probable sources of the residual variability. amino acids, dairy cow, duodenum, microbial protein, prediction As regards the requirement of crude protein, the diets for cattle are evaluated in the French PDI system (Jarrige, 1990) on the basis of prediction of the fl ow of protein truly digestible in the small intestine (PDI). This protein consists of two basic fractions: rumen undegraded feed protein (PDIA) and microbial protein (PDIM), the amount of which correlates with the fermentable part of feed. The equation to calculate the second fraction is depending upon whether the limiting factor of its formation is energy (PDIME: microbial protein digested in the intestine when rumen fermentable energy is limiting) or crude protein (PDIMN: microbial protein digested in the intestine when rumen fermentable nitrogen is limiting). The resulting predicted value of true digestible protein (PDIE, PDIN) is the sum of these two basic fractions provided by diff erent components of the diet (Jarrige, 1989). Even with a correct prediction of these values and subsequent balancing of PDI requirement, with some diets it is impossible to achieve maximum production of milk or meat. This is due to defi ciencies of some amino acids (AA), which was confi rmed e.g. by the duodenal infusion of Lys and Met in lactating cows fed on maize silage based diet (Schwab et al., 1992), or of His in cows fed grass silages (Vanhatalo et al., 1999). For this reason, a need to defi ne the diet occurred, not only in terms of the fl ow of basic protein fraction, but also in terms of representation of individual especially essential AA in PDI. For this purpose, on the basis of the existing French PDI system, a consequential AADI system was proposed (Rulquin et al., 1993; Rulquin & Verite, 1993). The fi nal value of AADI (% PDIE) of a given AA results from its content in the undegraded residue of feed protein and microbial mass protein formed in the rumen with contribution of the degraded feed components. Because PDI is constituted of more than 50 % of microbial protein (Rulquin et al., 1998) and because of large diff erences in AA profi le of bacteria protein (Clark et al., 1992; Rulquin & Verite, 1993), the main source of variability of predicted AADI values is microbial mass. The aim of this study was to compare the experimental and predicted AA profi les of the digesta entering the small intestine using the method described by Rulquin et al. (1998) and compare the accuracy of prediction when using the pub314 M. Richter, J. Třinactý, L. Křižova lished mean (Le Henaff , 1991) and actual AA profi les of microbial protein in lactating dairy cows. MATERIAL AND METHODS Experiment, animals, feed For the evaluation of actual and predicted amino acid content in the duodenal digesta, the data from previous studies (Třinactý et al., 2006, Křižova et al., 2007) were used. Cows, treatments and feeding regiment have been described previously (Třinactý et al., 2006). Briefl y, treatment consisted of administrations of either rumen-protected tablets (T) or powder (C) containing purifi ed soya-protein HP 300 (Hamlet Protein A/S, Denmark) and amino acids Lys, Met and His into the rumen of three lactating Holstein cows (1–3 lactation, 17–35 week of lactation) of mean live weight 523 kg (SEM = 17) and milk yield 16.7 kg . day−1 (SEM = 0.38). Cows were fi tted with ruminal and duodenal T-cannulas (Komarek, 1981). The experiment was divided into 4 periods. Each period (14 d) consisted of 10–d preliminary period and 4–d experimental period. Cows were fed individually twice daily (7.00 and 16.35 h) ad libitum a diet based on maize silage (54.7 %), lucerne hay (15.0 %) and concentrate (30.3 %). The experimental protein supplement consisted of ground soya protein HP 300 (93 %), Lys (1.6 %), Met (2.4 %) and His (3.0 %) and was prepared in two forms, either as rumen-protected tablets or powder. Tablets or powder together with chromic oxide (digesta passage marker) were wrapped into fi lter paper and inserted into the bottom of the rumen via ruminal cannula twice daily before feeding. Daily amount of these ingredients were as follows (g): HP 300 (306), Lys (5.7), Met (8.8), His (10.6) and chromic oxide (15.0). In the previous study focused on the estimation of duodenal fl ow of soluble nitrogen fractions in the same experiment (Křižova et al., 2007), it has been found that in the case of ruminally protected tablets sampling from the duodenal cannula was unrepresentative. Thus for the evaluation of actual and predicted amino acid content in the duodenal digesta only the data from the control group of animals (C) receiving the supplement in the powder form were used. Collection, processing and analyses of samples Feed samples were collected on the third day of each experimental period. Respective orts from each cow were collected and weighed during the four-day experimental period before each meal and stored in a freezer. A er the experimental period, the orts were pooled for each cow, homogenized and the representative sample was taken. The rumen fl uid samples (1 l) were collected from each cow once a day, during the four-day experimental period with a 2h time shi between the successive days (at 9.00, 11.00, 13.00 and 15.00 h). To the 500 ml of rumen fl uid sample the same volume of 0.95 % NaCl solution were added. The mixture was stirred in the blender and fi ltered through 4 layers of tissue, and then stored at –20 °C (Cecava et al., 1990). A er thawing the samples were processed according to Schwab et al. (1992). The samples of microbial mass were pooled for each cow and experimental period, freeze-dried and homogenized. The samples of duodenal digesta (500 ml) were collected during the 4-day experimental period at 6 h intervals from each cow and immediately frozen to –20 °C (Schwab et al., 1992). Processing of feed, feed refusals and duodenal chymus samples for analyses has been described in details elsewhere (Křižova et al., 2007). In feed and feed refusals samples the following parameters were estimated according to AOAC (1984): dry matter (DM), ash, crude protein (CP), fat (F) and crude fi bre (CF). Neutral detergent fi bre (NDF) with -amylase and acid detergent fi bre (ADF) were estimated according to Van Soest et al. (1991). Content of Cr in samples of duodenal chymus were estimated according to Williams et al. (1962). Ammonia nitrogen content in duodenal chymus was estimated in a water eluate (2 g.100ml−1 of distilled water) using a gas electrode (manufacturer Radelkis Ltd., Hungary). DM, ash and CP contents in the microbial mass and digesta were determined using the same procedure as in feeds. In samples of feeds, microbial mass and duodenal chymus content of individual AA was determined. Samples were adjusted using acidic and oxidative acidic hydrolysis. The chromatographic analysis of sample hydrolysates was performed in the analyser AAA 400 (INGOS Prague, CR) and using Na-citrate buff ers and ninhydrin detection.