Třináctý J. author Křížová L. author Richter M. author Černý V. author Říha J. author text journal article 2009 The objective of this study was to determine the effect of supplemental lysine (Lys), methionine (Met) or both amino acids added in the form of rumen-protected (RP) tablets with copolymer coating to a diet of dairy cows on yield and composition of milk and concentration of plasma amino acids (AA). The experiment was carried out on four high-yielding lactating Holstein cows with average milk production of 33.5 kg/day in the form of Latin square design. The four treatments were as follows: C - control without AA supplementation, L - control plus supplement of RP Lys, M - control plus supplement of RP Met and ML - control plus supplement of RP Met and Lys. The experiment was divided into 4 periods. Each period (14 days) consisted of 10-day preliminary period and 4-day experimental period. Cows were fed a diet based on maize silage, lucerne hay and supplemental mixture. Average milk yield recorded in ML was 34.18 kg and was higher than that recorded in L or M (32.46 kg and 32.13 kg, respectively P < 0.05) and tended to be higher than in C (33.33 kg, P > 0.05). The content of protein and casein was higher in L and ML in comparison with C (P < 0.05) and tended to be higher than in M (P > 0.05). Protein yield in ML (1 054 g/day) was higher than that found in C, L or M (990, 998 or 968 g/day, respectively, P < 0.05). The same response was found for casein yield (P < 0.05). Although the proportion of individual casein fractions was not affected by the treatment, the yield of α- and β-casein differed (P < 0.05) while the yield of κ-casein was not affected by the treatment. Concentrations of blood metabolites, except for betahydroxybutyrate (BHB), were not changed. Plasma Met concentrations were increased (P < 0.05) in the M and ML group. Similar, but insignificant increases (P > 0.05) were also observed in plasma Lys in the L and ML group. amino acids; rumen protection; dairy cow; lactation performance; plasma amino acids 10.17221/1730-CJAS https://cjas.agriculturejournals.cz/artkey/cjs-200906-0001.php https://cjas.agriculturejournals.cz/artkey/cjs-200906-0001.php continuing 54 6 239 248 2009 12121819 periodical academic journal