The objective of this study was to determine the short-term effects of targeted rumen-protected and postruminal amino acid supplementation to dairy cows on protein and amino acids in blood; and production of milk and milk components. Eight prototypes (treatment A to H) were tested in 4 different experiments. In each experiment, 2 prototypes were tested at the same time. Treatments were CON, cows were fed a control diet + ground corn without a Lys source; AJP cows were fed a control diet + a commercially available rumen-protected Lys source; and A-H cows were fed a control diet + a not commercially available rumen-protected Lys source. Treatments AJP and A-H were formulated to provide 112% of the cow’s lysine requirements while cows in CON received 94% of the cow’s lysine requirements. Treatments were delivered twice a day (12-h intervals) via 28 mL of gelatin and administered orally via balling gun. Cows were assigned to 1 of 4 treatments in a replicated 4 × 4 Latin square design with experimental periods 7 d in length. Total length of the experiment for 2 prototypes was 28 d. Periods (7 d) were divided in washout phase (d 1, no treatment was delivered), adaptation phase (d 2 to 4), in which treatments were delivered in gelatin capsules, and phase for statistical inferences (d 5 to 7) in which treatments were also delivered in gelatin capsules. Data were analyzed using the MIXED procedure of SAS. Contrast 1 (CONT1): CON compared with AJP, contrast 2 (CONT2): AJP compared with A (C, E, and G in each round respectively); and contrast 3 (CONT3): AJP compared with B (D, F, and H in each round respectively). Four blood samples were collected at 2-h intervals following the morning treatment delivery from each cow on the last 3 d of the covariate period and the last 3 d of each experimental period. Overall, there were a tendency for cows in AJP to have higher plasma lysine concentrations than cows in CON (93.56 and 85.86 ± 3.42 μmol/L, respectively, 0.05 < P ≤ 0.11, CONT1). There were no treatment differences for either contrasts (CONT2 or CONT3) for plasma lysine concentrations (93.56, 86.77, and 90.12 ± 3.42, respectively, P > 0.10).In conclusion, cows in A-H showed similar plasma lysine concentrations than cows in AJP.