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 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 (7d) 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. Three treatment orthogonal contrasts were used. 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). There were no treatment differences for either contrasts (CONT1 or CONT2) for DMI, BW, or BCS (P > 0.10). Milk protein yield was higher for cows in B (1.21 ± 0.1 kg/d) than AJP (1.14 ± 0.06 kg/d, P = 0.02; CONT3).Cows in B (16.15 ± 0.5mg/dL) had lower MUN concentration compared with cows in AJP (17.2 ± 0.6mg/dL, P = 0.05, CONT3). However, there were no treatment differences for either CONT2 or CONT3, and MUN concentrations were lower for cows in both C and D than AJP (P > 0.10). In conclusion, cows in B performed similarly than cows in AJP and seem to have lower protein breakdown than cows in AJP.