A total of 24 Friesian cows between the 1^st and 3^rd parity  and  average body weight (LBW) of 512.6 ±15.5 kg were divided into three similar groups (n=8  each) based on their BW, parity and milk production of the previous season. Cows of the 1^st group (G1) were fed concentrate feed mixture (CFM) (control group). Cows of the 2^nd group were received oral dose L-tyrosine 50 g/cow at 21 day (G2) while those of the 3^rd group (G3) were received the same dose of G2 but on day 40. Throughout the experimental period, cows were machine milked and daily milk yield was individually recorded for the 1^st four months. Milk composition and somatic cell count were determined. Estrus was detection and cows in heat were inseminated. Also, number and length of estrous cycles from calving up to conception were recorded. Postpartum 1^st ovulation (PPOI), 1^st estrus (PPEI) and 1^st service (PPSI) intervals, number of services per conception (NSC), days open (DO) and conception rate (CR%) were calculated. Pregnancy was diagnosed by rectal palpation on day 60 post-insemination.  Results revealed that L-tyrosine treatment improved (P<0.05)  daily milk production of G2 and G3 by 15.6 and 16.3% compared to G1. G3 had higher (P<0.05) percentages of fat, protein and lactose as compared to G1 (3.64, 3.07 and 4.16 vs. 3.54, 2.75 and 4.00%), respectively. G2 had  higher  (P<0.05) percentages of protein and lactose (2.98 and 4.28%, respectively) compared to G1, while fat percentage was similar to G1. Treated cows with L-tyrosine showed lower (P<0.05) somatic cell count in milk as compared to G1. Postpartum estrous interval  was  shorter  (P<0.05), by 11.5 days in G2 than G1, While, those of G3 showed longer period (+ 8.13 day)  than G1. Days open in G2 and G3 cows was shorter  (P<0.05) by 21 or 13.2 day, respectively, than  G1. Number of services per conception was less (P<0.05) in G2 (1,63) and G3 (2.0) than in G1 (2.6). conception rate  increased (P<0.05) in G2 and G3 compared with those of control (50 vs. 75 and 100%).