One hundred and fifty six Israeli-Holstein cows were randomly allotted to two groups in a continuous design; of these, 59 cows entered the trial within 14 days postpartum. The trial lasted 75 days. Diet 1 (control group) contained 16.5% crude protein (CP), of which 11.0% was rumen-degradable (RDCP). Diet 2 (high-protein; HP) contained 17.8% CP; all the additional protein was planned to be rumen-undegradable. Cows were group-fed. Feed intake and milk yield were recorded daily and milk composition was analyzed every 2 weeks. Dry matter intake, milk, milk fat and protein yields (kg/d) of the control and HP treatments were 21.2 and 20.7 (P ≤ 0.05), 34.3 and 35.5 (P ≤ 0.05), 0.866 and 0.935 (P ≤ 0.05), and 0.963 and 1.002 (P ≤ 0.05), respectively. Average milk, milk fat and protein yields in the control and HP cows that entered the trial within 0-21 d after calving, were 37.0 and 39.6 (P ≤ 0.05), 0.992 and 1.043, and 0.985 and 1.056 (P ≤ 0.05) kg/d, respectively. Supplementation of additional undegradable CP at the beginning of lactation, tended to improve reproductive performance, which was attributed to the earlier recovery of body condition score of those cows.