Milk performance of four groups of cows (H0, H4, N0 and N4) was studied under grazing: two cow breeds, Holstein-Friesian (H) vs. Normande (N), supplemented at pasture with two levels of concentrate, low vs. high (0 and 4 kg cow–1 day–1). A simplified rotational grazing system using three paddocks per rotation with a mean residence time per paddock of 10-days was examined. During this long residence time, maximum milk yield (MY max.) was reached at day 4 followed by a milk yield drop (Dm) at the end. Milk production was higher (P < 0.001) in Holstein-Friesian than in Normande cows (7,452 over 6,067 kg cow–1 year–1). Supplemented cows produced more (P < 0.001) milk than unsupplemented cows (7,570 over 5,949 kg cow–1 year–1). In each 10-day grazing cycle, supplemented cows had higher (P < 0.001) peak (MY max., 25.6 kg cow–1) and less (P < 0.001) drop (Dm – 5.3 kg cow–1) than those without concentrate (21.2 and – 5.7 kg cow–1). The peaks and drops of milk yield were higher (P < 0.001) in Holstein-Friesian (25.5 and – 6.2 kg cow–1) than in Normande cows (21.3 and – 4.7 kg cow–1). When long-residence grazing paddocks are used, these peaks and drops of milk yield are important factors to control for a good milk performance considering both the cow breeds and the supplementation effects.