Corn (Zea mays L.) silage (CS) is a nutritious food that can be used as a supplement in dairy cows. The aim of this study was to determine the effect of supplementation with two amounts of CS on milk production and composition, live weight and body condition, as well as on some blood indicators for energy and protein metabolism on dairy cows in early lactation and grazing low mass pasture during autumn. The study was carried out in 40 Holstein Friesian cows over 57 d. Prior to experimental treatment, milk production and days of lactation averaged 24.1 ± 2.8 kg d-1 and 62 ± 14 d, respectively. The dietary treatments consisted of two levels of supplementation with CS; 4.5 and 9 kg DM cow-1 d-1 (treatments LCS and HCS, respectively). Additionally, all the cows received a pasture allowance of 21 and 3 kg DM cow-1 d-1 of concentrate. Milk composition was determined using infrared spectrophotometry, while blood indicators were obtained using an autoanalyzer. There were not differences between treatments regarding milk production or composition, total DM or energy intake. Herbage and protein intake was higher for LCS treatment (P < 0.001). Increasing supplementation decreased (P < 0.001) daily weight gain but did not affect body condition. Plasma concentrations of &#946;OH-butyrate were lower (P = 0.038) for the LCS treatment; while urea concentrations were higher (P = 0.003), with no differences for non-esterified fatty acids (NEFA) concentrations. Supplementation with 4.5 kg d-1 of CS was sufficient to meet the production requirements of the cows.