The goal of this study was to evaluate the ruminal metabolic parameters and milk fatty acid composition of cows managed under continuous grazing on Marandu grass. Four rumen-cannulated Holstein x Gyr cows with an average milk yield of 21±2 kg day-1 and 79±16 days in milk were used in a 4 x 4 Latin Square design. Each cow received 6 kg day-1 of a concentrate formulated with 0 (control), 1.3, 2.6 or 3.9 kg of roa...