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In Argentine grazing systems, additional supply of energy and protein is needed to balance the diet during periods of pasture shortage in winter. Three protein meal sources were evaluated, in terms of milk yield and composition, for grazing dairy cows receiving a supplementary PMR. Thirty three multiparous cows, averaging 75 ± 15 DIM, and over 7000 L/cow in previous lactations, were randomly assigned to 3 treatments: SM= soybean meal, L-SuM= sunflower meal-low-protein and CM= canola meal, in a continuous split-plot design with covariance analysis. The diets were isoenergetic (1.82 Mcal NEL) and isonitrogenous (17% CP), and were formulated (DM basis) with 17 % pasture and 83% of a PMR containing corn silage, alfalfa hay, corn grain, minerals and vitamins premix and the corresponding protein meal. The CP concentrations were 28, 35 and 41% for L-SuM, CM and SM, and represented 25, 20 and 15% total diet DM, respectively. Table 1 shows milk yield and composition for all treatments. The L-SM had the lowest response in terms of milk yield, but the highest in milk fat percentage, thus suggesting concentration effects. On the other hand, CM produced the lowest protein concentrations, probably because of differences in dietary amino acid supply to the mammary gland. Milk urea concentration was lowest for CM. [ABSTRACT FROM AUTHOR]