This study evaluated the feeding behavior of lactating cows on pasture of Brachiaria (Urochloa) decumbens fed with concentrate supplementation containing different levels of castor meal inclusion treated with calcium hydroxide Ca (OH) 2, in the proportions of 0; 3.3; 6.6 to 10% of the total diet. Eight cows (degree of blood ½ to ¾ Holstein x Zebu), with previous average production of 3000-4000 kg adjusted to 300 days of lactation and average body weight of 465.16 kg ± 65.45 kg were distributed in two 4 x 4 Latin squares. The behavior was assessed every five minutes for 24 hours on the 21st day of each period. The results were tested by analysis of variance and regression at p < 0.05 probability. The time spent in grazing, rumination, idle and in the trough; total chewing time, number of cuds per day, chewing per day; chewing per cud; the number of periods of grazing, rumination, idle and in the trough; time spent by period of grazing, rumination, idle and in the trough were not different between treatments. The feed efficiency (g DM h-1; g NDFa h-1 and g TDN h-1) and time spent per cud ruminated TSR sec cud-1) were linearly reduced. It is recommended to include up to 10% castor meal treated with Ca (OH)2 in the total diet.