The purpose of this work was to evaluate the effect of 8.4 g/day of rumen protected methionine (RPM) or 8.4 g/day of rumen non protected methionine (RNPM) or even of control cows on milk yield and compositon during 90 days of lactation. Six high yielding lactating Holsteins cows (>20 kg/day) in the first and second lactation, with 19 + 6 days of lactation were used in a duplicated latin square design. The cows were fed a total mixed ration composed of corn silage and concentrate. The milk production and the milk protein and yield were not affected by RPM or RNPM suplementation. The milk yield was 27.70; 27.09 and 27.61 kg/day, the milk protein content was 2.83; 2.85 and 2.77% and the protein yield was 0.77; 0.76 and 0.79 kg/day for control cows, RPM and RNPM, respectively. The fat content was affected (P<.05) by RPM suplementation. The fat content was 2.39; 2.12 and 1.89 % for RPM, RNPM and control, respectively. Daily fat milk yield were 0.57; 0.58 and 0.58 and the 3.5% fat correct milk yield were 21.25; 21.19 and 21.35 kg/day, respectively for control, RPM and RNPM, respectively. The suplementation with RPM did not affect the milk yield, but improved milk fat content in early latctation cows.
amino acid; fat percent; methionine; milk yield; protein percent; supplementation
