Evaluation of rumen-protected methionine in lactating dairy cows

Methionine is the first limiting amino acid for milk and protein production in lactating dairy cows (Holstein) fed corn-based diets. A field trial was conducted on a commercial farm to evaluate the effect of supplementing a rumen-protected methionine product (Timet®; VETAGRO S.p.A.; Reggio Emilia, Italy) on lactation performance in highyielding dairy cows. Ninety-nine multiparous Holstein cows were used in a 3-period switchback design: Control 1 (CTR1, 21days, d), Timet® (TMT, 21-d) and CTR2 (12- d). All the cows that entered the study were between 0 and 120 DIM. Cows were fed a TMR formulated to provide 16.7 % CP, 29% Starch, and 32% NDF with 2793 g/d of MP and 2,93 of Lys:Met. During TMT treatment, Timet® was supplemented 25g/d per head. Milk yield was recorded daily and milk was sampled for protein, fat, and urea every 2 days. Data were analyzed using MIXED model procedures including cow as random effect (JMP pro 13®). Although there was not significant difference in milk yield, milk protein was significantly increased by TMT (3.43%) compared to CTR1 (3.35%) and CTR2 (3.38%) (P<0.05), and milk fat was also significantly increased by TMT (3.75%) compared with CTR1 (3.63%) and CTR2 (3.71%); (P<0.05). During TMT treatment it was possible to observe a trend in lowering milk urea (180.8 mg/L) compared to CTR1 (193.0 mg/L) and CRT2 (189.9 mg/L) (P=0.43). In conclusion, addition of Timet® to a corn-based diet increased milk protein and fat concentration and reduced milk urea, thus improving the nitrogen metabolism.