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Comparative effects of multiple sources of rumen-protected methionine on milk production and serum amino acid levels in mid-lactation dairy cows

Zang, Y., Samii, S. Saed, Phipps, Z.C., Tager, L.R., McFadden, J.W., Krause, K.M.
The Professional animal scientists 2017 v.33 no.6 pp. 692-699
Holstein, alfalfa, blood serum, corn silage, dairy cows, dairy industry, haylage, lactose, lysine, methionine, milk, milk fat, milk proteins, milk yield, new products, protein content, urea nitrogen
The dairy industry demand for rumen-protected methionine (RP-Met) supplements has been competitive because of the constant emergence of new products. To evaluate performances, our study was designed to characterize the production response of 3 RP-Met supplements in mid-lactation dairy cows. Twelve multiparous Holstein cows were used in a replicated 4 × 4 Latin square design with 21-d treatment period. Treatments included control [(basal) diet based on corn silage and alfalfa haylage, supplemented with 0.025% of ration DM of lysine (Lys; Ajipro)] or 1 of 3 RP-Met supplements [Smartamine M (SMM), Mepron M85 (MM85), or Novimet (NVM)]. For RP-Met groups, Met and Lys were supplemented to the basal diet at 0.03 and 0.20% of ration DM, respectively. Treatments had no effect on DMI or milk yield. Treatment did not modify milk fat or lactose concentration; however, milk protein content was elevated with SMM, relative to control or NVM (3.30% vs. 3.24 or 3.24%, respectively; P < 0.05). Milk fat, protein, and lactose yield were not modified by treatments. Treatments tended (P = 0.12) to affect milk urea nitrogen. Serum Met concentration increased for SMM compared with control, MM85, or NVM (27.3 μM vs. 21.2, 23.3, or 22.7 μM, respectively; P < 0.001). Similarly, supplementation of SMM reduced the serum Lys:Met ratio (4.5:1) compared with control (5.2:1), MM85 (5.1:1), or NVM (5.2:1) (P < 0.05). Treatment did not modify the serum levels of all other EAA. We conclude that SMM increased circulating Met and milk protein content more effectively than NVM or MM85.