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

Abstract

ABSTRACT 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