1Department of Animal and Food Sciences, College of Agricultural and Natural Resources, University of Delaware , Newark, Delaware, USA1, Balchem Corporation , New Hampton, New York, USA2

Differences in the encapsulation technology used to protect methionine products may impact their rumen degradation and intestinal availability. The objective of this study was to determine the effect of a lipid encapsulated methionine prototype on milk, milk protein and casein yields. The study was conducted as a replicated 5 x 5 Latin square design with 5 multiparous and 5 primiparous Holstein cows assigned to either a negative control ration (NC) deficient in metabolizable (MP) methionine (-16.2 g/d), NC supplemented with Smartamine M (SM, Adisseo, Antony, France) or the NC supplemented with a methionine prototype containing 70% D,L-methionine at three different inclusion levels (M1, M2, M3, Balchem Corporation, New Hampton, NY) containing 100%, 125%, and 150%, respectively, of methionine that is in Smartamine M. The ration was balanced using NDS assuming 28 kg/d DMI, 50 kg/d milk, 3.80% fat, 2.90% protein, and 707 kg bodyweight. Periods were 14 days and milk samples were collected on days 11-14 of each period. Data collected during the last four days of each period were averaged by cow and analyzed using the Glimmix procedure of SAS. The model included a covariate (data collected during a 2-week standardization period), fixed effects of treatment, period, parity and the interaction of treatment × parity and the random effect of cow. Treatment affected protein percentage (P=0.03) and casein percentage (P=0.05) (Table 1). Compared to the NC, SM, M2 and M3 treatments increased protein percentage and casein percentage suggesting that the M2 and M3 treatments were equally as effective as Smartamine M.