2011 Annual Report 1a.Objectives (from AD-416) The objective of this trust is to quantify the effectiveness of feeding the isobutyl ester of 2-hydroxy, 4-methylthio butyrate (aka HMBi), a methionine supplement sold commercially by Adisseo as MetaSmart®. Feeding this supplement may allow dairy cows to be fed less dietary crude protein without lowering production. If successful in practice, then urinary nitrogen output, the most polluting form of excretory nitrogen, would be reduced. 1b.Approach (from AD-416) In vitro studies will be conducted using batch cultures of mixed ruminal microorganisms to assess effects of methionine, HMB and HMBi on kinetics of ammonia uptake, total amino, and VFA concentration patterns, organic matter and NDF digestion, microbial protein formation, and protozoal numbers. A large-scale in vivo study will be conducted with lactating dairy cows which are fed a low-protein diet based on typical feeds to determine the effects of supplementing HMB, HMBi, or rumen-protected methionine on milk production, nitrogen efficiency, and ruminal metabolism. 3.Progress Report This project is related to the following objective and sub-objective of the parent project: Objective 1. Improve accuracy, reproducibility, and ease of measuring/estimating feed digestibility; sub-objective 1.B.: Develop and evaluate in vitro methods for assessment of ruminal degradability of dietary proteins. Findings from the initial lactation study, previously reported to cooperators, were published in a peer-reviewed paper in the Journal of Dairy Science. The animal phase of a large-scale follow-up trial that tested the effectiveness of the methionine precursors was completed in January 2010; all production results from this trial have been analyzed. Also, chemical analyses of the omasal samples collected during this follow-up study are being completed. Monitoring of our activities with the cooperator was accomplished via a site-visit, e-mail messages throughout the year, and a face-to-face discussion at the annual American Dairy Science Association meeting in New Orleans, LA.