Effects of alimet on nutrient digestibility, bacterial protein synthesis, and ruminal disappearance during continuous culture

A dual effluent continuous culture system was used to investigate the effects of inclusion of Alimet (Novus International, Inc., St. Louis, MO) feed supplement [an 88% aqueous solution of dl, 2-hydroxyd-4-(methylthio) butanoic acid (HMB)] in the diet on nutrient digestibility, bacterial protein synthesis and ruminal disappearance of HMB. Four fermenters were fed three times daily a basal diet that consisted of 50% grain mixture and 50% forage for 9 d. In experiment 1, four concentrations of HMB (0, 0.20, 0.77, and 1.43% DM basis) were added to the diet and fed to the fermenters twice daily. In experiment 2, two concentrations of dietary HMB (0 and 0.88% DM basis) were fed twice daily and evaluated with two solids retention times (16.7 vs. 25.0 h) and two liquid dilution rates (0.15 vs. 0.125 h(-1)). Increasing the amount of HMB in the diet did not affect nutrient digestibility, volatile fatty acid concentrations, or ruminal escape of HMB. Bacterial protein synthesis was improved with the addition of HMB during high and low retention times. The extent of HMB escaping ruminal degradation ranged from 21.6 to 43.2% and was highest at the lower retention time. It can be concluded that a fraction of HMB survives rumen microbial degradation and, therefore, provides a rumen-protected form of methionine at the same time that it improves bacterial protein synthesis.