Lasalocid effects on ruminal degradation of protein and postruminal supply of amino acids in Holstein steers.

Five ruminally and duodenally cannulated Holstein steers (305 kg) were used in a switchback experiment with three periods to evaluate two experimental treatments: a basal diet with or without 45 ppm of lasalocid. The basal diet contained approximately 43% rolled corn, 45% alfalfa hay, and 10% soybean meal (DM basis). Lasalocid did not affect feed intake or ruminal digestion of OM and NDF. Ruminal digestion of ADF tended to increase with supplemental lasalocid. Total tract digestion of OM, NDF, ADF, and N and intestinal flow of amino acids were not affected by lasalocid. Also, the ratio of microbial to nonmicrobial N fractions at the duodenum remained unchanged. Ruminal pH and concentrations of NH3, VFA, peptides, and amino acids were not affected by lasalocid. Ruminal protease activity decreased with supplemental lasalocid, but this decrease was not reflected in other variables, such as ruminal concentrations of peptides and amino acids. Ruminal deaminase activity remained unchanged. Thus, we concluded that dietary lasalocid did not alter ruminal protein degradation or postruminal flow of amino acids.