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 ex perimental treatments: a basal diet with or without 45 ppm of lasaloci d. The basal diet contained approximately 43% rolled corn, 45% alfalfa hay, and 10% soybean meal (DM basis). Lasalocid did not affect feed i ntake or ruminal digestion of OM and NDF. Ruminal digestion of ADF ten ded to increase with supplemental lasalocid, Total tract digestion of OM, NDF, ADF, and N and intestinal flow of amino acids were not affect ed by lasalocid. Also, the ratio of microbial to nonmicrobial N fracti ons 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 co ncentrations of peptides and amino acids. Ruminal deaminase activity r emained unchanged. Thus, we concluded that dietary lasalocid did not a lter ruminal protein degradation or postruminal flow of amino acids.