Influence of Ionophores on Nutrient Utilization in Ruminants

Abstract

Eleven steers that were fitted with permanent ruminal, duodenal and ileal cannulae were used to compare effects of ionophores (monensin or lasalocid) and level of corn (20 or 80%) on site and extent of starch, fiber, energy, crude protein and mineral digestion. Ruminal -N concentration was higher (P .05) for steers fed 20% corn. Steers fed monensin or lasalocid had higher (P .05) rumen -N than control steers. Ruminal, small intestine and total tract OM digestion was higher (P .01) in steers fed the 80% corn diet. Steers fed monensin or lasalocid had lower (P .01) true OM digestion in the rumen but higher (P .01) intestinal digestion of OM. Steers fed the high grain diet had lower (P .01) ruminal and higher (P .01) small intestine digestion of starch. Feeding monensin or lasalocid decreased (P .01) ruminal and increased (P .01) small and large intestine digestion of starch. Digestion of NDF in the total tract was higher (P .01) in steers fed the 20% grain diet. Steers fed the 20% corn diet had higher (P .01) ruminal, large intestinal and total tract digestion of cellulose. Hemicellulose digestion was higher (P .10) in large intestines of steers fed the lower corn diet. Steers fed monensin or lasalocid had higher (P .01) ruminal, small intestine and total tract digestions of NDF. Duodenal N flow was higher (P .10) in steers fed the 80% corn diet. Steers fed monensin or lasalocid had higher (P .10) dietary N flows to the duodenum than those fed the control diet. More gross energy was digested in the large intestine and total tract of steers fed the higher grain diet. Small intestine and total tract digestion of Ca were lower (P .01) in steers fed the higher grain diet. Steers fed monensin or lasalocid had higher (P .01) digestion of Ca in the small intestine than control steers. Steers fed the higher grain diet digested more (P .01) P in the small intestine and total tract. Ruminal digestion of P was lower (P .01) in steers fed ionophores. Feeding the high grain diet increased the digestion of Mg, K, Fe and Zn in the total tract.