EFFECT OF MONENSIN AND MONENSIN AND TYLOSIN COMBINATION ON FEED-INTAKE VARIATION OF FEEDLOT STEERS

A trial involving four commercial feedlots and an individual feeding t rial evaluated the effect of monensin and monensin/tylosin on intake v ariation and deaths from digestive disorders. Four commercial feedlots in Texas and Colorado fed 2,904 yearling crossbred steers (340 kg) hi gh-grain diets containing approximately 82% grain, 8% silage and alfal fa hay, 4% fat, and 6% supplement (DM basis). Steers were allotted ran domly to one of three monensin/tylosin levels: 1) no monensin or tylos in (control); 2) 22 mg/kg of monensin and 11 mg/kg of tylosin; or 3) 3 3 mg/kg of monensin and 11 mg/kg of tylosin. Monensin/tylosin reduced DMI (P < .05) and improved ADG (P < .05) and feed efficiency (P < .01) . Intake variation associated with dry matter offered per pen was not different among treatments. In the individual feeding trial, feeding 2 7 mg/kg of monensin reduced (P < .10) DMI variation during grain adapt ation and during d 57 to 70 and d 97 to 110 compared with the control (no monensin) diet. The magnitude of intake variance was 5 to 10 times greater with individually fed steers than with steers fed in the comm ercial feedlot pens. When the DMI of the individually fed steers were averaged and treated as a pen of steers, DMI variance was reduced dras tically and was not different between treatments. We interpret these d ata to indicate that monensin and monensin/tylosin reduce feed intake variation among individual steers within a pen of steers. Pen means ma sk individual animal variation to the point that it is difficult to de tect treatment differences.