Journal of Animal Science, Vol 73, Issue 1 39-44, Copyright © 1995 by American Society of Animal Science

JOURNAL ARTICLE

Effect of monensin and monensin and tylosin combination on feed intake variation of feedlot steers

R. A. Stock, S. B. Laudert, W. W. Stroup, E. M. Larson, J. C. Parrott and R. A. Britton
Department of Animal Science, University of Nebraska, Lincoln 68583-0908.

A trial involving four commercial feedlots and an individual feeding trial evaluated the effect of monensin and monensin/tylosin on intake variation and deaths from digestive disorders. Four commercial feedlots in Texas and Colorado fed 2,904 yearling crossbred steers (340 kg) high-grain diets containing approximately 82% grain, 8% silage and alfalfa hay, 4% fat, and 6% supplement (DM basis). Steers were allotted randomly to one of three monensin/tylosin levels: 1) no monensin or tylosin (control); 2) 22 mg/kg of monensin and 11 mg/kg of tylosin; or 3) 33 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 27 mg/kg of monensin reduced (P < .10) DMI variation during grain adaptation 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 commercial feedlot pens. When the DMI of the individually fed steers were averaged and treated as a pen of steers, DMI variance was reduced drastically and was not different between treatments. We interpret these data to indicate that monensin and monensin/tylosin reduce feed intake variation among individual steers within a pen of steers. Pen means mask individual animal variation to the point that it is difficult to detect treatment differences.

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