One hundred ninety-two crossbred steers were used in a 2 x 4 factorially arranged
experiment to study the effects of including fat and ionophores in finishing rations. Main effects
were level of supplemental fat (0 or 4% tallow) and ionophore type [none, Bovatece (B),
Rumensine + 'JYlane (RT), or daily rotation of Band RT (BRT)]. Daily feed intake (P<.10)
and daily gain (P<.OO5) were reduced for steers fed R'T, but only when fat was included in the
diet. In diets containing no supplemental fat, RT increased daily gain 10%. RT improved feed
efficiency 8% (P<.05) in nonfat diets, but there was no difference between ionophores in diets
containing fat. Adding fat improved feed efficiency of steers fed no ionophore or B. This study
suggests that response of finishing steers to ionophores can be modified by the inclusion of fat
in the diet.
