Monensin and Tylosin in a High Energy Diet for Finishing Steers

Abstract

One-hundred-seventy-six Hereford, Angus and Hereford × Angus yearling steers averaging 355 kg were fed in a 2 × 4 factorial (0 and 11 ppm tylosin and 0, 5.5, 11.0 and 33.0 ppm monensin), 127-day finishing experiment to investigate efficacy and safety of combinations of these additives. Steers were lot fed a high energy diet comprised of corn, dehydrated sugarbeet pulp with molasses, cubed alfalfa hay, vitamins and trace mineralized salt. Daily gains (1.48 kg and 1.46 kg) by steers fed 5.5 and 11.0 ppm monensin were slightly greater than by those fed no monensin (1.43 kg), whereas 33.0 ppm depressed (P<.05) rate of gain (1.36 kg). Daily gains were not affected by tylosin (1.43 kg and 1.44 kg for 0 and 11.0 ppm). Daily DM intake and DM intake as a percent of body weight decreased as monensin dosages increased. Average feed DM conversion was improved 5.5% by all levels of monensin. Tylosin did not improve feed efficiency. Rumen fluid from steers fed monensin at 33 ppm contained more propionate than from steers fed 11 ppm but not more than those fed 0 and 5.5 ppm. Total VFA (m moles/liter) was not significantly affected by monensin dosages. Carcass cutability scores for monensin-fed steers were slightly higher than for the controls; heart-kidney-pelvic (HKP) fat percentages and fat thickness were apparently lower; yield grades slightly improved. Other USDA Carcass Data Service evaluations revealed no differences due to the additives. Tylosin markedly reduced the incidence and severity of liver abscesses. There was no interaction of monensin and tylosin for any of the variables.