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Tylosin Boluses for Grazing Beef Steers¹

University of Kentucky, Lexington

Abstract

This study was conducted to investigate tylosin as a potential growth stimulant when given in sustained release boluses to grazing steers implanted with stilbestrol. Eighty-one steers which were given tylosin boluses at 42-day intervals during four trials gained 9.2% faster (P<.005) than 80 control steers.

Treated steers consistently gained faster (0.17 kg. per steer daily) than control steers during the first 14 days after bolus administration. Smaller and more variable differences in gain were observed between the control and treated steers from 14 to 28 and from 28 to 42 days after bolusing. Results of bolus recovery studies and assays of rumen fluid for the tylosin indicated that the variable growth response of treated steers during different times after bolus treatment was due to failure of the boluses to provide a uniform daily level of tylos in for the steers.

¹ The investigation reported in this paper (67-5-72) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.

² Present address: Auburn University, Auburn, Alabama.