Document Type


Report Number

A.S. Series 73-31

Publication Date



A period of adaptation to urea during which feedlot performance is suppressed is frequently experienced when this product is added to rations of cattle not previously, or recently, fed it. This effect appears more evident with levels of urea used when it forms a major part of total protein in the ration. Urea and antibiotics in combination are common additions to protein supplements or mixed rations. At usual levels for continuous feeding of antibiotics and safe levels of urea for the dietary conditions, the combination appears satisfactory and to offer the beneficial effects from these compounds after a suitable period of urea adaptation. However, much less is known about the effects of high levels of antibacterial compounds and urea together during early stages in the feedlot with unadapted cattle. More research is needed to answer questions concerning levels of these compounds during early stages in the feedlot, especially with calves shipped at weaning or a few weeks thereafter. Other information needed includes the relative effects of adaptation to urea and antibacterial singularly and together after various times of arrival of the cattle at the feedlot. Effects of adding urea to furnish the major source of supplemental protein to a corn silage ration for calves at various times following arrival at the feedlot were investigated in this experiment. Urea additions were made to rations of calves fed with and without antibacterial compounds.

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Department of Animal Science, Agricultural Experiment Station, South Dakota State University