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Effect of Monensin on Breakdown of Protein by Ruminant Microorganisms in Vitro^{1 ,2,}

University of Illinois, Urbana 61801

Abstract

The effects of monensin on N metabolism by ruminal microorganisms in a semicontinuous culture system were determined. Rumen fluid inoculum was obtained from steers fed a hay-concentrate diet (60:40 ratio on a dry matter basis) containing 3 3 ppm monensin. Treatments were 0, 1 and 4 mg monensin/kg of incubation mixture, with starch, glucose, cellulose and casein used as the energy and protein sources. Casein degradation decreased linearly (P<.01) with increasing levels of monensin, as did production of ammonia-N (P<.05) and microbial N (P<.01). Increases were observed in nonammonia, nonmicrobial N (P<.01), alpha-amino N (P<.10) and total peptides (P<.001). The culture supernatant was fractionated on a Sephadex G-10 column to separate peptides. With the 4 mg/kg treatment, the percentage of the total ninhydrin positive material eluted at an elution volume:void volume ratio of 1.5 or less was greater than the percentage eluted with the 0 or 1 mg/kg treatments (P<.025). Acetate production and molar proportion decreased (P<.001), while propionate production was unchanged. Methane production decreased slightly (P<.10). Cellulose degradation was markedly inhibited (P<.001) by monensin treatment.

¹ The research reported herein was supported in part by a grant from Lilly Research Laboratories Division of Eli Lilly and Company, Greenfield, IN.

² The research reported herein is part of the thesis submitted by the senior author in fulfillment of the requirements for the Master of Science Degree in Dairy Sci., Univ. of Illinois, Urbana-Champaign, 1980.