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Applied and Environmental Microbiology, January 2009, p. 374-380, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.01672-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Long-Term Monensin Supplementation Does Not Significantly Affect the Quantity or Diversity of Methanogens in the Rumen of the Lactating Dairy Cow

S. E. Hook,^1* K. S. Northwood,² A.-D. G. Wright,^1,2 and B. W. McBride¹

Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada,¹ CSIRO Livestock Industries, Queensland Bioscience Precinct, 306 Carmody Rd., St. Lucia, Queensland 4067, Australia²

Received 18 July 2008/ Accepted 14 November 2008

A long-term monensin supplementation trial involving lactating dairy cattle was conducted to determine the effect of monensin on the quantity and diversity of rumen methanogens in vivo. Fourteen cows were paired on the basis of days in milk and parity and allocated to one of two treatment groups, receiving (i) a control total mixed ration (TMR) or (ii) a TMR with 24 mg of monensin premix/kg of diet dry matter. Rumen fluid was obtained using an ororuminal probe on day –15 (baseline) and days 20, 90, and 180 following treatment. Throughout the 6-month experiment, the quantity of rumen methanogens was not significantly affected by monensin supplementation, as measured by quantitative real-time PCR. The diversity of the rumen methanogen population was investigated using denaturing gradient gel electrophoresis (DGGE) and 16S rRNA clone gene libraries. DGGE analysis at each sampling point indicated that the molecular diversity of rumen methanogens from monensin-treated cattle was not significantly different from that of rumen methanogens from control cattle. 16S rRNA gene libraries were constructed from samples obtained from the rumen fluids of five cows, with a total of 166 clones examined. Eleven unique 16S rRNA sequences or phylotypes were identified, five of which have not been recognized previously. The majority of clones (98.2%) belonged to the genus Methanobrevibacter, with all libraries containing Methanobrevibacter strains M6 and SM9 and a novel phylotype, UG3322.2. Overall, long-term monensin supplementation was not found to significantly alter the quantity or diversity of methanogens in the rumens of lactating dairy cattle in the present study.

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* Corresponding author. Mailing address: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Phone: (519) 824-4120, ext. 53436. Fax: (519) 836-9873. E-mail: shook{at}uoguelph.ca

Published ahead of print on 21 November 2008.

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Applied and Environmental Microbiology, January 2009, p. 374-380, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.01672-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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