Chloroform decreases rumen methanogenesis and methanogen populations without altering rumen function in cattle

Anthropogenic CH4 emissions are widely recognised as a world wide problem due to their global warming potential and because they represent a loss of dietary energy to ruminants. Few recent studies have examined medium or long term effects of methanogen inhibitors on rumen functional parameters and development of resistance to them. The aim of our study was to investigate medium term effects of a potent methanogen inhibitor on methanogen populations using molecular techniques and rumen function. Six rumen fistulated cows were divided into two groups and allocated to control and chloroform treatment and fed at a fixed rate of 8.4 kg dry matter (DM)/cow/d. After 7 d of acclimatization. treatment cows were dosed daily with 1.5 ml of chloroform in 30 ml of sunflower oil for 42 d, while control cows only received sunflower oil. Key indicators of rumen function monitored included rumen pH, rumen fill, apparent feed digestibility, apparent rumen digesta retention time, total protozoa numbers, and volatile fatty acid (VFA) and NH3 concentrations. Methane emissions were monitored using the SF6 tracer technique, and methanogens using denaturing gradient gel electrophoresis (DGGE) and four clone libraries. Methanogens and acetogens were monitored in a single cow by most probable number culturing methods. Chloroform, a known inhibitor of methanogenesis, resulted in an immediate and dramatic decrease in CH4 emissions and methanogen numbers, with the effect being most pronounced 1 wk after the start of the treatment. Thereafter, CH4 emissions increased slowly, reaching 62% of pre-treatment levels by d 42. The effect on CH4 emissions was reflected by a near complete disappearance of DGGE bands associated with methanogens in treated cows. This response was particularly obvious for Methanobrevibacter species. There were no effects of chloroform on apparent rumen digesta retention time, apparent feed digestibility, pH. NH3 or rumen fill. Total protozoa numbers tended to increase during the study in both groups. Total VFA concentrations did not change with chloroform treatment, but the acetate:propionate ratio during the period of dosing was lower (P<0.01) for treated cows (1.9) in the middle of the study (d 23) than in the control cows (2.7), but did not differ after treatment ceased at d 53. Despite profound effects of chloroform on CH4 emissions and methanogens, chloroform did not appear to alter basic rumen function. Whether a reduction in CH4 loss improves feed conversion efficiency requires further research using substances which have a sustained anti-methanogenic effect. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture - Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. (C) 2011 Elsevier B.V. All rights reserved.