Methane emissions from grazing Angus beef cows selected for divergent residual feed intake

Residual feed intake (RFI) is the difference between actual feed intake and expected feed intake required for maintenance and production, such as growth of beef cattle and milk production in dairy cattle. RFI has been shown to be linked with a reduction in CH(4) emissions in studies that used grain based diets. Our study quantified CH(4) emissions from 48 Angus cows selected based on estimated breeding values (EBV) for extremes in RFI. These EBV were based on a post weaning RFI test conducted at the Western Australian Department of Agriculture and Food Vasse Research Centre. Two groups of cows with divergent RFI were used being: 25 high RFI (i.e., HRFI, low efficiency) cows with an EBV of 0.68 +/- 0.220 kg/d, and 23 low RFI (i.e., LRFI, high efficiency) cows with an EBV of -0.69 +/- 0.335 kg/d. Methane emissions were measured under grazing conditions in a Western Australian annual pasture production system using the Open Path Fourier Transform Infrared Spectrophotometer (OP-FTIR) technique. A group average emission rate was obtained for the two RFI lines of cows. Each group was measured separately over a two 6 d periods being in the summer when the cows were pregnant and grazing annual pastures of a low dry matter (DM) digestibility of 550 g/kg, and in the winter when the cows were nursing calves and grazing annual pastures with a high DM digestibility of 810 g/kg. It was hypothesised that LRFI cows would produce less CH(4) when grazing both high and low quality pastures. When pregnant and grazing low quality pastures, both groups of cows produced similar amounts of CH(4)/day (0.26 +/- 0.013 versus 0.26 +/- 0.018 g CH(4)/kg of liveweight (LW) for LRFI and HRFI cows respectively. While nursing calves and grazing high quality pastures, there was a difference (P<0.05) in daily CH(4) emissions between the LRFI and HRFI cows of 0.34 CH(4) +/- 0.017 versus 0.46 +/- 0.023 g CH(4)/kg LW). The hypothesis that LRFI cows produce less CH(4) is not supported by results for these cows grazing low quality summer pasture, but it is supported when grazing high quality winter pastures. Results indicate LRFI cattle may have the potential to contribute to reduced CH(4) emissions under grazing systems when provided with a high nutritional quality pasture source. This paper 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 Editor; 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.