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Cattle selected for lower residual feed intake have reduced daily methane production^1,2

R. S. Hegarty^*,3, J. P. Goopy^,4, R. M. Herd^* and B. McCorkell

^* New South Wales Department of Primary Industries, Beef Industry Centre, Armidale, New South Wales 2351, Australia; and University of New England, Armidale, New South Wales 2351, Australia; and and Tamworth Agricultural Institute, Tamworth, New South Wales 2340, Australia

³ Corresponding author: roger.hegarty{at}dpi.nsw.gov.au

Seventy-six Angus steers chosen from breeding lines divergently selected for residual feed intake (RFI) were studied to quantify the relationship between RFI and the daily rate of methane production (MPR). A 70-d feeding test using a barley-based ration was conducted in which the voluntary DMI, feeding characteristics, and BW of steers were monitored. The estimated breeding value (EBV) for RFI (RFI_EBV) for each steer had been calculated from 70-d RFI tests conducted on its parents. Methane production rate (g/d) was measured on each steer using SF₆ as a tracer gas in a series of 10-d measurement periods. Daily DMI of steers was lower during the methane measurement period than when methane was not being measured (11.18 vs. 11.88 kg; P = 0.001). A significant relationship existed between MPR and RFI when RFI (RFI_15d) was estimated over the 15 d when steers were harnessed for methane collection (MPR = 13.3 x RFI_15d + 179; r² = 0.12; P = 0.01). Animals expressing lower RFI had lower daily MPR. The relationship established between MPR and RFI_15d was used to calculate a reduction in daily methane emission of 13.38 g accompanied a 1 kg/d reduction in RFI_EBV in cattle consuming ad libitum a diet of 12.1 MJ of ME/kg. The magnitude of this emission reduction was between that predicted on the basis of intake reduction alone (18 g·d^–1·kg of DMI^–1) and that predicted by a model incorporating steer midtest BW and level of intake relative to maintenance (5 g·d^–1·kg of DMI^–1). Comparison of data from steers exhibiting the greatest (n = 10) and lowest (n = 10) RFI_15d showed the low RFI_15d group to not only have lower MPR (P = 0.017) but also reduced methane cost of growth (by 41.2 g of CH₄/kg of ADG; P = 0.09). Although the opportunity to abate livestock MPR by selection against RFI seems great, RFI explained only a small proportion of the observed variation in MPR. A genotype x nutrition interaction can be anticipated, and the MPR:RFI_EBV relationship will need to be defined over a range of diet types to account for this.

Key Words: beef cattle • feed conversion efficiency • genetics • methane production

² The assistance provided by R. Woodgate, S. McClelland, J. Brunner, W. Johns, and S. Sinclair of NSW Department of Primary Industries, as well as R. Geddes of the University of New England, and M. Wolcott of the Cooperative Research Centre for Cattle and Beef Quality is acknowledged.

⁴ J. P. Goopy was supported by a postgraduate scholarship funded by Meat and Livestock Australia.

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