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Methane production and methanogen levels in steers that differ in residual gain

H. C. Freetly, A. K. Lindholm-Perry, K. E. Hales, T. M. Brown-Brandl, M. Kim, P. R. Myer, J. E. Wells
Journal of animal science 2015 v.93 no.5 pp. 2375-2381
Methanomicrobiales, bacteria, calorimetry, cecum, digestive tract, energy intake, feed conversion, feed intake, fermentation, greenhouse gases, liveweight gain, methane, methane production, methanogens, rectum, rumen, rumen bacteria, rumen fermentation, steers
Methane gas released by cattle is a product of fermentation in the digestive tract. The two primary sites of methane fermentation in ruminants are the reticulum-rumen complex, and the cecum. Methane release from cattle represents a 2 to 12% loss of the energy intake. Reducing the proportion of feed energy lost as methane (CH4) has the potential of improving feed efficiency as well as decreasing the contribution of cattle to greenhouse gas production. Feed intake and growth were measured on 132 fall-born steers for 70 d. Seven steers with extreme positive residual gain (RG) and 7 steers with extreme negative RG whose dry DMI was within 0.32 STD of the mean DMI were selected for subsequent measurements. Enteric methane production was measured via indirect calorimetry. Rumen, cecum, and rectal contents were obtained from steers at slaughter for measurement of in vitro methane production and methanogen levels. Enteric methane production did not differ (P = 0.11) between the positive RG (628 ± 73 mol/6 h) and the negative RG (415 ± 73 mol/6 h) steers. In vitro rumen methane production did not differ between steers with different RG (P = 0.98). In vitro methane production was greater in the rumen (0.510 ± 0.051 CH4 nmol·DM g-1·min-1) than cecum (0.036 ± 0.051 CH4 nmol·DM g-1·min-1; P < 0.001). Methanogens as a percentage of the total bacteria did not differ between RG groups (P = 0.18). The percentage of methanogens in rumen content (5.3 ± 3.1%) did not differ from the cecum content (11.8 ± 3.1%; P = 0.14). The percentage in the rectum content (0.7 ± 3.1%) was not different than the rumen content (P = 0.29), and was lower than the cecum content (P = 0.01). The order Methanomicrobiales as a percentage of total methanogens did not differ across sample sites (P = 0.81); however, steers with negative RG (8.3 ± 2.5%) had more compared to steers with positive RG (3.5 ± 2.5%). Cattle that differ in RG at the same DMI do not differ in characteristics associated with methane production.