The best opportunity for operations in our traditional production system to impact methane production from their cattle may be in the growing phase, where up to 6% of gross energy intake can be lost as methane, compared with only 2-3% of GE in the finishing phase (Johnson et al., 1995). Dietary changes such as increasing concentrate vs. forage content, addition of dietary fats, and use of ionophores, among other strategies have proven useful in decreasing methane production (Hristov et al., 2013).
A 120-steer, individually-fed growing study at UNL (Pesta et al., 2014) evaluated the effects of forage quality, level of modified distillers grains (MDGS), and presence or absence of monensin on methane production, volatile fatty acid (VFA) profile, and performance. Gas samples (which are a mixture of exhaled breath from steers and ambient air) were collected at feeding, periodically throughout an 84 day study. Volatile fatty acid profile was evaluated using rumen fluid collected via esophageal tubing on day 21 and 63, prior to feeding.
Methane data is expressed as a ratio of methane to carbon dioxide (CH4:CO2) where CO2 can be used as an internal marker since its production is relatively constant across cattle of similar size, type, and production level (Madsen et al., 2010).
Forage quality had the greatest impact on methane emissions, as those fed a blend of alfalfa and sorghum silage had an 11.5% greater CH4:CO2 than those fed ground corn stalks. This is due to a greater intake of a more readily-digestible fiber, which produces more methane.
It is important to realize, however that the cattle fed the high-quality forage also had improved gain and feed conversion, so further calculation of methane per unit of gain produced will be important. Level of MDGS in the diet (0, 20, or 40%) had no effect on CH4:CO2, as methane emissions still depended almost entirely on type of forage.
The effect of monensin was more complex. The addition of monensin decreased CH4:CO2 in low-quality forage diets, but had no effect in high-quality diets. Effects on acetate to propionate ratio were minimal; as 40% MDGS lowered A:P compared to 0% MDGS, while forage quality and monensin had little impact.
Performance was improved by use of high-quality forage and MDGS, while response to monensin was variable across basal diet type. Response of methane concentration and VFA profile due to diet was variable and subject to multiple interactions, reflecting the complexity of the microbial processes involved within the rumen.
- Hristov, A. N., J. Oh, J. L. Firkins, J. Dijkstra, E. Kebreab, G. Waghorn, H. P. S Makkar, A. T. Adesogan, W. Yang, C. Lee, P. J. Gerber, B. Henderson, and J. M. Tricarico. 2013. Mitigation of methane and nitrous oxide emissions from animal operations: I. A review of enteric methane mitigation options. J. Anim. Aci. 91: 5045-5069.
- Johnson, K. A. and D. E. Johnson. 1995. Methane emissions from cattle. J. Anim. Sci. 73:2483-2492.
- Madsen. J, B. S. Bjerg, T. Hvelplund, M. R. Weisbjerg, and P. Lund. 2010. Methane and carbon dioxide ratio in excreted air for quantification of the methane production from ruminants. Livestock Sci. 129: 223-227.
- Pesta, A. C., A. K. Watson, S. C. Fernando, and G. E. Erickson. 2014. Effects of forage quality, MDGS, and monensin on performance, methane concentration, and ruminal fermentation of growing cattle. Nebraska Beef Cattle Rep. MP 99:29-31.