Background
The authors write that maize (a C4 crop) "is one of the most important feedstuffs for ruminants but studies investigating the combined effects of drought and CO2 elevation on the plant and its fermentation in the rumen are scarce," citing Loholter et al. (2012); and they thus state that "there is an urgent need to investigate the effect of climate change, i.e., increase of atmospheric CO2 and of summer drought on rumen fermentation in a more detailed way."

What was done
In a FACE study conducted at an experimental field of the Federal Research Institute for Rural Areas, Forestry and Fisheries, which is located in Braunschweig (Germany), Meibaum et al. grew maize (Zea mays L., cv. Romario) at atmospheric CO2 concentrations of either 380 or 550 ppm, and at either 170 or 330 mm of total growing-season water supply. Then, at the end of the growing season, whole maize plants were harvested and representative samples of each of them were analyzed for crude nutrients, neutral detergent fiber, acid detergent fiber and acid detergent lignin (ADL). In addition, in an in vitro experiment using the semi-continuous rumen-simulation technique (RUSITEC), as originally described by Czerkawski and Breckenridge (1977), they studied the effects of atmospheric CO2 enrichment on rumen fermentation patterns.

What was learned
The six German researchers report that "the Bacteria- and Archaea-specific SSCP [single strand conformation polymorphism] profiles as well as the production rates of short-chain fatty acids and their molar percentages were not affected by [the various] treatments." They also state that "the digestibilities of organic matter obtained from the present experiment (45%-48%) are consistent with the results from RUSITEC experiments carried out by other authors (Czerkawski, 1986; Klevenhusen et al., 2009; Hildebrand et al., 2010)." And they additionally indicate that "the CO2 treatment had no effect on digestibility of organic matter, which is in agreement with the findings of Akin et al. (1994), who studied the effect of elevated CO2 on sudan grass," which is another C4 plant.

What it means
Meibaum et al. conclude that "changes in forage due to climate change will not result in significant alterations of rumen microbial community because of its pronounced ability of dynamic adaptation," and, therefore, they suggest that "most parameters of rumen digestion will only be slightly influenced by plant material altered as a result of climatic changes."

References
Akin, D.E., Kimball, B.A., Mauney, J.R., LaMorte, R.L., Hendrey, G.R., Lewin, K., Nagy, J. and Gates, R.N. 1994. Influence of enhanced CO2 concentration and irrigation on sudan grass digestibility. Agricultural and Forest Meteorology 70: 279-287.

Czerkawski, J.W. 1986. An Introduction to Rumen Studies. Pergamon Press Ltd., Oxford, United Kingdom.

Czerkawski, J.W. and Breckenridge, G. 1977. Design and development of a long-term rumen simulation technique (Rusitec). British Journal of Nutrition 38: 371-384.

Hildebrand, B., Boguhn, J. and Rodehutscord, M. 2010. Effect of maize silage to grass silage ratio and feed particle size on ruminal fermentation in vitro. Animal Feed Science and Technology 5: 528-536.

Klevenhusen, F., Bernasconi, S.M., Hofstetter, T.B., Bolotin, J., Kunz, C. and Soliva, C.R. 2009. Efficiency of monolaurin in mitigating ruminal methanogenesis and modifying C-isotope fraction when incubating diets composed of either C3 or C4 plants in a rumen simulation technique (Rusitec) system. British Journal of Nutrition 102: 1308-1317.

Loholter, M., Meyer, U., Manderscheid, R., Weigel, H.J., Erbs, M., Flachowsky, G. and Danicke, S. 2012. Effects of free air carbon dioxide enrichment and drought stress on the feed value of maize silage fed to sheep at different thermal regimes. Archives of Animal Nutrition 66: 335-346.