Cellulosic biofuel process can also improve ruminant forage digestibility

The Ammonia Fiber Expansion (AFEX) process breaks down cell walls producing a product that can be used for biofuel production or cattle feed.

Research is being conducted at Michigan State University to develop and commercialize a process that mimics what happens in the stomach of ruminant animals. Cattle, sheep and goats can access the sugar contained in cellulose and hemicellulose (in plant cell walls) through a combination of chewing and fermentation that takes place in the rumen (first stomach compartment). Biofuel researchers also want to access the sugars in plant cell walls to convert them to biofuels and have developed a patented process called AFEXTM (AFEX is a trademark of MBI) to improve this process.

Ammonia Fiber Expansion, or AFEXTM, uses anhydrous ammonia in a controlled temperature and pressure reaction to break down plant cell walls, and then, in a separate step enzymes are added to break apart the sugars, just like ruminant animals do.

The corn ethanol industry is well established, producing 13.3 billion gallons in 2012 according to the Renewable Fuels Association, 2013. The next generation biofuel, derived from cellulose and hemicellulose, is just beginning to develop. There is a “chicken and egg” issue to be dealt with. Farmers will not plant large acreages of second generation biofuel crops unless there is a market for their crop. Biofuel producers will not invest in building processing facilities unless they can be assured of a dedicated supply of biomass crops. So which will come first?

Michigan State University Extension reports that AFEXTM treated biomass can also be fed to ruminant animals. In fact, low quality/high fiber forages can be improved significantly by the AFEXTM process. Corn stover, switchgrass and wheat straw are considered to be poor quality forages and potential biomass feedstocks for biofuels. The AFEXTM process increased digestibility by 52, 128 and 63 percent respectively (Bals et al, 2010). Data for four other forages are listed in table 1.

Table 1. Neutral detergent fiber (NDF) digestibility after 48 hour in vitro fermentation of selected forages.


Digested (g NDF/kg biomass)

Untreated b


% Increase c

Corn Silage




Alfalfa Hay




Orchardgrass Hay




Corn Stover




Alamo Switchgrass a




Wheat Straw








a late harvest
b untreated samples prior to testing
c percent increase in treated sample over untreated sample

Alfalfa hay is typically very high quality and digestibility and did not respond to AFEXTM treatment. Miscanthus had a large percentage increase in digestibility, but is still too low to be considered as a livestock feed at this time. The biggest benefit was observed on crops that are mature when harvested.

The results of this study are important to both industries – livestock and biofuels. The livestock industry needs additional low cost forages. Many of the key potential biofuel crops, if AFEXTM treated, can be used as livestock feed. This secondary market could fill the gap and help address the “chicken and egg” issue being faced by the second generation biofuel industry. Feeding trials are underway to evaluate AFEXTM-treated corn stover for animal performance. If the feeding trials are successful, AFEXTM treated biomass could be a new market that might entice farmers to grow and supply biomass to the livestock industry in the near term while the biofuels industry develops – hopefully a win/win.

For questions or comments, please contact Dennis Pennington at pennin34@msu.edu or 269-838-8265.


Bals, B., Murnen, H., Allen, M., Dale, B. 2010. Ammonia fiber expansion (AFEX) treatment of eleven different forages: Improvements to fiber digestibility in vitro. Animal Feed Science and Technology 155 (2010) 147–155.

Renewable Fuels Association, Historic U.S. fuel Ethanol Production, http://www.ethanolrfa.org/pages/statistics, accessed June 2, 2013.

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