|Fig. 1: sheep fitted with mechanisms for collecting exhaled methane. (Source: Wikimedia Commons)|
In the quest to find new energy sources or conserve the ones we already have, the focus is usually on industrial processes; reliable chemical and physical processes that are repeatable. In power generation the focus is on photovoltaics, nuclear power, hydropower generation or storage, and other build-to-suit solutions. Power conservation focuses on insulation to conserve thermal energy, generation of increasingly direct and efficient photon generation (lately using LEDs), and more efficient engines to provide cars with more miles per gallon of fuel. There is however, a whole biological dimension of energy generation and management that can be illustrated by focus on our most common source of meat and dairy products--the cow.
Given the large numbers of cows on the planet which are maintained for dairy and meat production, any energy conservation or energy production that is enhanced by taking a whole-cow-istic approach can be multiplied by the hundreds of millions of cows in the world today.
Cows are better at converting grass into energy than people are, but they still leave lots of the potential energy of their food unharvested. Collectively, cow manure alone can yield between one third and one ninth of energy that is generated from world coal consumption, depending on how the manure is processed. If processed into methane it could replace one-fifth of the world's supply of natural gas. 
A long-established method of generating methane and power from cows is through the use of manure digesters. For some capital investment in equipment and small net operational expense, a farm can profit from processing its manure in a digester system to generate methane, which can be used to generate electricity. Some of the methane can also be used to provide heat, as well as electrical pump power, required to keep the digestion process going. One case study at the Top Deck Holstein farm found a simple return rate of 8% on investment, using a manure digester and a microturbine for power generation. Using remains from the digested manure as a cow bedding substitute could potentially raise the simple annual return rate to 11.5%.  Tantalizing as the economic resource of methane from manure is, there is a much greater potential methane energy source going to waste. Only 10% of cow methane comes from manure. 90% is originating from enteric fermentation, that is, emissions in the form of ructus and flatus. 
There are some, apparently serious, efforts to mitigate a large contributor to global warming by capturing digestive system gas emissions from cows and using the greenhouse-gas methane as an energy source. The experimental cow fanny pack apparatus for capturing the bovine-generated flatus methane can capture enough methane each day to power a car. A similar apparatus for capturing ructus from sheep is shown in Fig. 1. A proof-of-concept project by Argentina's National Institute of Agricultural Technology (Instituto Nacional de Tecnologa Agropecuaria (INTA)) inserted tubes into cows' rumens to channel gases from the cows' digestive tracts into a lightweight collection bag carried by the cow. INTA was able to collect 300 liters of methane per cow per day. 
The meat packing industry brags, with regards to hogs, that they use everything but the squeal. While that industry may also come close to using everything but the moo, back on the farm, cows are wasting a large amount of their energy intake by emitting it, relatively undigested, in the form of methane, currently regarded as an undesirable greenhouse gas. As a contributor to atmospheric warming, methane is assigned a 100-year Absolute Global Temperature Change Potential (AGTP) of 2.34 × 10-15, whereas the value for carbon dioxide is 5.47 × 10-16.  A cow can produce 250 to 500 L of methane per day. 
Reducing methane emissions from cows can have various health and legal benefits for the cows. We deal with beneficial dietary health interventions first and leave the legal aspects as an exercise for the reader. 
Methane emission reduction is reflected in the otherwise lost energy content of the methane being made available to the cow. This means less consumption of feed and the concomitant energy represented by that feed and required for its production.
There are numerous mostly dietary treatments applied to cows to reduce their methane production and increase their energy intake from their food. As with drugs and supplements for humans, additions to feed must be examined closely. Some have temporary effects or, long term, can even prove fatal to the cow.
Despite the ubiquitous nature of cows, we have yet to fully tap into their potential as a source of natural gas. Existing efforts today generally focus on processing the manure to generate methane, but there is a much greater potential methane energy source, gas emissions, which is not being utilized. Further, research must be done into the effects of reducing methane emissions from cows, but for now we can look at cows in a new light as providing more than just energy as a nutrient.
© Genevieve Payzer. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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