Editor's note: This article was written by Alexander Hristov, associate professor of nutrition, Penn State Department of Dairy and Animal Science and first appeared in the Penn State Dairy Digest.
In relation to our research at Penn State, I’m being asked now and then to give my opinion about domestic ruminants greenhouse gas (GHG) emissions. The last one was a piece for Penn State’s Live (March 3rd, 2011; Probing Question: Are cow burps contributing to global warming?). Soon after that, I received an e-mail from a Penn State alumnus raising the question of the historical wild ruminants’ contribution to GHG in North America. This gentleman had been unsuccessfully trying to get an answer to his question through contacting various Penn State’s Departments and even EPA. I thought this was an intriguing (and important) issue worth researching.
In North America, there are many native ruminants, i.e. herbivore animals with a complex digestive system, a major compartment of which is the rumen. Some present-day examples are the bison (Bison bison), the elk (or wapiti, Cervus Canadensis), or the deer (white-tailed, Odocoileus virginianus or mule, Odocoileus hemionus). The common feature of all ruminants is the microbial fermentation and degradation of fibrous feeds occurring in their forestomachs, primarily the reticulorumen (i.e., the joint compartments of the rumen and the reticulum). The results of this fermentative process are products benefiting the host animal (microbial protein, used by the animal as a source of amino acids and volatile fatty acids, used as an energy source).
Rumen microbes, on the other hand, thrive in the “temperature-controlled”, oxygen-free (the typical rumen microbes are anaerobes), substrate-rich environment that the host animal provides for them. Indeed, this symbiotic process is one of Nature’s wonders and has allowed ruminants to dominate the natural world. Ruminal fermentation, however, is not a very efficient process (at least from a biochemical point of view) and results in several by-products considered a waste, mainly carbon dioxide and methane. Methane is a potent GHG and domestic ruminants have been blamed by many for a large portion of the global GHG emissions, thus having a significant impact on climate change. The importance, or rather unimportance, of livestock to global GHG emissions has been discussed by us and by others (see, for example, Hristov, 2008); here, we’ll focus on wild ruminants.