Enteric methane from ruminants accounts for about 11-17% of methane generated globally, or 17-30% of methane from human activity. Methane arises from the activity of methanogens in the rumen that use hydrogen to reduce carbon dioxide, thereby preventing the accumulation of reducing equivalents, which would otherwise impede ruminal fermentation. Although this process is desirable from a fermentation perspective, it is energetically costly, as cattle emit 2-12% of their gross energy intake in this potent greenhouse gas (GHG). Many production practices aimed at increasing efficiency of production, such as including grain and ionophores in diets, also lower methane emissions. These practices were adopted long before issues arose over the role of methane from livestock in climate change. Dietary inclusion of free oils or oil-rich feeds (e.g. oilseeds, distillers' grains and micro-algae), biologically active plant compounds (e.g. condensed tannins, saponins and essential oils), rumen fermentation modifiers (e.g. yeast and bacterial direct-fed microbials), as well as improvements in forage quality may allow for further reductions in methane emissions from cattle. The optimum dietary strategy will depend on the particular farm, its geographic location, the feedstuffs available and the type of animals being fed. Reductions can occur as decreased methane output per animal per day or as decreased methane output per kg of meat or milk produced, but ultimately, it seems prudent that mitigation practices be assessed on the basis of the extent to which they reduce methane emissions per kg of meat or milk produced. Furthermore, potential mitigation practices need to be assessed from the perspective of the entire life cycle, as a reduction in GHG in one sector of the production cycle can often lead to changes in GHG emissions in another sector.

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Canadian beef consumption is approximately 31 kg per annum, or a third of all meats consumed. Beef is a nutrient-rich food, providing good quality protein, vitamins B-6 and B-12, niacin, iron, and zinc. However, animal fats have gained the reputation of being less healthy. The identification of the anticarcinogenic effects of beef extracts due to the presence of conjugated linoleic acid (CLA) has heightened interest in increasing the amount of CLA deposited in beef. Beef cattle produce CLA and deposit these compounds in the meat; thus, beef consumers can receive bioformed CLA. Beef contains both of the bioactive CLA isomers, namely, cis-9, trans-11 and trans-10, cis-12. The relative content of these CLA isomers in beef depends on the feeds consumed by the animals during production. Feeding cattle linoleic acid-rich oils for extended periods of time increases the CLA content of beef. Depending on the type and relative maturity of the pasture, beef from pasture-fed cattle may have a higher CLA content than beef from grain- or silage-fed cattle. In feedlot animals fed high-grain diets, inclusion of dietary oil along with hay during both the growth and finishing phases led to an increase in CLA content from 2.8 to 14 mg/g beef fat, which would provide 77 mg CLA in an 85-g serving of beef. The CLAs appear to be concentrated in intramuscular and subcutaneous fat of beef cattle, with the CLA trans-10, cis-12 isomer being greater in the subcutaneous fat.