Increasing atmospheric concentrations of methane have led scientists to examine its
sources of origin. Ruminant livestock can produce 250 to 500 L of methane per day.
This level of production results in estimates of the contribution by cattle to global
warming that may occur in the next 50 to 100 yr to be a little less than 2%. Many
factors influence methane emissions from cattle and include the following: level of
feed intake, type of carbohydrate in the diet, feed processing, addition of lipids
or ionophores to the diet, and alterations in the ruminal microflora. Manipulation
of these factors can reduce methane emissions from cattle. Many techniques exist to
quantify methane emissions from individual or groups of animals. Enclosure techniques
are precise but require trained animals and may limit animal movement. Isotopic and
nonisotopic tracer techniques may also be used effectively. Prediction equations based
on fermentation balance or feed characteristics have been used to estimate methane
production. These equations are useful, but the assumptions and conditions that must
be met for each equation limit their ability to accurately predict methane production.
Methane production from groups of animals can be measured by mass balance, micrometeorological,
or tracer methods. These techniques can measure methane emissions from animals in
either indoor or outdoor enclosures. Use of these techniques and knowledge of the
factors that impact methane production can result in the development of mitigation
strategies to reduce methane losses by cattle. Implementation of these strategies
should result in enhanced animal productivity and decreased contributions by cattle
to the atmospheric methane budget.