1.1 Enteric Fermentation
1.2 Manure Management Facilities
This section identifies indicators of situations in which methane emissions are relatively high per unit product produced. The choice of developing indicators of emissions per unit product, as contrasted with indicators of total emissions, is based on two main considerations.
· Demand Driven. The practice of maintaining livestock is primarily driven by the demand for livestock products, including: milk, meat, work (i.e., draft power), and hides.1 By focusing on emissions per unit product produced, the indicators identify those conditions under which emissions are high relative to the demand for livestock products that is being satisfied.1 It should be noted that in some economic systems livestock are kept principally as a means of storing wealth, without consideration of their productive value. This aspect of livestock management, although important in selected areas, is not a dominant feature of livestock production globally.· Mitigation Potential. The situations with high emissions per unit of product represent those conditions under which emissions reductions can most likely be achieved without sacrificing overall production. By reducing emissions per unit of product produced, production levels can be maintained (or increased) while methane emissions are reduced.
Enteric fermentation refers to the fermentation of feed as part of the normal digestive processes of livestock. In ruminant animals (principally cattle, buffalo, sheep, and goats), a significant amount of fermentation takes place in the rumen, resulting in relatively large methane emissions per unit of feed energy consumed. Pseudo-ruminant animals (e.g., horses) and monogastric animals (e.g., pigs) do not support the same level of feed fermentation, and consequently emissions from these animals are relatively low. Therefore, indicators of methane emissions from enteric fermentation focus primarily on ruminant animals.
Ruminant animals with low levels of production efficiency have relatively high methane emissions per unit of product. This situation results because these animals use a large fraction of their feed intake solely for maintenance (i.e., for the basic metabolic processes required to stay alive). Methane emissions associated with this maintenance feed intake are spread over a relatively small level of production, resulting in a high level of emissions per unit product. In animals with higher levels of production efficiency, the maintenance emissions are spread out over a larger amount of production, thereby reducing methane emissions per unit product (although emissions per individual animal may be higher). Key indicators of those situations with high methane emissions per unit of product are primarily socio-economic in nature, including the following:
· Productivity levels of animal production. Low productivity indicates high levels of methane emissions per unit product. Productivity is measured in terms of: offtake rates (e.g., kilograms of meat produced per mature cow per year, kilograms of milk produced per mature cow per year); animal growth rates; and feed conversion efficiency (i.e., total kilograms of feed required to produce a kilogram of product).In addition to these indicators of production efficiency, feed quality also has an impact on methane emissions, although it is less significant than production efficiency. Very low quality feeds, such as untreated rice straw or poor rangelands in arid areas, tend to lead to higher emissions per unit of feed intake in ruminant animals. Low levels of feed digestibility (e.g., below 55 percent) or low levels of metabolizable energy content in the feed are often indicators of higher methane emissions per unit of product.
· Marketing channels. The absence of adequate marketing channels for livestock products tends to limit improvements in production efficiency. Such channels, including the ability to transport and process products and receive reliable prices, are needed so that individual producers can receive the benefits of improved levels of production that are associated with improved production efficiency. In many regions, marketing cooperatives are the principal institutions that develop and maintain marketing channels, and hence the absence of effective cooperatives is often an indicator that adequate channels do not exist.
Manure from all types of livestock can produce methane. In order to emit high levels of methane per unit of product produced, the manure must be managed under anaerobic conditions (i.e., in the absence of oxygen). Only facilities that manage manure as a liquid or slurry are capable of sustaining anaerobic conditions. These facilities include lagoons, pits, and tanks. Manure that is handled in dry form, spread on fields, dried for fuel, or deposited by grazing animals does not produce an appreciable amount of methane.
Liquid manure management facilities are most commonly used when there is a large concentration of animals at a single facility, such as at a large dairy or pig farm. Consequently, the most effective indicator for the presence of liquid manure management facilities is the average herd size, i.e., the average number of dairy cows or pigs per farm in a region. Because liquid systems (and large farms in general) require a certain amount of mechanization to be workable, such systems are generally not found in rural areas of developing countries. Instead, in developing countries such facilities are often located near urban areas where product demand is high and transportation of product can be minimized. Consequently, it is appropriate to focus attention on large peri-urban facilities as potential sources of manure methane.