Species characters are given for two specific situations:

- Feeding characteristics of livestock species and potential impact on the environment, and
- Feed digestion characteristics of livestock species and related methane emission and quality of excreta

Feed Digestion Characteristics

The matrix presents some principal feed digestion characteristics, related methane emissions and quality of excreta by species.

Specific digestion or pre-digestion abilities refer to the anatomy, activities and physiology of the animals in relation with the digestion of feed.

Methane (CH4) production refers to the methane produced during digestion of the feed and the potential production afterwards in the faeces. The relevance is that CH4 is assumed to contribute 24 times more to global warming than CO2. Whether carbo-hydrates, including biodegradable fibres as such as cellulose and hemi-cellulose, are decomposed in or outside the animal, it will always result in a combination of CO2 and CH4. Under aerobic (O2) conditions more CO2 is produced and under anaerobic conditions more CH4 is produced. When decomposition is through burning then only CO2 is produced.

A constraint to the reduction of CH4 emissions by ruminants and equines is that a substantial quantity of CH4 is produced in the digestive tract and expelled by the animal. It has been suggested that feed with a lower fibre content and a high digestibility could reduce the CH4 production by ruminants and equines. However, whilst this is true on an individual basis, it is questionable whether this is significant on a global scale. Increases in production of feed with a low fibre content in general result in a greater increase in by-products and crop residues with a high fibre content. These residues are often feed for ruminants, or if not, partly decompose under anaerobic conditions. In the carbon cycle CH4 is still being produced, spread over different production systems. For the overall impact on global warming, however, this does not make a difference.

In case of pigs and poultry the decomposition of most of the fibres takes place after digestion, in the manure. The amount of CH4 produced will thus depend on the outside circumstances: if aerobic little CH4 produced, if anaerobic much CH4. The advantage of pig and poultry is that more of the CH4, if produced, can be captured, i.e. in bio-gas installations. It can then serve as fuel and is converted into CO2.

Urine contains water-soluble residues from physiological processes. In the context of this table, only N (nitrogen from urea and uric acids) and K (in potassium salts) are mentioned.

Faeces are composed of undigested feed, residues from digestion fluids and the digestive tract. It contains N (nitrogen), P (phosphorus), K (potassium), other (micro) minerals and vitamins from feed residues and the digestive tract. A high bacterial content enables further decomposition of the faeces under (an-) aerobic conditions. The dry matter content (DM) of faeces is species specific but can vary considerable within species depending on health status of the animal and type of feed consumed.
The amount of dry matter produced is, by definition, equal to the amount of dry matter consumed times the digestibility. The digestibility of a feed is about the same for ruminants, but can vary for other, non-ruminant species. Part of the dry matter in the faeces is in the form of structural organic matter (SOM): lignin and other un-digested fibres that decompose only very slowly after being excreted. The organic matter in the soil, important for soil structure and soil biodiversity, is mainly composed of SOM.

Manure use refers to the potential use of manure as source for energy, as feed and as fertiliser.

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