Modifiers of rumen fermentation

Rumen fermentation processes are usually kept within narrow bounds and, as they form an integrated system, any changes made have more than one outcome. Thus, modification of the processes to one desired target is difficult. Nevertheless, there are products that are used to modify the fermentation to achieve specific results (see also Chapter 8). 

The use of antibiotics and probiotics was discussed above. Other rumen modifiers include buffers, methane inhibitors and bloat-preventing substances. 

Antibiotics such as virginiamycin and monensin have been used to select against bacteria that produce lactic acid. Certain probiotics encourage the uptake of lactic acid (see above). 

The production of methane in the rumen is a wasteful process (up to 10 per cent of the gross energy) and contributes to the earth s greenhouse gases.The use of additives to suppress methane production is discussed in Chapter 8 (see p. 188). 

Under normal conditions, rumen fermentation produces gases that, by the action of ruminal and reticular contractions, accumulate in the area known as the cardia, from which they are passed up the oesophagus in the process of emctation. Bloat occm if the gas becomes trapped and the animal is not able to clear it. Rumen stasis due to acidosis is one of the causes of free gas bloat, but on certain pastures, particularly those rich in legumes, and on high-concentrate (feedlot) diets, the fermentation process in the rumen can result in rumen gases being trapped within fluid bubbles. Therefore, the gas cannot be eructated as normal and pressure builds up in the rumen. The condition is known as 

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