Acidosis, ruminants

Stimulation of lactate uptake by Selenomonas ruminatum to prevent or correct a decrease in ruminal acidosis... 

The rumen environment lowering the rumen pH from 6.7 to 5.7 has been shown to halve microbial protein production, which may be significant when diets are rich in soluble carbohydrate and low in fibre, with consequent production of lactic acid and ruminal acidosis. 

FiM also assumes a constant ruminal pH of approximately pH 6.2 and ignores the detrimental effects that low pH can have on ruminal metabolism. The system does, however, provide an estimate of whether rumen pH is likely to be altered through the calculation of a rumen stability value (RSV).The RSV of a feed is dependent on its fibre content, whether it is a concentrate or forage, and the potential acid load (PAL).The PAL content is a measure of the amoimt of acid that wUl be produced by the feed on incubation with rmnen liquor, expressed as meq/kg DM. Typically, hay will have a PAL of 800 meq/kg DM and barley 1150 meq/kg DM. The requirement for RSV is affected by cow age, milk yield and quality, and the feeding system used. For example, fourth-lactation cows fed a total mixed ration will have a lower RSV requirement than first-lactation animals fed concentrates twice daily in the parlour. If the RSV balance (RSV from diet - RSV requirement) is greater than +20, then it is assumed that no problems with acidosis should be encountered if it is below 0, then it is advised that the diet should be modified. 

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... 

Excessive ammonia released from ruminal microbial activity on urea is absorbed across the ruminal wall where it interferes with intermediary metabolism and causes metabolic acidosis. 

Acidosis Subacute ruminal acidosis (SARA) is a digestive disorder characterized by the instability of the microbial ecosystem and by fermentations that lead to lactate, butyrate, and/or propionate rather than acetate (i.e., lactic-, butyric-, and propionic- SARA). It is a major concern in cattle health and welfare. In addition to, or besides the use of, chemical buffers and ionophores, the use of probiotics as feed additives has been investigated as a strategy to balance the ruminal microbiota and fermentation, to stabilize the ruminal pH, and therefore to prevent SARA. Most of the probiotics used in this context contain yeasts (mainly 5. cerevisiae) as the main active microorganism (Desnoyers et al. 2009). Prevotella bryantii, a Gram negative bacterial species... 

Zebeli, Q. J., D. Mansmann, H. Steingass and B.N. Ametaj, 2009. Balancing diets for physically effective fiber and ruminally degradable starch A key to lower the risk of sub-acute rumen acidosis and improve productivity of dairy cattle. Livest. Sci. 127, 1-10. 

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