Cud 1028429 218117081 2008-06-09T06:22:57Z Aleenf1 818523 Reverted edits by [[Special:Contributions/24.14.17.69|24.14.17.69]] ([[User talk:24.14.17.69|talk]]) to last version by Winterspan :''CUD is an acronym sometimes used to describe the genetic disorder [[Primary carnitine deficiency]]. See also [[Cud (band)]].'' '''Cud''' is a portion of food that returns from a [[ruminant]]'s stomach in the mouth to be chewed for the second time. More accurately, it is a [[Bolus (digestion)|bolus]] of semi-degraded food [[regurgitation (digestion)|regurgitated]] from the [[reticulorumen]] of a [[ruminant]]. Cud is produced during the physical digestive process of [[rumination]], or "chewing the cud". The idiomatic expression ''chewing one's cud'' means ''meditating'' or ''pondering''. == Explanation == The [[alimentary canal]] of ruminants, such as the [[cow]], [[goat]], [[sheep]] and [[antelope]], is unable to produce the [[enzymes]] required to break down the [[cellulose]] and [[hemicellulose]] of plant matter. Accordingly, these animals have developed a [[symbiotic]] relationship with a wide range of [[microbes]], which largely reside in the reticulorumen, and which are able to synthesize the requisite enzymes. The reticulorumen thus hosts a microbial fermentation which yields products (mainly [[volatile fatty acids]] and microbial protein), which the ruminant is able to digest and absorb. == Process of rumination == The process of rumination is stimulated by the presence of [[roughage]] in the upper part of the reticulorumen. The chest cavity is stretched, forming a vacuum in the gullet that sucks the semi-liquid stomach content into the [[esophagus]]. From the esophagus it is taken back to the mouth with retro [[peristalsis|peristaltic]] movements. When the stomach content, or the cud, arrives in the mouth of the ruminant, it is pushed against the palate with the tongue to remove excess liquid, the latter is swallowed and the solid material is chewed thoroughly. The function of rumination is that food is physically refined to expose more surface area for bacterial working in the reticulorumen, as well as stimulation of [[saliva]] secretion to [[Buffer solution|buffer]] the rumen [[pH]]. == Chemistry == The reticulorumen has an optimum pH of 6.5 for the microbe population to live and function. Consumption by ruminants of an insufficiently fibrous diet leads to little cud formation and therefore lowered amounts of saliva production. This in turn is associated with rumen [[acidosis]], where the rumen pH can fall to as low as pH 5 or lower. Rumen acidosis is associated with a lowered appetite which leads to still lower rates of saliva secretion. Eventually, a collapse of the microbial [[ecosystem]] in the rumen will occur because of the low pH. Acute rumen acidosis can lead to death of the animal, and will occur if the animal is allowed to eat a diet with no roughage but high levels of highly [[digestible]] starchy concentrate. It is thought that most dairy cows in intensive systems of milk production have sub-acute acidosis because of the high rates of cereals in their diets relative to an insufficient amount of forage. {{Fact|date=March 2007}} == Final digestion == When food has been degraded efficiently it passes from the reticulorumen through the [[reticulo-omasal orifice]] to the [[omasum]] followed by the [[abomasum]] to continue the digestion process in the lower parts of the alimentary canal. No enzymes are secreted in the rumen. Enzymes and [[hydrochloric acid]] are only secreted from the [[Abomasum]] (fourth stomach) onwards, and ruminants function from that point onwards much like monogastric animals, such as pigs and humans. [[Category:Digestive system]] [[lt:Atrajojimas]] [[no:Drøvtygging]]