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DIGESTION IN THE RUMINANT
Author(s) -
MCANALLY R. A.,
PHILLIPSON A. T.
Publication year - 1944
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1944.tb00301.x
Subject(s) - rumen , ruminant , digestion (alchemy) , fermentation , cellulose , starch , food science , carbon dioxide , chemistry , biology , xylose , zoology , biochemistry , agronomy , ecology , chromatography , crop
Summary 1. The diet of ruminants is peculiar in that it contains large quantities of cellulose and other carbohydrates which are indigestible except by the aid of bacteria; it is probable that the numerous protozoa of the rumen do not play a vital part in digestion. 2. Food passes to the fermentation chamber formed by the reticulum and rumen where it is kept in continual motion by rhythmic contractions of this organ. Regurgitation is caused by an inspiratory effort with a closed glottis; the bolus after being remasticated returns to the fermentation chamber. 3. Passage of ingesta from the rumen is slow and spread out over a period of days. Digestion is more efficient in the ruminant than in the horse and pig owing to the greater time spent by the food in its alimentary tract rather than owing to the act of remastication. 4. The voluminous secretion of saliva is responsible for the maintenance of a moisture content and reaction of the ingesta of the rumen suitable for the bacterial fermentation of carbohydrate. The conditions are anaerobic, since carbon dioxide and methane are the chief gases present, oxygen being found only in traces, if at all. 5. The breakdown of cellulose and other carbohydrates is accomplished mainly by bacteria, though plant enzymes may play a minor part. The products of this fermentation are largely carbon dioxide, methane and the volatile fatty acids, though it has been suggested that a starch‐like polysaccharide is synthesized. The degree of digestion of cellulose is affected by the other constituents of the diet. 6. The rate and degree of digestion observed by the use of an indigestible constituent of the food as an index show that the total digestion and in particular that of cellulose in the rumen is considerable within 14 hr.; this is supported by measurements of the rate of evolution of methane. 7. Absorption of the volatile fatty acids and of certain drugs has been proved to occur from the rumen. 8. Fermentation is not confined to the rumen; it also occurs in the caecum of the ruminant. The authors are greatly indebted to Sir Joseph Barcroft, F.R.S., for his constructive criticism and help in the preparation of the manuscript.