MSD Manual

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Professional Version

The Ruminant Digestive System


Johann (Hans) F. Coetzee

, BVSc, CertCHP, PhD, DACVCP, Iowa State University

Last review/revision Mar 2015 | Modified Nov 2022

Other than the forestomachs (rumen, reticulum, omasum), the components of the ruminant GI tract are similar to those of monogastric mammals, and the use of pharmacologic agents to treat diseases of the glandular stomach (abomasum) and intestine follows principles common to both monogastric and ruminant species. Ruminants differ significantly from other mammals in that much of their feed undergoes microbial predigestion in the forestomachs, chiefly in the rumen and reticulum. There is also postgastric fermentation in the cecum and colon, but this is much less important than in some other herbivores, eg, horses.

Ruminoreticular motility or fermentation is depressed in many conditions, including improper feeding (overload or deficiency of specific nutrients), lack of water, infectious diseases, intoxications, lesions of any part of the upper GI tract, metabolic states (eg, hypocalcemia), or reduced flow of alkaline saliva that allows pH to fall and the microbial population to be altered to an extent that is harmful to the animal. (Also see Diseases of the Ruminant Forestomach Diseases of the Ruminant Forestomach et seq.)

The primary objectives of pharmacotherapy are to remove the cause and to promote the return of normal digestive function by meeting or reestablishing the requirements for optimal ruminoreticular function as quickly as possible. This may include any of the following: 1) ensuring an appropriate substrate for microbial fermentation; 2) providing any cofactors (eg, phosphorus, sulfur) necessary for microbial fermentative processes; 3) removing any soluble end-products, undigested solid residues, and gas; 4) maintaining continual flow culture of ruminal microorganisms; 5) ensuring that the contents of the ruminoreticulum are fluid; 6) maintaining optimal intraruminal pH (generally between 6 and 7); and 7) promoting active ruminoreticular activity.

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