Cecal Digestors
Function
Ruminants
Ability to efficiently digest and extract energy from cellulose
Yes
Yes
Ability to utilize dietary hexose sources directly
No
Yes
Ability to utilize the protein from fermentative microbes Yes
No
Both ruminants and cecal digesters are very successful. Each of these two strategies has what you might call strengths and weaknesses relative to the other, which predispose these groups of animals to distinctive diseases, as will be explored in subsequent sections . Fermentation is supported by a rich and dense collection of microbes. Each milliliter of rumen content contains roughly 10 to 50 billion bacteria , 1 million protozoa and variable numbers of yeasts and fungi. The distribution of microbial species varies with diet. Some of this appears to reflect substrate availability; for example, populations of cellulolytic bugs are depressed in animals fed diets rich in grain.
The Products of Fermentation
Fermentation occurs under anaerobic conditions. As a consequence, sugars are metabolized predominantly to volatile fatty acids (VFAs). Additional major products include lactic acid, carbon dioxide and methane. The principle VFAs are acetic, proprionic and butyric acids, which collectively provide for the majority of an herbivore's energy needs . The ratio of these VFA's vary with diet, although the major product is always acetate. On a diet high in fiber, the ratio of acetic to proprionic to butyric acids is roughly 70:20:10. These small lipids are used for many purposes, but the paramount importance of VFAs to herbivores is that they are absorbed and serve as the animal's major fuel for energy production, serving much the same function that glucose does in you.
The three major VFA's absorbed from the rumen have somewhat distinctive metabolic fates:
Acetic acid is utilized minimally in the liver and is oxidized throughout most of the body to generate ATP. Another important use of acetate is as the major source of acetyl CoA for synthesis of lipids.
375
Made with FlippingBook Publishing Software