14 Utilization of Cellulose by Ruminants B. R. B A U M G A R D T
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Department of Animal Science, Pennsylvania State University, University Park, Pa.
Expressed in an oversimplified manner, this part of the Symposium on Cellulases and Their Applications w i l l deal with the utilization of lignocelluloses in the production of human food using ruminant animals as intermediates. Many arguments have been advanced for the relative merits of animal vs. plant agriculture in the production of food for man. Thorough consideration indicates that when properly used and integrated, these two forms of food production can be complementary rather than competitive. Livestock offer a way of utilizing land resources that cannot be used directly to produce human food; they can utilize waste products of the food industry, and many other industries, and they can, i n the case of ruminants, synthesize proteins and vitamins, and release energy from low grade raw materials including cellulose and urea. Ruminants include those animals that we normally think of as cudchewing, or ruminating animals; common examples include cattle, sheep, and goats. The most unusual feature of these animals involves their digestive system, and in particular their multi-compartmented stomach. They are commonly referred to as having four stomachs. The true stomach, that part comparable to the stomach of man, is preceded by 3 other compartments. These are, in order, the rumen, reticulum, omasum, and abomasum. When food is swallowed by a ruminant it first enters the Rumen and reticulum which are not well separated. This rumeno-reticulum is by far the largest part of the ruminant stomach, having 80-85% of the total stomach capacity. N o digestive enzymes are secreted by the animal into the rumeno-reticulum, but this large organ, retaining a high moisture content, maintains a large bacterial and protozoal population under near anaerobic conditions, and functions as a fermentation vat. A large and strong musculature keeps the contents agitated and the animal secretes large quantities of alkaline saliva, perhaps 10 liter/day in a sheep and 85-100 liter/day in a cow, which helps neutralize the short-chain organic acids produced from the microbial fermentation. p H in rumen w i l l range 242
In Cellulases and Their Applications; Hajny, G., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.
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14.
BAUMGARDT
Utilization of Cellulose by Ruminants
Figure 1.
243
Digestive system of the cow
from 5 to 7 (depending upon diet and time after feeding) and the temperature is about 39°C. The main features of the rumen phase of digestion include: (1) Fermentation of dietary sugars, starches and cellulose to produce volatile fatty acids, principally acetic, propionic, and butyric acids, which are absorbed and used by the host animal for energy and various synthetic functions. (2) Synthesis of microbial protein from protein and non-protein nitrogen in the diet. The microbial protein is later digested and the amino acids used by the host. (3) Synthesis of the B-vitamins and vitamin K .
In Cellulases and Their Applications; Hajny, G., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.
244
CELLULASES A N D THEIR APPLICATIONS
Two points should be mentioned in relation to this part of the symposium.
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(1) To maintain normal rumen function and physiological activity some tactile or scratch stimuli must be provided i n the rumen. This is normally provided by the "fibrousness" of roughage and fodder crops. (2) Although cellulase activity of rumen microflora is high, lignocellulose feed stuffs are only partially degraded; that is, only part of the potential energy is made available for animal production. Thus, we w i l l be dealing with what might appear to be two divergent uses of lignocellulose in ruminant feeding. One concerns the use of lignocellulose as a roughage substitute to provide the tactile stimulation necessary for rumen function, without particular regard to any nutritive contribution from the lignocellulose per se. Such possibilities find use in cattle feed-lot operations where grain feeding is practiced to produce high quality beef rapidly. The other aspect concerns modifications of lignocellulosic materials to provide new energy sources for ruminants, so that grains might be conserved for direct consumption by man. These two needs, or aspects of the problem, are now separated largely on the basis of geography and agricultural productivity, but time may well dictate that obtaining new energy sources is the more critical and fundamental problem.
In Cellulases and Their Applications; Hajny, G., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.
