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Continuous In Vitro Culture System for Ruminant Research II. Biological Characterization^1,2,

University of Illinois, Urbana⁴

Abstract

A continuous in vitro culture system was characterized over 21 days to evaluate its mechanical reliability, normal operating characteristics and simulation of in vivo conditions.

Average pH, percent dry matter and cellulose disappearances were 6.44, 39.1 and 41.7, respectively. These criteria were quite stable and dry matter and cellulose disappearances were acceptable considering a theoretical 16.9-hr. fermentation period.

Acetate, propionate, butyrate, isovalerate, valerate and total acid concentrations averaged 52.7, 42.5, 11.9, 4.8 and 112.6 mcmoles/ ml, respectively. Little change occurred in any acid concentration except propionate, which increased sharply from day 0 to day 3. A total acid production rate of 0.67 mmoles/hr./ 100 ml of culture was comparable to other systems but slightly lower than in vivo production rates.

Ammonia concentration averaged 6.26 mgm NH₃—N/100 ml and was relatively stable. Calculations indicated that approximately 19 mgm NH₃—N/100 ml were utilized for microbial metabolism.

DNA dropped sharply from 335.46 mcg/ml initially to 1.14 on day 2 and increased to approximately 70 mcg/ml on day 3 and averaged 70.9 mcg/ml.

The complex protozoa population of approximately 1.4 x 10⁶/ml initially, decreased rapidly to a simple population of approximately 2 x 10³/ml. Holotrich protozoa disappeared about day 5. Microscopic bacterial counts decreased from 12.5 x 10⁹/ml initially to 8 x 10⁹/ml by day 3.

Correlations between DNA and total acid production, microscopic counts of bacteria and protozoa and percent dry matter and cellulose disappearances were calculated and discussed.

A gas diffusion study indicated that the polyethylene collection bottles and plexiglass fermentors gained 5.9% and 15.7%, respectively, oxygen over 14 days. Plexiglass appeared to be a suitable material for fermentation chambers but was a poor choice for an anaerobic fermentation chamber because of its apparent permeability to oxygen.

¹ Data taken from thesis submitted by the senior author to the Graduate College, University of Illinois, in partial fulfillment of the requirements for the Ph.D. degree.

² Supported in part by federal funds (Hatch 20–346 and 20–348) and by a grant-in-aid from Dow Chemical Company, Midland, Michigan.

³ Present address: Department of Meat and Animal Science, University of Wisconsin, Madison.

⁴ Animal Science Department.