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Studies on the in Vitro Digestion of Cellulose By STUDIES ON THE IN VITRO DIGESTION OF CELLULOSE BY RUIvIEN MICROORGANISMS By ROBERT LAWRENCE SALSBURY A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Dairy 1955 ProQuest Number: 10008419 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10008419 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 STUDIES ON THE IN VITRO DIGESTION OF CELLULOSE BY RUMEN MICROORGANISMS By ROBERT LAURENCE SALSBURY rjmiirr AN ABSTRACT Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Dairy Year 1955 Approved 1 Four methods of incubating rumen fluid for the purpose of studying cellulose digestion in vitro were examined. Under the conditions used, it was found that the maximum cellulose digestion and most reproducible results were obtained when a semipermeable sac was used and the inoculum: mineral-solution ratio was small. When CC>2 was passed through the fer­ mentation mixture during incubation, the percentage cellulose digested was slightly lower than when CO2 was used very briefly at the start of the fermentation period. A modification of the "artificial saliva" of McDougall (194#) was adopted as a source of mineral nutrients. Cellulose digestion was increased by addition of urea up to 0.1% when no readily available carbohydrate was added but decreased by addi­ tions of 0.15 or 0.20%. Addition of glucose up to 0.2% did not appreci­ ably affect the amount of cellulose digested. Addition of large amounts of cobalt (up to 200 ppm.) depressed cellulose digestion, the amount of depression being greater as the con­ centration of the cobalt increased. Addition of vitamin B^2 (up to 50 micrograms per liter) had no appreciable effect on cellulose digestion. Inocula obtained from a steer receiving high levels of cobalt had a decreased ability to digest the cellulose in a wood cellulose , alfalfa leaf meal and timothy hay when incubated without the addition of urea. Yrhen urea was added before incubation the inocula had a decreased ability to digest the cellulose in the wood cellulose and timothy hay but the digestion of the cellulose in alfalfa leaf meal was essentially unchanged. A comparison of rates of cellulose digestion in vitro showed that 2 the cellulose in alfalfa leaf meal was digested at a relative iy greater rate than the wood cellulose or the cellulose of cotton linters when compared on the basis of percentage of 24-hour digestion. ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to Dr. C. F. Huffman, Department of Dairying, Dr. C. K. Smith, Department of Microbiology and Public Health, and Professor C. 17. Duncan, Department of Agricultural Chemistry for their interest and timely suggestions throughout this investigation and for their assistance in the prepara­ tion of this manuscript. Gratitude is also expressed to Dr. G. M. Ward and R. S. Emery, Department of Dairying for their interest and assistance. The writer is indebted to the Institute of Nutrition, Michigan State College and to Dr. L. A. Moore, Agricultural Research Service, U. S. D. A., for financial assistance during this investigation. The writer also wishes to express his grateful appreciation to his wife for her considerable assistance and encouragement throughout this study. TABLE OF CONTENTS Page INTRODUCTION ..................................................... 1 REVIEW OF THE LITERATURE ........................................ 3 Fermentation Methods ..................................... 3 Methods for the Determination of Cellulose ............... 5 Digestion of Cellulose by the Ruminant .................. 8 Mechanism of cellulose breakdown ...................... 8 Amount of cellulose digested in the rumen ............ 17 Rate of cellulose digestion in the r u m e n ............... 20 Effect of dry matter concentration on cellulose digestion 21 Effect of soluble carbohydrate on cellulose digestion . 22 Effect of nitrogen source on cellulose digestion . 23 Other factors affecting cellulose digestion .... 25 EXPERIMENTAL P A R T .............................................. 28 SECTION I - PRELIMINARY EXPERIMENTS . 28 EXPERIMENTAL ................................................. 28 Animals u s e d ........................................... 28 Collection of samples .................................. 28 Fermentation procedures ............................... 29 Determination of cellulose ............................ 30 RESULTS . 30 SECTION II - EXAMINATION OF THE M E T H O D S ...................... 47 EXPERIMENTAL ................................................. 43 Fermentation procedures ............................... 48 Determination of cellulose ............................ 51 RESULTS .................................................... 52 Determination of cellulose ............................ 52 Effect of cysteine-HC1 and sodium thioglycollate with Complex No. 2 .... 56 Effect of different mineral solutions ............... 59 Page Effect of rate of passage of CO2 ..................... 62 Effect of manner of introduction of CO2 ............... 6/+ Effect of increasinp- the calcium content of Complex No. 2 66 Fermentation without a s a c ............................ 66 Effect of ratio of inoculum to mineral solution . 6.9 SECTION III - FACTORS AFFECTING CELLULOSE DIGESTION.... 73 EXPERIMENTAL ........................................... 73 Fermentation procedure ............................... 73 Determination of cellulose ............................ 76 RESULTS .................................................... 77 Effect of 2,4-D on cellulose digestion ............... 77 Effect of certain treatments on digestion of cellulose of corn f i b e r ........................................ 79 Difference in digestion of the cellulose of different substrates ........................................ 81 Effect of urea concentration on cellulose digestion . 81 Effect of glucose concentration on cellulose digestion . 84 Effect of cobalt and vitamin B12 on cellulose digestion 86 Rate of cellulose digestion............................ 94 Cellulase activity ..................................... 100 Comparison of in vitro with in vivo cellulose digestion 103 DISCUSSION........................................................... 104 Determination of Cellulose 104 The Fermentation Methods ....... 106 Examination of the Fermentation Methods Used ............ 108 Factors Affecting Cellulose Digestion In Vitro ............ 112 Effect of 2,4-D ........................................... 112 Effect of alkali treatment of corn fiber ............. 113 Effect of urea c o n c e n t r a t i o n ............................113 Effect of glucose concentration ...................... 113 Effect of added cobalt or vitamin B] _ 2 ....................H 4 Rates of Cellulose Digestion......................... 115 Comparison of In Vitro with In V ivo Cellulose Digestion . 119 Page SUMMARY ............ .... ... 128 LITERATURE CITED ..................................... 122 APPENDIX ........................................................... 131 INTRODUCTION The digestive tract of the ruminant is uniquely adapted to the digestion of fibrous plant material. The key to the ruminant’s ability to digest material which is unavailable to monogastric animals is its possession of a fore-stomach or reticulo-rumen. This organ functions as a large fermentation vat in which a more or less stable microbial popu­ lation attacks ingested food. Products of the microbial action become available to the animal and in passing along the digestive tract many of the microorganisms themselves are digested by the enzymes of the animal. Consequently, constituents of the feed which would otherwise not be util­ ized by the animal are made available to it. One such constituent is cellulose. The importance of understanding the mechanism of the digestion of cellulose and other materials in the rumen now becomes obvious. Not only should such an understanding be of great value in choosing the most suit­ able ration, but it could lead to the modification of some of the proces­ ses to permit more efficient utilization of feed. The use of fistulated animals has helped considerably in the study of rumen processes. In vivo studies, however, have been complicated by the fact that the investigator has to deal with a dynamic system. There is the frequent -passage of material out of the reticulo-rumen into the omasum, the loss of some constituents through the rumen wall, and unless feeding is carefully controlled, the intermittent introduction of feed, water, and saliva. There has been a tendency in recent years to use in vitro methods in the study of rumen microorganisms. This avoids the complications mentioned above but introduces others, notably the lack of assurance that the
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