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A preliminary study of cellulose digestion in the beaver (Castor canadensis). Currier, Ann Agnes 1958

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A PRELIMINARY STUDY OF CELLULOSE DIGESTION IN THE BEAVER (CASTOR CANADENSIS). by Ann Agnes Currier D.V.M., V.S., University of Toronto, 1948 A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Arts in the Department of Zoology We accept this thesis as conforming to the standard required from candidates for the Degree of Master of Arts Members of the Department of Zoology The University of British Columbia October 1958 v i i ABSTRACT An unsuccessful attempt was made to culture cellulolytic bacteria from the caecum of the beaver. The caecum is the site of cellulose digestion in this herbivorous rodent. Cellulose digestion takes place on the surface of the food particles as demonstrated by the erosion of the surface of cellulose paper in a r t i f i c i a l caeca. The rate of digestion of cellulose was measured using chromic oxide as a food marker. A variation in cellulose digestion of values from zero to 43 per cent was obtained; this variation appeared to be influenced by the health status, the diet, and perhaps the readiness with which a particular animal accepted the regimentation imposed by the experimental procedures. Cellulose unquestionably contributes to the energy available to the beaver from food material ingested. The digestible energy from cellulose appears insignificant. In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of -a- e^-y:..^ The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. Date / srs-F i i TABLE OF CONTENTS PAGE INTRODUCTION • 1 LITERATURE SURVEY A. Food habits of the beaver (Castor canadensis) 3 B. Composition and d i g e s t i b i l i t y of plant carbohydrates 20 C. Mode of digestion of plant cellulose 23 MATERIALS A. Experimental animals 27 B. Feed 27 C. Macroscopic study 28 D. Microbiological study 28 E. A r t i f i c i a l caeca 34 METHODS A. Bacteriological study 1. Housing of experimental animals (beaver) 35 2. K i l l i n g and post mortem techniques 35 3- Microbiological study of the caecum 36 4a. A r t i f i c i a l caeca, i n v i t r o study 38 b. Caeca, i n vivo study 38 B. D i g e s t i b i l i t y study 1. Housing and feeding of the beaver 40 2. Marker determination 41 3. Cellulose determination 43 4. Apparent d i g e s t i b i l i t y 43 i i i RESULTS AND DISCUSSION PAGE A. Experimental animals 45 B. Macroscopic study 46 C. Microbiological study 51 D. Artificial caeca 53 SUMMARY AND CONCLUSIONS 71 APPENDIX I 74 U 75 n i 76 17 77 V 78 LITERATURE CITED 79 i v LIST OF FIGURES FIGURE PAGE 1. Standard curve for chromic oxide 42 2. Cellulose paper recovered from a r t i f i c i a l caeca 61 3. Apparent d i g e s t i b i l i t y of cellulose for beaver 8 over a nine-day period 64 4- Apparent d i g e s t i b i l i t y of cellulose for beaver 9 over a fourteen-day period 66 5. Apparent d i g e s t i b i l i t y of cellulose for rabbit 1 over a fourteen-day period 67 6. Apparent d i g e s t i b i l i t y of cellulose for rabbit 2 over a fourteen-day period 68 7. Apparent di g e s t i b i l i t y of cellulose for mink 1 over a nine-day period 70 V LIST OF TABLES TABLE PAGE I Plant material eaten by the beaver (Castor canadensis) i n the United States and Canada 4 I I Trees cut by the beaver (Castor canadensis) i n the United States and Canada 9 I I I Trees cut by the beaver (Castor fiber) i n Russia 16 IV Some plants eaten by the beaver (Castor fiber) i n Russia (Semyonoff, 1951) 16 V Food intake of two beaver (Castor canadensis) i n captivity (O'Brien, 1938) 18 VT Percentages of protein and fiber in the dry matter of Quereus douglasi as the tree matures (Gordon et a l . , 1939) 21 VII Composition of some plants eaten by the beaver (Castor canadensis) 22 VTII Average amount of volatile fatty acid i n blood from various blood vessels of different animals, expressed in ml. N/100 a l k a l i needed to neutralize the volatile fatty acid i n 100 ml. blood (Barcroft, 1945) 25 IX Volatile fatty acids in beaver blood - m i l l i -equivalents times 10"^ per 1D0 ml/.bf; blood (Stephenson, 1956) 25 X Percentage of blood sugar i n the circulation of various animals 26 XI Composition of U.B.C. 16-57 Ration 28 XII Per cent proximate composition of Ration 16-57 28 XIII Solution 1. Dilution blank medium (Doetsch et a l . , 1952; Hungate, 1950) 29 XIV Anaerobic agar medium 1 (Doetsch et a l . , 1952; Hungate, 1950) 30 XV Anaerobic agar medium 2 (Doetsch et a l . , 1952; Hungate, 1950) 31 XVI Solution 2 31 v i TABLE PAGE XVII Solution 3 31 XVIII Anaerobic agar medium 3 (Hall, 1952) 32 XIX Anaerobic agar medium 4, modification of B.B.L. Thyoglycollate Medium (Brewers-modified) 32 XX Stock salt solution 4 33 XXI Differential sugar medium, peptone water 33 XXII Macroscopic appearance of material i n digestive tract of beaver 47 XXIII Growth characteristics of some caecal bacteria from the beaver 54 XXIV Dextrose and cellobiose reaction of some caecal bacteria from the beaver 54 XXV Carbohydrate reaction of some caecal bacteria from the beaver 54 XXVI Some results obtained using a r t i f i c i a l caeca to demonstrate cellulose digestion 57 v i i i ACKNOlLEDGEMENTS Grateful appreciation i s extended to Dr W. D. K i t t s , Department of Animal Science, for his patience, criticism, and helpful advice. Thanks are also extended to Dr I. McT. Cowan, Department of Zoology, and to Dr A. J. Wood, Department of Animal Science, for their interest throughout this study. Many thanks are extended to a l l the graduate students, and employees of the Animal Nutrition Laboratory for their assistance, ideas, and moral support throughout the entire study. Special thanks are extended to Dr E. J. Avery, Pathologist, Canada Department of Agriculture, and his entire staff for their help i n the bacteriological aspect of this study. - 1 -INTRODUCTION Many observations of the feeding habits of the beaver show this animal to be a vegetarian. The food choice varies with the time of year. The a v a i l a b i l i t y of certain food materials influences the diet as do the actual weather conditions. Like a l l herbivores the beaver i s equipped with good grinding teeth with which to break down the c e l l wall at least physically, to liberate the nutrients contained within the c e l l walls. It would be a waste of energy i f the cellulose of the c e l l walls passed through the intestinal tract with no further breakdown. Feeding studies carried out on domestic ruminants and some non-ruminants proved that up to 60 per cent of the cellulose i n the feed i s digested. These results have promoted many investigators to try to ascertain the factors involved i n the digestion of cellulose and thereby to find the most economical feed materials. There are three common methods of studying the digestion of cellulose: direct bacteriological studies with the isolation of cel l u l o l y t i c organisms; i n vi t r o studies of the contents of sections of the digestive tract of herbivores have demonstrated that the site of digestion i s the rumen of the ruminant and the caecum of the non-ruminant; marked feed studies have been u t i l i z e d to demonstrate the extent of digestion of any nutrient. The intestinal tract of the beaver i s anatomically similar to the intestinal tract of the horse, i n both the stomach i s simple and the caecum greatly enlarged. The present study i s centered on this organ. - 2 -An attempt has been made to establish the presence of cellulose digestion, to find the site of i t , and i f possible to isolate the bacteria responsible for the digestion. The experimental procedures which follow are given i n the order of completion rather than i n what might be considered the normal sequence. The bacteriological study was carried out f i r s t , the i n vit r o study of the site of digestion followed, with the determination of digestion at the end. It w i l l be obvious to the reader that i f any part i n sequence had been successful the subsequent experiments would have been unnecessary. The results of each division lead to the next experiment. - 3 -LITERATURE SURVEY A. Food Habits of the Beaver (Castor canadensis). Before going into a detailed study of the digestive processes of the beaver, i t i s advisable to gain some knowledge of the foods eaten by these animals i n the wild. In the following pages are tables l i s t i n g the trees and other plant materials eaten by beaver. This information has been obtained from a review of a part of the extensive literature available on this subject. Some plants occur in only one paper, others occur i n many of the papers reviewed. Food material eaten by the beaver varies with the time of the year. In the spring; grasses, water plants, low growing broad leafed plants, and shoots of shrubs are eaten. In fact, any plant growing i n or around the beaver pond i s consumed. Tuberous roots are eaten, especially those of the water l i l i e s and the rhizomes of bracken. Table I l i s t s the plants which are a part of the spring and early summer diet. Some of the plants are eaten i n toto; while only the leaves and stems of others are consumed. As the year progresses the beaver continues to eat the low growing plants. When the supply of shrubs and grass becomes insufficient the beaver ingests the bark, twigs, and leaves of small trees. Deciduous trees, especially poplar, willow, alder, and birch are f e l l e d at this time for food. At times conifers are fel l e d and some bark eaten. The roots of hemlock are often chewed. In the f a l l , tree f e l l i n g , for which the beaver i s so well known, i s underway; the branches and leaves of aspen, willow, birch and poplar - 4 -TABLE I Plant Material eaten by the Beaver (Castor canadensis) i n the United States and Canada. PLANT SCIENTIFIC NAME LOCALITY REFERENCE Arrowhead Aster Bedstraw Blackhaw Bracken Bramble Buck-bush Bulrushes Bur-reed Button-bush Cat-t a i l Chick Weed Shrubby Cinquefoil Coon Ta i l Sagittaria spp. Aster conspicuus Galium Black Berry Rubus spp. Viburnum lentago  Pteris aquilina Rubus spp. R. idaeus Symphoricarpos  occidentalis Scirpus spp. Typha l a t i f o l i a Stellaria borealis Potentilia Cht., Col. B.C. Yellowstone Pk. Col., N.Y. N.Dakota Cnt. Wise. Cnt. Man., N.Y. N.Dakota B.C., Col., Me. Col. N.Y. Wash., Col., Man., Wise. Man. Col. Ceratophyllum spp. Me. Daniel, 1957; Denney, 1952. Cottle, 1951. Warren, 1926. Denney, 1952; Tevis, 1950. Hammond, 1943-Daniel, 1957; Gibson, 1957; Hammerstrom '&•: Blake, 1939. Daniel, 1957; Gibson, 1957-Bailey, 1927; Green, 1936; Johnson, 1927; Tevis, 1950. Hammond, 1943. Cottle, 1951; Denney, 1952; Hodgdon & Hunt, 1955. Denney, 1952. Johnson, 1927. Beer, 1942; Denney, 1952; Green, 1936; Hammerstrom & Blake, 1939-Green, 1936. Retzer et a l . , 1956. Hodgdon & Hunt, 1955. - 5 -TABLE I - Cont'd. PLANT SCIENTIFIC NAME LOCALITY REFERENCE Corn Zea mays Cow Parsnip Heracleum High Bush Cranberry Spreading Dogbane Duck Potato Duck Weed Eelgrass Eelgrass Sweet Gale H. maximum Viburnum  trilobum Apocynum androsaemifolium Sagittaria spp. Lemna Potamogeton Vallisneria  americana Myrica gale Wild Geranium Geranium spp. Golden Rod Solidago Grass - - - -Grass Gramineae Horsetail Juneberry Leather Leaf Water L i l y Equisetum spp. Amelanchier spp. Chamaedaphne  calyculata Mich., Ala., Miss., W.Va. Yellowstone Pk. Mont. N. Dakota Cnt. Mich. Mich. Mich., B.C. N.Y. Cnt. Yellowstone Pk. Col. Cnt. Wash., B.C., Yellowstone Pk. Pond L i l y Numphaea (Yellow) B.C., Cnt. B.C., Cnt. Cnt. Col. Mich. Atwood, 193&; Denney, 1952. Warren, 1926. Townsend, 1953-Hammond, 1943-Gibson, 1957-Bradt, 1947-Bradt, 1947-Bradt, 1947; Cottle, 1951. Tevis, 1950. Daniel, 1957; Gibson, 1957-Warren, 1926. Denney, 1952. Gibson, 1957-Beer, 1942; Cottle, 1951; Hammerstrom & Blake, 1939; Warren, 1926. Cottle, 1951} Gibson, 1957-Cottle, 1951; Gibson, 1957-Daniel, 1957; Gibson, 1957-Denney, 1952; Retzer et a l . , 1956. Bradt, 1947-- 6 -TABLE I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Pond Lily-Rushes B r i s t l y Sarsapilla Sedge N. advena Water L i l y N. odorata Pond L i l y N. polysepala (Yellow) Water L i l y Nymphozanthus Water L i l y Nuphar spp. N. luteum Pond L i l y N. polysepala Mint . Mentha arvensis Mushroom Agaricaceae Pondweed Potamogeton P. ill i n o e n s i s Reed Phragmites Wild Rose Rosa spp. R. blanda  R. nitida  Juncus spp. Aralia hispida Carex spp. Ont. Cnt. Yellowstone Pk. Mich. Me. B.C. Man., Mont. B.C. Mich., Ont., Wise. Mont. Col. B.C., Wise, N. Dakota, Yellowstone Pk. Man. Man. Cnt. Wise. B.C., Col., Wise., Me. Daniel, 1957; Gibson, 1957-Daniel, 1957; Gibson, 1957. Warren, 1926. Bradt, 1947-Hodgdon & Hunt, 1955. Seton, 1929-Cottle, 1951. Green, 1936; Townsend, 1953. Cottle, 1951. Bradt, 1947; Daniel, 1957; Gibson, 1957. Hamerstrom & Blake, 1939; Townsend, 1953. Retzer et a l . , 1956. Cottle, 1951; Hamerstrom & Blake, 1939; Hammond, 1943; Warren, 1926. Green, 1936. Green, 1936. Gibson, 1957. Hamerstrom St Blake, 1939-Cottle, 1951; Denney, 1952; Hamerstrom & Blake, 1939; Hodgdon & Hunt, 1955; Retzer et a l . , 1956. - 7 -TABLE I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Sedge Beaked Sedge Sloughgrass Solomon's Seal Spatterdock Spiraea Water Starwort Strawberry-Thistle Vetch Viburnum Water Arum Water Raisin Water Shield Rynchospora Spartina michauxina Ont. Mont. Man. Polygonatum Yellowstone Pk. Nymphaea microphylla Man. Spiraea spp. Callitriche  palustris Fragaria  virginiana Vicia americana Ont. Mont. Man. Yellowstone Pk. B.C. Viburnum spp. Me. Calla palustris Cnt. Viburnum cassinoides Ont. Cnt. Brasenia schreberi Col. Water wally - -Water-weed Anacharis canadensis N.Y. Water-weed KLodea canadensis Mich. Winter Berry Hey v e r i c i l l a t a Cnt. Gibson, 1957; Seton, 1929-Townsend, 1953-Green, 1936. Warren, 1926. Green, 1936. Daniel, 1957. Townsend, 1953-Green, 1936. Warren, 1926. Cottle, 1951. Hodgdon & Hunt, 1955. Gibson, 1957-Gibson, 1957-Daniel, 1957; Gibson, 1957. Denney, 1952. Tevis, 1950. Bradt, 1947-Gibson, 1957-- 8 -are stored i n the bottom of the beaver pond for winter food. Many-different trees (Table II) are felled and some of the bark and twigs are removed, and from the following l i s t of trees i t w i l l be noted that there are few trees not cut by the beaver. A number of observations given are of single trees eaten i n areas with a definite shortage of the preferred aspen, willow, birch and poplar group. In reviewing the literature pertaining to the eating habits of the beaver, reference i s often made to Castor fiber, the European River Beaver. It i s of interest to note similarities and differences between these two species with respect to food material eaten. From Table I I I i t w i l l be seen that the same genera of plants are consumed, as one would expect, the species name, where given, i s different. In Norway; poplar, birch, aspen, oak, alder, apple and mountain ash are the winter feed materials, (Leighton, 1935, Salvesen, 1928). Aquatic plants are the summer food. An interesting fact noted by Leighton (1935) i s that the river beaver does not eat the l i l y pads. Just the stem, f r u i t , and root of the pond and water l i l i e s are consumed. From the Russian literature a very comprehensive l i s t of the trees u t i l i z e d as winter feed i s obtainable (Table I I I ) . Willow, rather than poplar, i s mentioned as the preferred food of the river beaver. In Russia, as i n Norway, Castor fiber does not eat l i l y pads. The spring and summer diet i s made up of the same type of plant materials as that eaten by the beaver i n America (Table (*P7). TABLE I I . Trees Cut by the Beaver (Castor canadensis) in the United States and Canada. PLANT SCIENTIFIC NAME LOCALITY REFERENCE Alder Alnus Col., N.Y., Yellowstone Pk. Apple Ash Basswood Bay Beech A. glutinosa A. incana A. rugosa A. sitchensis A. tenuifolia Pyrus malis Fraxinus F. americana  F. nigra F. pennsylvanica T i l i a americana Perm. Wise, Me., N.Y. Miss., Mass., Me. B.C. Mont. Perm., N.Y. Col., Ont., N.Y. Fagus grandifolia Ont., N.Y. Ont., Me., N.Y. N.Dakota N.Y. Ala. N.Y. Aldous, 1938; Bailey, 1927; Denney, 1952; Johnson, 1927; Retzer et a l . 1956; Shadle & Austin, 1939; Warren, 1926. Anonymous, 1942. Hamerstrom & Blake, 1939; Hodgdon & Hunt, 1955; O'Brien, 1938; Tevis, 1950. Atwood, 1938; Denney, 1952; Hazeltine, 1950. Cottle, 1951. Townsend, 1953-Anonymous, 1942; Shadle et a l . 1943; Tevis, 1950. Bailey, 1927; Denney, 1952; Gibson, 1957; Shadle et a l . , 1943-Daniel, 1957; Tevis, 1950. Daniel, 1957; Hazeltine, 1950; Johnson, 1927. Hammond, 1943-Shadle et a l . . 1943; Tevis, 1950. Denney, 1952. Johnson, 1927; Shadle et a l . , 1943. - a o -TABLE I I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Birch Betula spp. Penn. Col., , B.C., N.Y. Anonymous, 1942; Bailey, 1927; Cottle, 1951; Denney, 1952; Seton, 1929; Shadle et a l . , 1943. Bog Birch Betula Col. Retzer et a l . , 1956. Birch B. fontinalis Yellowstone Pk. Warren, 1926. Black Birch B. lenta N.Y. Tevis, 1950. Yellow Birch B. lutea Cnt., N.Y. Daniel, 1957; Gibson, 1957; Johnson, 1927. River Birch B. nigra Miss. Atwood, 1938. Paper Birch B. papyrifera Ont., N.Y., Aldous, 1938; Me. Daniel, 1957; Gibson, 1957; Hamerstrom & Blake, 1939; Hodgdon & Hunt, 1955; Johnson, 1927; O'Brien, 1933. Grey Birch B. populifolia Me. Hodgdon & Hunt O'Brien, 193S. , 1955; Blue Birch Carpinus caroliniana Col., N.Y. Denney, 1952; Shadle, 1954; Shadle & Austin, 1939; Shadle et a l . , 1943. White Cedar Thu.ia occidentalis Ont., Me. N.Y., Gibson, 1957; Hodgdon & Hunt Johnson, 1927; O'Brien, 1938. , 1955; Red Cedar Thu.ia plicata B.C. Cottle, 1951. Cherry Prunus Ont., N.Y. Me., Gibson, 1957; Hodgdon & Hunt Shadle et a l . , , 1955; 1943. Pin Cherry P. pemsylvanica Penn. Wise. , Cnt., , N.Y. Anonymous, 1942; Bailey, 1927; Daniel, 1957; Hamerstrom & Blake, 1939; Johnson, 1927; Shadle & Austin, 1939; Tevis, 1950. - 1 1 -TABLE I I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Black Cherry- P. serotina N.Y. Tevis, 1950. Choke Cherry- P. virginiana Ont., N.Dakota, Daniel, 1957; N.Y., Yellowstone Hammond, 1943; Pk. Tevis, 1950; Warren, 1926. Dogwood Cornus Cal. Bailey, 1927; Denney, 1952. C. obliqua Miss. Atwood, 1938. C. racemosa Miss. Atwood, 1938. Red Osier Dogwood C. stolonifera N.Dakota, N.Y., Mont. Aldous, 1938; Hammond, 1943; Johnson, 1927; Townsend, 1953. Elm Ulmus N.Y. Shadle, 1954; Shadle et a l . . 1943-U. americana Mich., Miss., N. Dakota. Atwood, 1938; Hammond, 1943. U. thomasi Mich., Miss. Atwood, 1938. F i r Abies Cal. Denney, 1952. Balsam Fir A. balsamea Ont., Me., N.Y. Daniel, 1957; Gibson, 1957; Hodgdon & Hunt, 1955; Johnson, 1927; O'Brien, 1938. Douglas Fir Pseudotsuga menziesii B.C., Yellow-stone Pk. Cottle, 1951; Warren, 1926. Black Gum Nyssa sylvatica Ala. Denney, 1952. Tupelo Gum Nyssa bi f l o r a Ala. Denney, 1952. Red Gum Sweet Gum Eucalyptus rostrata Liquidamber styraciflua Ala. Ala. Denney, 1952. Denney, 1952. Hawthorn Crataegus douglassi Wash., N.Y. Beer, 1942; Tevis, 1950. Hazelnut Corylus spp. Ont. Daniel, 1957; C. americana Aldous, 1938. 12 -TABLE I I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Beaked Hazel C. cornuta California Hazel Hemlock Tsuga T. canadensis Ironwood Juniper Red Cedar Maple J. virginiana Acer Manitoba Maple Red Maple A. rubrum Silver Maple A. saccharinum Sugar Maple A. saccharum Mountain Maple A. spicatum Cnt., Me. Cal. Perm., Me., N.Y. Cnt. Ostrya virginiana Cnt., N.Y. Juniperus communis Cal., Mont. Mich., Miss. Mich., Ala., N.Y. A. negundo Miss., N.Dak. Striped Maple A. pemisylvanicum Ont. Ont., Me., N.Y. Mich., Miss., N.Y. Ont., N.Y. Ont. Gibson, 1957; Hodgdon & Hunt, 1955-Bailey, 1927; Denney, 1952. Anonymous, 1942; Bailey, 1927; Hodgdon & Hunt, 1955; Johnson, 1927; Shadle et a l . , 1943. Daniel, 1957; Gibson, 1957. Daniel, 1957; Shadle et a l . , 1943 • Denney, 1952; Townsend, 1953-Atwood, 1938. Bradt, 1947; Denney, 1952; Shadle et a l . , 1943-Atwood, 1938; Hammond, 1943. Bailey, 1927; Daniel, 1957. Daniel, 1957; Gibson, 1957; Hazeltine, 1950; Hodgdon & Hunt, 1955; Johnson, 1927; O'Brien, 1938; Shadle & Austin, 1939-Atwood, 1939; Shadle, 1954. Daniel, 1957; Gibson, 1957; Shadle, 1954; Tevis, 1950. Bailey, 1927; Daniel, 1957; Gibson, 1957. Wm I I - Contfd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Mountain Ash Sorbus americana Mountain Holly Oak Quercus White Oak Red Oak Q. alba Q. borealis Scarlet Oak Q. coccinea Bur Oak Q. macrocarpa Chinquapin Oak Q. muhlenbergii Red Oak Q. rubra Pine Jack Pine Pinus P. banksiana Lodgepole Pine P. contorta Yellow Pine P. ponderosa Norway Pine P. resinosa Pitch Pine P. rigida White Pine P. strobus N.T.. N.Y. Cal. Mich., Miss., N.H. Mich., Miss., Ont. Mich., Miss. N. Dakota. Mich., Miss. Me., N.Y., N.H. Penn., Cal. Johnson, 1927-Johnson, 1927-Bailey, 1927; Denney, 1952; Hamerstrom & Blake, 1939. Anonymous, 1942; Atwood, 1938; Jahoda, 1946. Atwood, 1938; Daniel, 1957-Atwood, 1938. Hammond, 1943. Atwood, 1938. Hodgdon & Hunt, 1955; Jahoda, 1946; Tevis, 1950. Anonymous, 1942; Denney, 1952. Yellowstone Pk. Bailey, 1927. Yellowstone Pk., B.C., Col., N.Y., Mont. Bailey, 1927; Cottle, 1951; Retzer et a l . , 1956; Shadle et a l . , 1943; Townsend, 1953; Warren, 1926. Yellowstone Pk. Bailey, 1927. Yellowstone Pk., Ont. Me. Ont., Me., N.Y. Bailey, 1927; Daniel, 1957; Gibson, 1957-Hodgdon & Hunt, 1955. Daniel, 1957; Gibson, 1957; Hodgdon & Hunt, 1955; Johnson, 1927. - 14 -TABLE I I - Cont'd PLANT SCIENTIFIC NAME LOCALITY REFERENCE Poplar Populus Cottonwood P. deltoides Penn., Mich., Me., N.Y. Col., N. Dak., N.Y., Yellowstone Pk. Aspen P. grandidentata Me., Ont., N.Y. Aspen P. tremuloides Shadblow Amelanchier  canadensis Spruce Picea Engelman P. engelmanni Spruce Penn., Wash., Col., N.Y., Wise, Me., Yellowstone Pk., B.C., Man., Ont., Minn. N.Y. B.C., N.Y. Col., Mont., Yellowstone Pk. Anonymous, 1942; Bailey, 1927; Bradt, 1947; Hodgdon & Hunt, 1955; Shadle et a l . , 1943. Bailey, 1927; Denney, 1957; Hammond, 1943; Johnson, 1927; Warren, 1926. Bailey, 1927; Daniel, 1957; Gese & Shadle, 1942; Hazeltine, 1950; Johnson, 1927; O'Brien, 1938; Shadle, 1954; Stegeman, 1954. Aldous, 1938; Anonymous, 1942; Bailey, 1927; Beer, 1942; Cottle, 1951; Daniel, 1957; Denney, 1952; Gese & Shadle, 1943; Gibson, 1957; Green, 1936; Hamerstrom & Blake, 1939; Hazeltine, 1950; Hener, 1938; Johnson, 1927; O'Brien, 1938; Retzer et a l . , 1956; Seton, 1929; Shadle, 1954; Shadle & Austin, 1939; Stegeman, 1954; Tevis, 1950; Townsend, 1953; Warren, 1926. Bailey, 1927; Shadle, 1954; Tevis, 1950. Bailey, 1927; Cottle, 1951; Johnson, 1927; Shadle et a l . , 1943-Retzer et a l . , 1956 Townsend, 1953; Warren, 1926. - 15 -TART.F. TT - ContM PLANT SCIENTIFIC NAME LOCALITY REFERENCE White Spruce P. glauca Black Spruce P. mariana Red Spruce Sycamore Tamarach Willow Willow Cnt. Ont., Me. P. rubens Me. Platanus occidentalis Mich., Miss. Larix laricina Me., Ont. Salix S. interior Penn., Mich., N.Y., Wash., Col., N. Dak., Cnt., Wise, Me., Yellow-stone Pk., B.C. Miss. Witch-hazel S. longifolia  S. longipes  S. lucida  S. nigra  S. pedicellaris  Hamamelis virginiana N.Y. Man. Miss. Man. Miss. Man. • Daniel, 1957j Gibson, 1957-Daniel, 1957; Gibson, 1957; Hodgdon & Hunt, 1955-Hodgdon & Hunt, 1955-Atwood, 1938. Bailey, 1927; Gibson, 1957; Hodgdon St Hunt, 1955-Aldous, 1938; Anonymous, 1942; Bailey, 1927; Beer, 1942; Bradt, 1947; Cottle, 1951; Daniel, 1957; Denney, 1952; Gibson, 1957; Hamerstrom St Blake, 1939; Hodgdon & Hunt, 1955; Johnson, 1927; O'Brien, 1938; Retzer et a l . , 1956; Shadle & Austin, 1939; Shadle et a l . , 1943; Tevis, 1950; Townsend, 1953; Warren, 1926. Atwood, 1938; Hammond, 1943-Green, 1936. Atwood, 1938. Green, 1936. Atwood, 1938. Green, 1936. Shadle et a l . , 1943-- 16 -TABLE I I I Trees Cut by the Beaver (Castor fiber) in Russia PLANT SCIENTIFIC NAME Alder ALnus incana, Moenh (Semyonoff, 1951) Birch Betula verrucosa, Ehrh (Semyonbff:,/1951) Zhdanoff, 1951) B. pubescens L. Bird-cherry Prunus padus L. (Semyonoff, 1951; Zhdanoff, 1951) F i r (Semyonoff, 1951) Mountain ash Sorbus aucuparia L. (Semyonoff, 1951; Zhdanoff, 1951) Pine (Semyonoff, 1951; Zhdanoff, 1951) Poplar Populus (Popoff, 1955; Fomicheva, 1955; Semyonoff, 1951; Zhdanoff, 1951) P. tremula L. Siberian Stone Pine (Zhdanoff, 1951) Willow Salix spp. (Popoff, 1955; Fomicheva, 1955; Semyonoff, 1951; Zhdanoff, 1951) TABLE IV Some Plants Eaten by the Beaver (Castor fiber)in Russia (Semyonoff, 1951) PLANT PLANT PLANT Agropyron Diecian Nettle Marsh-marigold Angelica sylvestris Forest Horse-tail Ragwort Arrowhead Forest Raspberry Ranunculus spp. Avens Golden-rod Reeds Buckbean Great Willow-herb Sedge Lake and Forest Marsh Cinquefoil Sow-thistle Bulrushes Canary-grass Marsh Horse-tail Spiraea Cat-tail Marsh and Creeping Trefoil Sweet Grass Coltsfoot Meadowsweet Water-lily Cranberry Nettles Wild Rose Black Currant Gout-wort Yarrow Red Currant Pond-lily -17 -The amount of feed eaten by the beaver i s of concern to the conservationist. The number of animals i n a given area i s directly related to the individual food requirements and the amount of food available. There are two methods of calculating food intake; by actual observations, and through calculations based on caloric requirements. The method i n common usage in the wild l i f e f i e l d i s based on observations, the number of trees felled by a given number of animals per year. Only part of each tree i s eaten by the beaver: the leaves, the twigs down to a quarter of an inch, and the bark stripped down to areas four inches in diameter. Calculations on the percentage u t i l i z a t i o n of any given tree have been given by Aldous (1938) from observations on 456 aspen. The degree of u t i l i z a t i o n of any tree i s at most 36 per cent of the wet weight of the tree. Calculating from the same observations Aldous (1938) suggested a consumption of between 1.4 and 2.1 pounds of food material each day. Stegeman (1954) actually weighed the food material and calculated, from known numbers of trees f e l l e d and animals present i n an area i n New York, a food intake of five pounds of aspen by wet weight, per beaver per day. The beaver eats bark and twigs nine months of the year, the consumption for this period being 1500 pounds of aspen per beaver (Stegeman, 1954). Green feed was supplied to a group of beaver in Colorado. From the amount of aspen supplied on contract, Warren (1940) calculated that a beaver eats one ton of aspen per year. O'Brien (1938) gives the daily food intake for two beaver as between 1.4 and 12.9 pounds (Table V); these figures are for wet weight. The branches of the designated trees were placed free i n the enclosure. Food intake was calculated as the decrease in weight of these branches over a 24-hour period. No allowance was made for the amount of weight which might have been lost through - 18 -drying of the branches over the time period. The beaver also built a nest from the sticks and in the winter months stored food i n the nest box. The "weights given i n March and Apri l are especially influenced by the nest building. A more c r i t i c a l method i s necessary for exact measurement of food intake. TABLE V Food Intake of Two Beaver (Castor canadensis) i n Captivity (O'Brien, 1938) MONTH NUMBER OF DAYS DAILY AVERAGE WT. FOOD IN LB. AVERAGE DIAMETER OF TREES IN IN. TREE TYPE Sept. 26-30 4 6.6 2.8 Aspen Oct.1-7 7 8.3 2.0 Aspen Oct.8-14 7 8.5 2.2 Aspen Oct.15-21 7 9-6 2.5 Aspen Oct.22-31 10 7.6 2.0 Aspen Nov.1-10 10 9.9 2.0 Aspen Nov.11-17 7 1.5 7-3 Maple Nov.18-26 9 1.4 2.0 Birch Dec.1-7 7 6.0 2.8 Aspen Dec.8-lA 7 6.5 2.8 Aspen Dec. 15-21 7 7.4 2.7 Aspen Dec. 22-31 10 8.1 3.0 Aspen Jan. 1-7 7 7.8 3.0 Aspen Jan. 8-14 7 7.0 3.0 Aspen Jan. 15-21 7 6.8 2.5 Aspen Jan. 22-31 10 6.2 2.7 Aspen Feb. 1-14 14 2.1 2.0 Alder Feb. 19-28 10 9.4 Willow Mar. 1-14 14 10.5 Willow Mar. 15-31 : 17 12.9 Willow Apr. 1-14 14 11.2 Willow . Another method of calculating the food intake of the beaver i s by observations on the number of trees felled per year rather than on the exact poundage food intake. Bradt (1947) calculated that a beaver f e l l s either for food or dam building 365 trees per year; one tree varying i n diameter from one to three inches per beaver per day. These calculations are based on six captive beaver working on a stand of poplar. - 19 -A l l these figures are of use only as a very general guide to the rate of destruction of a stand of trees by a colony of beaver. They are of use i n the f i e l d but give no exact value of food intake. The , true picture of food requirements has been calculated by Stephenson (1956). The average body weight of an adult beaver was calculated and the actual caloric requirement was estimated from Brody (1945). Tables giving the chemical composition of plant materials were consulted and the caloric value computed. From these calculations the beaver could be expected to eat 1.8 to 2.0 pounds per day for maintenance. Gibson (1957), using the same formula as Stephenson (1956), calculated a food intake of 14,000 pounds of aspen bark per year. This figure must be the intake for the colony of three adults and six kit s under study, rather than for any individual animal. From the context i t i s d i f f i c u l t to know what i s intended. For a beaver, the intake values of wet weights of bark, leaves, and twigs may be listed as follows: Aldous (1938) 1.4 to 2.1 pounds daily Stegeman (1954) 5 pounds daily Warren (1940) 5.5 pounds daily O'Brien (1938) .7 to 6.3 pounds daily Stephenson (1956) 1.8 to 2.0 pounds daily maintenance. Gibson (1957) Approximately 6 pounds daily From these figures i t w i l l be noted that there i s the same variation i n the observed values as in the computed values. It may be concluded that a beaver eats from .7 to 6 pounds of food material daily by wet weight. - 20 -B. Composition and Digestibility of Plant Carbohydrates: To carry out satisfactorily studies related to food material, a standard method for determining the chemical composition of plant material i s essential. For analytical purposes, plant material i s considered to be composed of certain chemically distinct fractions. These fractions are: moisture, protein, ether extract, crude fiber, nitrogen-free extract (N.F.E.), and ash. The carbohydrate fraction i s computed as the difference between 100 and the sum of the percentages of moisture, protein, ether extract and ash. The carbohydrate material i s divided into crude fiber, starch, dextrin, sugars, and other indeterminate solids; or into crude fiber and N.F.E. Digestibility of dietary carbohydrate does not follow the generally accepted partioning into crude fiber and N.F.E. By common definition, crude fiber i s the fibrous poorly digested part of the plant material. It i s composed of lig n i n , cellulose, hemicellulose and pentosans. Lignin, which i s 97.8 to 99-3 per cent recovered i n the feces of rabbits and steers (Crampton et a l . , 1938) i s chemically part of the N.F.E. Cellulose, which i s digested, i s included i n the crude fiber fraction. Carbohydrates i n nutritional studies should be divided biologically rather than chemically. Plant c e l l walls are made up of lignin, cellulose, and hemicellulose. Lignin, which occurs generally as lignocellulose i s indigestible. The chemical structure of lignin i s not known definitely, but i t has a greater percentage of carbon than true carbohydrates. Cellulose i s not a single chemical substance but i s a carbohydrate made.up of 'n* molecules of glucose. Cellulose i s very resistant to chemical breakdown. The hemi-celluloses comprise a group of carbohydrates of high molecular weight that resemble cellulose but are more soluble and more easily decomposed. -21 -Crampton and Maynard (1938) suggested dividing the carbohydrates into three categories; the practically non-digested fraction, other carbohydrates, and cellulose which i s chemically recognizable. Weede (in Sijpesteijn, 1948), calculated crude fiber as representing cellulose with modifications because the chemicals used i n the determination of fiber remove some of the cellulose. Hay, according to Ritman et a l . (in Sijpesteijn, 1948) i s composed of 10.7 per cent l i g n i n , 20.8 per cent xylan, 33.1 per cent hexosan or cellulose, and 34-9 per cent crude fiber. Plant material eaten by the beaver in the spring and summer consists of the rapidly growing soft plants (Table I ) . The percentage of crude fiber tends to rise slightly in the plant tissues as the plant matures (Table VI). Slow growth which occurs as the plants mature i s favourable to l i g n i f i c a t i o n . The percentage of protein tends to drop from early leaf through f u l l bloom to dry leafage. Plants i n the lush growing season, contain a higher percentage of cellulose i n relation to lignin than later i n the season. TABLE VI. Percentages of Protein and Fiber in the Dry Matter of Quercus douglasi as the Tree Matures. (Gordon et a l . , 1939) STAGE OF PLANT PROTEIN FIBER Young leaves 30.56 11.50 Leaves developed 14.76 14.02 Leaves mature 12.26 13.40 Leaves more mature 9.50 12.97 Tree leaves are more digestible than twigs; some trees have leaves which compare favourably with good hay i n food value. Leaves of ash, birch, linden, and alder are valuable for feed in that order - 22 -TABLE VII Composition of Some Plants Eaten by the Beaver (Castor canadensis) PLANT MOISTURE PER CENT PROTEIN PER CENT FIBER PER CENT N.F.E. PER CENT Corn (Morrison, 1948) 71.6-80.6 1.5-2.6 5.8-8.3 10.2-14-3 Sedge (King et a l . 1944) 9.86 2.6 8.96 55.41 Aspen (Cowan et al.,1950) 46.34 7.1 28.07 52.95 Bog Birch (Cowan et a l . 1950) 34.99 6.1 27.17 56.40 Paper Birch (Cowan et a l . 1950) 43.75 6.98 29-78 52.01 Dogwood (Cowan et a l . 1950) 46.66 4.84 28.75 57.53 Douglas F i r (Cowan et al.(1950) 50.27 6.53 19-91 62.74 Hazel Browse (Cowan et al.1950) 1 yr. growth 2 yr. growth 3 yr. growth 45.36 43-98 38.41 40.07 6.58 7-96 5.12 4.11 26.75 23.25 31.75 41.62 59.13 50.02 56.12 50.01 Lodgepole Pine (Cowan et al.1950) 54.3 6.9 24-98 57-23 Engleman Spruce (Cowan et al.1950) 47.51 5.4 21.58 60.75 Swamp Willow (Cowan et al.1950) 49.77 6.32 23.99 61.92 Willow Browse (Fagan et al.1932) 43.10 5.91-7.5 31.86-35-0 55.18-50.1 1 yr. growth (Cowan et al.1950) 43.10 7.22 31.73 54.1 2 yr. growth (Cowan et al.1950) 43.10 5.69 38.72 50.2 - 23 -(Morrison, 1948). Chemical analysis of aspen, hazelwood, dogwood, red maple, and oak show the leaves of these plants to be better fodder than blue grass (Hellmers, 1940) on a per cent composition basis; d i g e s t i b i l i t y i s not included i n this calculation. Table VII gives the chemical composition of some plants eaten by the beaver. The rate of digestion of cellulose varies from animal species to animal species. In the sheep, Gray (1947), calculated a digestion of 4 0 to 45 per cent of the ingested cellulose before the food reaches the abomasum, 15 to 20 per cent i n the small intestine, 7 to 11 per cent i n the caecum and 4 to 9 per cent i n the colon. A total of 6 0 per cent of the cellulose ingested i s broken down in the sheep's digestive tract. Kellner and Fingerling (in Sijpesteijn, 1948) estimated that ruminants digest 7 0 to 75 per cent of the cellulose ingested. Ellenberger (in Sijpesteijn, 1948) calculated 15 to 30 per cent digestion of cellulose i n the caecum of the cow. In the caecum of the horse Kellner and Fingerling (in Sijpesteijn, 1948) estimated a 21 to 57 per cent digestion of cellulose. Conrad et a l . (1958) calculated a digestion of 48.2 per cent in 72 hours to 55.1 per cent in 100 hours of marked cellulose in the rat. This digestion would take place i n the caecum. Forbes et a l . (1952) l i s t e d the digestion of cellulose i n the pig as varying from 41 to 68 per cent. This variation was due to the degree of li g n i f i c a t i o n of the cellulose, as well as to the amount of cellulose i n the normal diet of the pigs. Woodman and Evans (1947) feeding the identical diets to pigs and sheep calculated a digestion of true cellulose plus xylen, the sum of crude fiber plus N.F.E., as 82.1 per cent in pigs and 81.8 per cent in sheep. C. Mode of Digestion of Plant Cellulose: No cellulase has as yet been isolated from the digestive juices of mammals. Kitts et a l . (1957) could demonstrate no cellulase i n the - 24 -digestive tract of the beaver. It seems safe to conclude that the digestion of cellulose, wherever i t occurs i n the mammalian digestive tract, i s brought about by micro-organisms. Baker and Martin (1938) demonstrated lacunae eroded .. out of pieces of plant material from the rumen of cattle and the caecum of horses, rabbits and guinea pigs. The bacteria responsible for this erosion can be seen with proper staining methods. It i s d i f f i c u l t , however, on the plating of intestinal bacteria, to distinguish between the transient passengers and the permanent residents of the gastro-intestinal tract. Most bacteria, which are demonstrable on direct smear and staining, have not been cultured on the media customarily used i n th i s type of study. Gall and Huhtanen (1951) set up five c r i t e r i a for true cellulose-digesting bacteria from the digestive tract. These c r i t e r i a can be d i f f i c u l t to meet as animals on different diets have different intestinal f l o r a (Baker, 1942; Baker, 1945; Bryant et a l . . 1953b; Burroughs et a l . , 1950; ELsden, 1945; Hamilton, 1942). There i s specificity of intestinal bacteria; guinea pigs and rabbits i n the same pen on a similar diet have different bacterial flora. (Baker, 1945). Many workers (Bryant et a l . , 1953a; Doetsch et a l . 1952; H a l l , 1952; Hungate, 1950; Kitts et a l . , 1954; Marston, 1948), have successfully cultured cellulose-digesting organisms from the digestive tract of ruminants and non-ruminants; there are also some workers who have had no success in culturing the same or different bacteria. Of the extensive and conflicting literature, Sijpesteijn (1948) gives a particularly comprehensive resume, dealing especially with those bacteria which digest cellulose in the rumen of the cow. - 25 -The cellulose-digesting bacteria produce volatile fatty acids as by-products of digestion. Marshall et a l . (1945) give the end products of digestion as being the lower fatty acids plus methane. Barcroft (1945)> calculated the amount of volatile fatty acid i n the veinous system of various animals (Table VIII). TABLE VIII. Average Amount of Volatile Fatty Acid i n Blood from Various Blood Vessels of Different Animals. Expressed i n ml. N/100 A l k a l i Needed to Neutral-ize the Volatile Fatty Acid i n 100 ml. Blood. (Barcroft, 1945). ANIMAL VEIN DRAINING RUMEN VEIN DRAINING SMALL INTESTINE VEIN DRAINING CAECUM Sheep 38 4 22 Rabbit — 4 23 Pig — 11 28 Pony 7 (stomach) 5 49 Stephenson (1956) gives the amount of volatile fatty acid in beaver blood i n milli-equivalents (m.e.). Comparison i s made by Stephenson between the quoted figures of McLendon of 0.0003 m.e. of vo l a t i l e fatty acid i n the blood of humans and dogs and the calculated figure of 0.0021 m.e. for cattle, and 0.0019 m.e. for beaver. Table IX gives the readings obtained by Stephenson (1956) for beaver blood. TABLE IX. Volatile Fatty Acids i n Beaver Blood — Milli-Equivalents Time 10 - 2 per 100 ml. of Blood. (Stephenson, 1936). YEARLINGS ADULTS ALLPBEAVER Mean and Standard Error 19.04 - 1.51 18.53 * 2.03 18.78 - 1.23 Standard Deviation 4.52 6.42 5-38 Range 10.6 - 25.5 9.9 - 32.3 9-9 - 32.3 The breakdown of carbohydrate influences the blood sugar level. There i s some question as to the exact by-products of bacterial digestion of cellulose which are absorbed by the blood, but they can be taken as influencing the amount of blood sugar. The blood sugar levels of several animals are given i n Table X for comparison between various animal species. TABLE X Per cent of Blood Sugar i n the Circulation of Various Animals ANIMAL RANGE Cow (Dukes, 1955) 40-60 Sheep (Dukes, 1955) 40-65 Horse (Dukes, 1955) 60-110 Pig (Dukes, 1955) 40-250 Dog (Dukes, 1955) 70-100 Deer (Bandy et a l . , 1957) 30-90 Beaver (Stephenson, 1956) 49-160 The blood of non-ruminants has a higher blood sugar level than the ruminants, and a lower volatile fatty acid content. The non-ruminant herbivores are between the carnivores and the ruminants i n both blood sugar level and volatile fatty acid level in the blood. This fact could be an indication of the importance of the digestion of cellulose by bacteria i n any animal species. Bacterial digestion of cellulose i s more extensive in ruminants than i n non-ruminant herbivores. MATERIALS A. Experimental Animals 1. Eleven beaver, Castor canadensis leucodontus, were obtained at various intervals between Ap r i l 1957 and June 1958 on Vancouver Island. These animals were shipped by a i r to the University of British Columbia. The beaver were designated by number in order of arriv a l and subsequent sacrifice. Five beaver were, sent from the Department of Lands and Forests, Ontario. These animals were dead - trapped for pelts; the intestinal tracts were removed, frozen, and sent by a i r to the University of Bri t i s h Columbia. 2. The rabbits used i n the comparative study were obtained from the University of British Columbia, Central Animal Depot. 3• The mink used i n the direct feeding study were obtained from the Division of Animal Science, University of British Columbia. B. Feed 1. The beaver were fed the U.B.C. 16-57 Ration. The composition of the ration i s given i n Table XI. This ration was fed ad libitum to a l l the animals. Small branches and leaves of some common deciduous trees, especially alder, were also provided and were eaten by some individuals. Water was not provided except for that i n the trough of the tanks. 2. In the direct feeding study the beaver, rabbit and mink were fed U.B.C. 16-57 Ration, finely ground, and mixed with chromic oxide at the one per cent level as a marker. This feed was mixed with water to a porridge l i k e consistency. - 28 -TABLE XI Composition of U.B.C. 16-57 Ration CONSTITUENT POUNDS Ground oats 400 Ground wheat 400 Ground barley- 300 Wheat bran 250 Molasses 100 Dried Grass 100 Soya meal (45-50 per cent) 100 O i l cake meal 100 Copra meal 100 Fish meal (70 per cent) 60 Bone meal 20 Iodized salt 20 Irradiated yeast 2 1952 TABLE XII Per Cent Proximate Composition of Ration 16-57 CONSTITUENT PER CENT AMOUNT Moisture 10.9 Crude Protein 18.1 Crude fiber 6.3 Cellulose 5.8 Ether extract 9-5 N.F.E. 49-4 Ash 5.8 C. Macroscopic Study: The entire digestive tract of a l l the sacrificed animals was ligated and removed for examination of the contents with respect to consistency and appearance. The beaver from Ontario were similarly handled after thawing. D. Microbiological Study The bacteria which digest cellulose in the gastro-intestinal tract of mammals are known to be d i f f i c u l t to culture. The media and materials used in this study were primarily those which had been used successfully by other workers (Tables XIII to XVII). Thioglycollate Medium (Table XVIII) was used as an experiment following disappointing results on other media. Some of the other media used, such as MacConkey, S.S., were used because of their a v a i l a b i l i t y and because of an interest i n the results which might be obtained. The caecal contents of the sacrificed animals were used as the inoculum. This material was removed using aseptic technique and collected i n sterile glass beakers or large mouthed screw-capped bottles. The inoculum was used directly or diluted using Solution 1 (Table XIII). A number of anaerobic media were used. The methods of Hungate (1950), Doetsch et a l . (1952), and Hall (1952) were followed for the isolation of the c e l l u l o l y t i c micro-organisms i n the caecal contents of the beaver and rabbit. The composition of these media are given i n Tables XIV and XX. TABLE XIII Solution 1. Dilution Blank Medium. (Doetsch et a l . , 1952; Hungate, 1950). CONSTITUENT AMOUNT Ammonium sulfate .05 gms. Potassium phosphate monoba sic .02 gms. Potassium phosphate dibasic .05 gms. Calcium chloride .005 gms. Magnesium sulfate .005 gms. Sodium chloride .1 gms. Sodium bicarbonate .4 gms. Sodium thioglycolate .05 gms. L-Cystine .075 gms. Glucose .05 gms. Rezasurin .001 gms. Dis t i l l e d water 100 ml. Preparation; (1) Prepare blanks the same day as they were used. (2) Combine ingredients in 1000 ml. flask. (3) Dispense into 100 ml. square milk dilution blank bottles. Ninety-nine - 30 -ml. were dispensed into a l l blanks except number one which contained 90 ml. (4) Autoclave for 15 minutes at 120°C. (5) Place rubber stoppers pierced with glass rods on the l i p of the bottles during autoclaving. (6) Replace stoppers as soon as possible after autoclaving to ensure anaerobiosis. Medium i s pale orange when anaerobic and pale pink i n the presence of small amounts of oxygen. (7) Include pieces of parchment paper i n dilution blanks prior to ster i l i z a t i o n . Strips two inches by half an inch were used. (8) Bubble carbon dioxide through medium for approximately two minutes prior to inoculation. TABLE XIV Anaerobic Agar Medium 1 (Doetsch et a l . , 1952; Hungate, 1950) CONSTITUENT AMOUNT Inorganic salt solution 2 Filtered rumen f l u i d Rezasurin Cellulose Agar 20.0:ml. 15.0 ml. 0.0001 gms. 1.0 gms. 2.5 gms. Preparation; (1) S t e r i l i z e at 120°C. for 15 minutes. (2) Cool, add 50 ml. of solution 3 which has been Seitz f i l t e r e d . (3) Make up to a total of 100 ml. with st e r i l e d i s t i l l e d water. - 31 -TABLE XV Anaerobic Agar Medium 2 (Doetsch et al.» 1952j Hungate, 1950) CONSTITUENT AMOUNT Eugon agar (B.B.L.) 4.45 gms. Agar 0.10 gms. Inorganic salt solution 2 20.0 ml. Solution 3 50.0 ml. Di s t i l l e d water to 100 ml. Prepare as Anaerobic Agar Medium 1. TABLE XVI Solution 2 CONSTITUENT AMOUNT Ammonium sulfate . Potassium phosphate monobasic Potassium phosphate dibasic Calcium chloride Magnesium sulfate Sodium chloride D i s t i l l e d water 0.05 gms. 0.05 gms. 0.02 gms. 0.005 gms. 0.005 gms. 0.1 gms. to 100 ml. TABLE XVII Solution 3 CONSTITUENT AMOUNT Sodium thioglycolate L.-Cystine Glucose Cysteine hydrochloride Sodium carbonate Sodium bicarbonate D i s t i l l e d water 0.1 gms. 0.155 gms. 0.4 gms. 0.04 gms. 0.6 gms. 0.5 gms. to 100 ml. - 32 -TABLE XVIII Anaerobic Agar Medium 3(Hall, 1952) CONSTITUENT AMOUNT-Sodium chloride 0.025 gms. Ammonium sulfate 0.01 gms. Potassium phosphate monobasic 0.02 gms. Potassium phosphate dibasic 0.01 gms. Calcium chloride 0.003 gms. Magnesium sulfate 0.003 gms. Sodium bicarbonate 0.5 gms. Cysteine hydrochloride 0.01 gms. Cellulose 0.2 gms. Agar 1.5 gms. Filtered rabbit caecal f l u i d 20 ml. Dis t i l l e d water to 100 ml. Preparation: (1) Autoclave constituents, less 20 ml. of d i s t i l l e d water and sodium bicarbonate at 120°C. for 15 minutes. (2) Seitz f i l t e r sodium bicarbonate i n 20 ml. d i s t i l l e d water. (3) Combine two solutions after cooling and make up the tot a l volume to 100 ml. with cold s t e r i l e d i s t i l l e d water. (4) Dispense Medium using st e r i l e technique into sterile screw-capped tubes i n 6 ml., 15 ml., and 20 ml. lots. TABLE XIX Anaerobic Agar Medium k, Modification of B.B.L. Thyoglycollate Medium (Brewer-modified) CONSTITUENT AMOUNT Thi oglyc ollat e medium(B.B.L.) Brewer modified Agar Cellulose Stock salt solution 4 D i s t i l l e d water 30 gms. 1.5 gms. 0.5 gms. 10 ml. to 1000 ml. -33. -TABLE XLX - cont'd Preparation: (1) Mix and l e t stand five minutes. (2) Dissolve by bringing to the b o i l . (3) Dispense in test tubes in 15 ml. and 20 ml. lots. (4) Autoclave at 120°C. for 15 minutes. TABLE XX Stock Salt Solution 4 CONSTITUENT AMOUNT Sodium chloride 25 gms. Potassium chloride 2 gms. Calcium chloride 1 gm. Dis t i l l e d water to 100 ml. Aerobic media were also used i n the bacteriological study; these included nutrient broth (Beef Heart Infusion broth) and diff e r e n t i a l carbohydrate media. The sugars used were dextrose, xylose, and inulin. Cellulose in the form of Cellulose Gum (Sodium carboxymethyl cellulose, Hercules Powder Co.), cellibiose and Soluble Starch (Fisher) were also included in the dif f e r e n t i a l carbohydrate media. A l l carbo-hydrate media were prepared as given i n Table XXI. Also used were MacConkey Agar which inhibits growth of gram positive organisms and i s used primarily for enteric pathogens, and S.S. Agar which i s a selective enteric medium for the Salmonella Shigella group. TABLE XXI Differential Sugar Medium, Peptone water CONSTITUENT AMOUNT Proteose peptone No. 2(Difco) Stock salt solution 4 Di s t i l l e d water 1 gm. 1 ml. to 100 ml. - 34 -TABLE XXI - cont'd  Preparation: ( 1 ) Heat ingredients completely and adjust volume. ( 2 ) Adjust pH to 7 . 1 . ( 3 ) Add 0 . 1 ml. of a 1 . 6 per cent alcoholic solution of brom cresol purple. ( 4 ) Autoclave at 120°C. for 2 0 minutes i n 1 0 0 ml. lots. ( 5 ) Add sugars at rate of 0 . 5 per cent. ( 6 ) Dispense i n test tubes, with gas tubes, i n 1 5 ml. lots and reautoclave. E. A r t i f i c i a l Caeca: Caecal contents of both beaver and rabbit were mixed with peptone water (Table XX). One hundred ml. of peptone water was added to the entire caecal contents. This material was used immediately, or 5 0 ml. aliquots were fast frozen in large mouthed screw-capped vials for use at specified time intervals. The a r t i f i c i a l caeca consisted of test tubes measuring 2 0 0 mm. by 2 5 mm. A piece of rolled parchment paper, two inches square was inserted into each test tube. A rubber balloon was attached to the mouth of each tube to collect any gases formed during fermentation. The given experimental technique i s the procedure used by Ebbett ( 1 9 5 6 ) with the exception of the Peptone water. In the investigation carried out by Ebbett ( 1 9 5 6 ) a buffering solution as given in Table XIII was used. Rumen material used i n other in vitro studies was more f l u i d than the caecal contents of the beaver. Peptone water was added to produce a more f l u i d material. - 35 -METHODS A. Bacteriological Study 1. Housing of Experimental Animals (Beaver) Pens or holding tanks were constructed by Stephenson (1956) for beaver experimental work. The pens consist of a metal trough f i l l e d with water, a feeding platform at one end and an enclosed den at the other. The trough, made of galvanized metal, i s ten feet long, three feet wide, and two and a half feet deep. Inside dimensions of the dens are three feet long, two and a half feet wide, and two feet high. There i s a hole fourteen inches i n diameter in the floor of the den leading via a sloped walk into the tank. The feeding platform has the same floor area as the den, arid i s accessible up a sloped plank. The platform i s covered with wire mesh because of the beaver's habit of chewing. Water i s supplied by hose. There i s an overflow hole but i t was found easier to f i l l the tank to 18 inches only. Tanks were cleaned approximately once a week. Feeding dishes, 12 inches by 7 inches, by 4 inches, were fixed to the feeding platform. 2. K i l l i n g and Post Mortem Technique Beaver were k i l l e d with an overdose (more than 1.5 ml. per pound of body weight) of Veterinary Nembutal (Abbott), (60 mg. per ml. of solution), injected intraperitoneaLly. Rabbits used i n this study were sacrificed with a saturated solution of magnesium sulfate injected intravenously. Post mortem examinations were carried out as aseptically as possible. Animals were skinned and then stretched out on a clean table. Muscle tissue was disinfected with 70 per cent alcohol. A midline incision was made into the peritoneal cavity. The digestive tract was then removed - 36 -using sterile instruments. Great care was taken to remove the entire gastro-intestinal tract without tearing. The caecum was ligated and removed for further study. The digestive tract minus the caecum was cut open and a visual description of the contents recorded. 3• Microbiological Study of the Caecum Several methods of studying the bacteriological flora of the caecum were used with a varying degree of success. The f i r s t method employed was a modification of the techniques of Hungate (1950) and Doetsch et a l . (1952) to culture rumen bacteria. Dilution blanks were prepared (Table XII) from 10~1 to 10"^ using st e r i l e technique. Ten ml. of caecal contents were added to 90 ml. of the dilution medium to produce the f i r s t dilution. Caecal material from both the beaver and the rabbit were set up i n thi s manner. Following the inoculation with caecal material the resulting dilutions were gassed for two minutes with carbon dioxide. Che ml. of dilutions 10"7 to 10" 1 0 was added to six ml. of melted cooled agar medium. Media given i n Tables XIV, XV and XVIII were used. The samples were mixed under carbon dioxide i n screw-capped v i a l s , to retain anaerobiosis. Agar was s o l i d i f i e d i n a thin f i l m on the walls of the test tube by rotating under cold water. The tubes were incubated at 37°C for 24 to 48 hours. One ml. of dilutions 10~^ to 10~9 w a s added to 20 ml. of melted cooled agar.medium (Tables XV and XVIII). Four plates were prepared and incubation carried out for 12, 24 and 36 hours at 37°C. Counts were made of a l l visible colonies at given time intervals. Incubation was carried out both aerobically and anaerobically. - 37 -One ml. of caecal f l u i d was inoculated directly into 20 ml. portions of the four agar media used (Tables XIV, XV, XVIII and XIX). These shake cultures were prepared as pour plates and incubated at 37° C. aerobically and anaerobically t i l l colony formation appeared. Anaerobiosis was produced by carbon dioxide. Thioglycollate medium (Table XIX), S.S. Agar, and MacConkey Agar (B.B.L.) were prepared as sterile plates. These plates were streaked with caecal contents and incubated aerobically and anaero-bi c a l l y . Isolated colonies were cultured i n Thioclycollate Medium (B.B.L.) and after 24 hours incubation at 37°C. were streaked on to the three types of agar given above. A l l organisms were subcultured aerobically and anaerobically. Agar slopes were prepared using media as given i n Tables XVIII and XIX. Stabs were made on these slopes using caecal contents as inoculum. These test tubes were incubated at 37°C. aerobically and anaerobically. A l l isolated cultures were inoculated into carbohydrate media and incubated aerobically. Cellulose and cellobiose media were also incubated anaerobically. Most of the bacteriological investigation was carried out using fresh caecal contents. However, as c e l l u l o l y t i c activity was shown i n frozen samples of beaver caecal contents, bacteriological study was also carried out on frozen samples. Caecal contents mixed - 38 -with peptone water (Table XXI) was frozen i n 5 0 ml. lots. These samples were thawed, prior to use, by immersion i n warm water and then inoculated into Thioglycollate Medium (B.B.L.). A l l growth was cultured and subcultured bn to agar media (Table XYIII, S.S. . Agar, MacConkey Agar). 4(a) A r t i f i c i a l Caeca, i n vitro study Caecal contents, diluted to pouring consistency with peptone water (Table XXI), was poured into test tubes, 2 0 0 mm. by 2 5 mm. to a depth of three inches. Each test tube contained a piece of rolled cellulose paper, two inches square. The tubes were sealed by f i t t i n g a balloon over the mouth of each tube. The tubes were incubated in a water bath at 37°C. to 3 9 GC. for definite time intervals. Controls were set up using cellulose paper i n peptone water. Beaver and rabbit caecal contents were both used in this study. Frozen caecal contents from both beaver and rabbit were used; mixture was frozen for given time periods. (b) Caeca, in vivo study A number of rabbits were subjected to surgery i n an attempt to find out i f particles of parchment paper placed into the caecum would be digested at the same rate as paper in a r t i f i c i a l caeca. The rabbits were anesthetized with Veterinary Nembutal (Abbott) (60 mg. per ml.), at the rate of one cubic centimeter per five pounds body weight. The animals were stretched out on a sterile table and the abdominal area shaved. An incision was made into the abdominal cavity to the right of the midline through skin and muscle tissue. The large curve of the caecum was drawn up into the incision and a small hole cut through the muscle coat. A piece of parchment paper two inches long by half an inch wide was rolled longitudinally and inserted through the small opening. Each piece of paper had a length of cotton thread stitched through one end; this was used to anchor the paper to the caecal wall for ease i n recovery. The caecum was repaired with a double purse-string suture and the skin stitched with interrupted sutures. The animals were fed for specified time intervals, 24 hours, 36 hours, and 48 hours. Several methods of inserting the parchment paper were tried before the stated method was decided upon. The parchment paper i n early experiments was not attached to the caecal wall, just inserted free i n the caecum. Later a small glass tube with holes in the walls was used, the paper put into the tube and the tube then inserted into the caecum. Results from these methods were unsatisfactory. It was found more efficient to fasten the paper to the muscle wall of the caecum with a long thread. Rabbits were sacrificed at specified time intervals and the differences in weight of the parchment paper calculated. The results of these experiments were satisfactory. One beaver was subjected to similar treatment. However, the effect on the animal was so unsatisfactory that i t was decided not to continue this part of the experiment. With animals more adaptable to handling and pen feeding this experimental technique might give interesting results. B. Digestibility Study: 1. Housing and Feeding of the Beaver Two beaver were used i n this part of the study. These beaver were kept i n the tanks u n t i l such time as they were moved to the main building. The room used was seven foot by six foot, with a cement floor sloping to a drain at the back. This room fac i l i t a t e d the collection of uncontaminated fecal material. Marked feed (Table XI) with one per cent chromic oxide, was fed to the two animals, numbered Beaver 8 and Beaver 9« Beaver 8 was fed marked feed for three days prior to removal from the tank. Stephenson (1954) stated that 60 hours was required for food passage i n the beaver. To permit some leeway a 72-hour interval was allowed for time of food passage. Marked feed was continued after moving the animals to the observation room. Beaver 8 lived i n the observation room four days before any fecal material was passed. After this time the animal appeared to settle down and fecal material was passed regularly every 24 hours. Beaver 9 was moved from the tanks and exchanged with Beaver 8 after two weeks. The animal was more d i f f i c u l t to handle and did not rea l l y settle d own in the observation room. Fecal passage starred after four days i n scant amounts and then ceased for a 24-hour period. The amounts of fecal material passed for the next twelve days was variable. Two rabbits, designated as 1 and 2, were also fed marked feed. The rabbits were kept i n wire cages with a grid under them to collect the fecal material passed. Feed was provided as a mass mixed with water. - 41 -Water was also fed ad libiturn. Feed was changed every day when fecal collections were taken. 2. Marker Determination A standard curve was prepared using the Beckman Model DU Spectrophotometer (Schurch et a l . 1950) for chromic oxide. Known amounts of chromic oxide were dried i n an oven for one hour at 600°C, i n a 75 mgm. nickel crucible. After cooling, one gm. of sodium peroxide was added and the mixture heated to a flux over a bunsen burner. This flux was returned to the oven at 600°C. for five minutes. The crucibles were cooled and then f i l l e d with d i s t i l l e d water. The mixture was allowed to stand for ten minutes. The contents were poured into a 500 ml. beaker and the crucible washed three times with hot d i s t i l l e d water. This mixture was allowed to stand for 30 minutes; and was then f i l t e r e d through a No. 1 Whitman f i l t e r into a 500 ml. erlenmeyer flask. The residue was washed with warm water. The solution was made up to 500 ml. i n a volumeteric flask with d i s t i l l e d water. A l l solutions were read at a lig h t transmission of 440 mu. and a s l i t width of 0.02 mm. The standard curve was drawn plotting optical density against mgms. of chromic oxide (Figure l ) . Feed and fecal samples were dried i n an oven at 100°C. or less and then ground i n an Arthur H. Thomas Co. grinder using a No. 20 screen. These samples were stored i n air-tight bottles. One gm. of each of these samples was subjected to the same treatment as the pure chromic oxide. Optical density was calculated for each sample and the mgms. of chromic oxide per gm. of feed or feces read off the standard curve. Feed samples were taken from the feed container prior to feeding and from the feed dish at varying intervals. Fecal samples were collected for two weeks for the - 43 -beaver and rabbits and five days for the mink. 3• Cellulose Determination Cellulose i n the feed and feces was determined using the method of Crampton and Maynard (1938). One gm. of the ground material as prepared for the colorimeteric determinations was used, and was placed i n a 125 ml. round flask. Fifteen ml. of 80 per cent acetic acid and 1.5 ml. concentrated n i t r i c acid were added and the mixture swirled to suspend a l l the dry material. The mixture was refluxed for 20 minutes. The mixture was transferred to a centrifuge tube, 50 ml. volume, and the flask rinsed twice with 95 per cent ethyl alcohol, which was added to the material i n the centrifuge tube, about 15 ml. of alcohol was used. After the material was centrifuged for ten minutes in a MSE centrifuge, the f l u i d was decanted and the residue washed twice in 95 per cent ethyl alcohol at the same speed as before. The material plus the last washing of alcohol was transferred to a porcelain crucible. The residue was washed twice with hot benzene, twice with hot alcohol, and twice with ether under suction. The crucible was dried and weighed. The material was ignited at 600°C. for two hours, then cooled and weighed. The change i n weight was taken as the amount of cellulose present i n the original sample. 4. Apparent Digestibility Substitution of the chromic oxide values in the following equation allows the determination of the apparent digestion coefficient for cellulose in the dry material without a knowledge of the total quantity of feces produced or feed consumed. This follows the formula of Reid et a l . (1950) for chromogens as an indication of d i g e s t i b i l i t y . Apparent - 44 -d i g e s t i b i l i t y i s equal to 100 - (100 a.x. i n feces), where x eqauls b.x. i n feed the per cent of cellulose, a equals the amount of chromic oxide per gm. of feed, b equals the amount of chromic oxide per gm. of feces. Apparent di g e s t i b i l i t y was calculated for cellulose i n Beaver 8 for ten consecutive days, in Beaver 9 for 14 days, Rabbit 1 and 2 for 14 days, and the mink for nine days. RESULTS AND DISCUSSION A. Experimental Animals; The beaver used in this study were a diversified group. A ir f l i g h t and handling following capture, coupled with being placed i n confined quarters tended to put the animals off feed. Strange food added to the stress syndrome. Some of the animals used had been subject to other experimental techniques, as for example, the blood chemistry study of Stephenson, (1956). To find i f any pathological changes were produced by either the inappetence following capture, or the hematology experiments, a careful post mortem examination of each animal was made. The five digestive tracts obtained from Ontario were used for comparison. These specimens were assumed to be normal as the five animals were dead-trapped and could be considered as interrupted in their normal l i f e . The animals from Vancouver Island were numbered i n the order of their ar r i v a l and sacrifice. The specimens from Ontario carried numbered tags and these numbers are used where reference i s made to these animals. A brief description i s given of each animal with any obvious pathological changes. Beaver 1, i n captivity at start of experiment, was not in good health; post mortem examination revealed extensive chronic inflammatory areas on heart and aorta. Beaver 2, i n captivity at start of experiment, was in poor health; showing evidence of cardiac insufficiency. There was heart damage vi s i b l e on post mortem. - 46 " Beaver 3 was i n tanks for four months prior to sacrifice. Animal was lethargic and refused food; showed no post mortem lesions. Beaver 4 was held for three days prior to sacrifice, during which time i t did not eat. Beaver 5 was trapped at the same time as Beaver 4 and was kept for two weeks prior to sacrifice, did not eat. Beaver 6, kept just over one month, was sacrificed when i t stopped eating. Beaver 7 was kept 24 hours i n isolation on a dry floor following a r r i v a l at U.B.C. It was then sacrificed. Beaver 8 and 9 were used i n directed food study and not sacrificed, appeared healthy. Beaver 10 died of starvation during the course of experiment. Post mortem showed an empty digestive tract with advanced necrosis of caecal wall. Beaver 11 was kept as a spare for directed food study, appeared healthy. Beaver 4284, 4288, 4451, 4452, and 4522 were digestive tracts from Ontario. B. Macroscopic Study: Table XXII gives the contents of each section of the gastro-intestinal tract of the beaver under study. There i s a marked difference i n the two groups, the captive and the dead-trapped. Without exception the stomach, duodenum, and jejunum of the captive beaver were empty; and the - 47 ~ TABLE ZXII Macroscopic Appearance of Material i n Digestive Tract of Beaver ANIMAL STOMACH SMALL BIT. LARGE INT. CAECUM RECTUM 1 Empty- Duodenum empty, jejunum empty, ileum green material semi-solid Green semi-solid material Thick green material, semi-liquid i n apex Yellow material 2 Empty Empty Empty Wood shavings paper thin 2 inches, by 1/8 inches, f l u i d i n apex Yellow material 3 Empty As 1 As 1 As 1 As 1 4 Empty As 1 As 1 As 1 As 1 5 Empty Duodenum empty, Empty Stichorchis Fluid only wall covered Pale mucoid jejunum empty, ileum empty Stichorchis present Stichorchis subtriquetrus material ^present 6 Empty As 1 As 1 As 1 As 1 7 Empty As 1 As 1 As 1 As 1 10 Empty Travassosius Empty Empty ' Empty Paramphastomum Empty rufus present castori present 4284 4288 4451 4452 Full ground material, bits of wood Contained moist material finely ground Dry material roughage as i n stomach soft part lacking Very f u l l more moist, most f l u i d at apex Material dry semi-pelleted 4522 -'48 -ileum, large intestine and caecum i n most instances were f u l l . The dead-trapped animals had a digestive tract f u l l of material which looked similar from stomach to rectum. The dead-trapped animals obviously ate more by volume than the captive animals. There are several possible explanations for this apparent variation i n food intake. The variation could be due to; palatability of food material, "nutritional wisdom", nutritional requirements of the animals, stress, and pathological changes i n the animals. Each of these factors i s discussed briefly. Nutritionists disagree as to the importance of palatability in feeding studies. Some workers contend that palatability influences the type and the amount of food eaten; whereas others argue that i s i s an unimportant factor. In the wild, animals certainly do show discrimination i n the materials which they eat. The amount consumed of an unpalatable food material i s less than that of a preferred food stuff. Beavers l i v e where there i s water and appropriate food, moving out to another area when a l l the trees are cut. Wild l i f e management studies show that one of the factors limiting the range of animals i s the av a i l a b i l i t y of certain food materials; with domestication palatability i s a less decisive factor. An animal can be 'taught' to eat the food available. The level of intake would probably be lower with an unpalatable ration than with a palatable ration. The ration fed to the captive beaver may have been unpalatable and the feed intake therefore less than that of natural diet. Beaver 2 refused to eat the pellets and ate the bark and gnawed the wood of the branches provided. "Nutritional Wisdom", a term used by Brody (1945), can be taken to mean that animals eat the food material which w i l l best supply the needs of the body for growth and maintenance. It i s a term related to the energy - 4 9 ~ content of the diet. Dove ( 1 9 4 3 ) stated that rabbits prefer succulent foods with the highest moisture content and the lowest fiber content. High moisture and low fiber content are correlated to physiological immaturity and associated with high d i g e s t i b i l i t y , and high vitamin-mineral content.. The rabbit demonstrates "nutritional wisdom" by preferring this type of food material. Ration 16-57 (Table XI), i s balanced according to nutritional concepts and i s lower in fiber and higher in protein by volume than twigs and bark. The beaver could be exhibiting "nutritional wisdom" in not eating as much by volume. A l l the nutritive factors necessary for growth and maintenance are available in a smaller volume of food material. The level of blood sugar i s a factor i l l u s t r a t i n g the relation between nutritive requirements and food intake. Ration 16-57 (Table XI) being more highly concentrated than the natural food material would satisfy the blood sugar level with lower volume intake. Stress i s used here to refer to nervous tension and any accompanying physiological reaction resulting from changes in the normal environment of the animal. Inappetence was the response seen in the animals used i n this experiment. Some of the beaver rapidly became acclimatized to the tanks, and ate the food provided. Other animals, beaver 1 0 especially, gave up eating for two days after the water was changed in the tanks. In the direct feeding study beaver 8 ate well after a short period of active fear; beaver 9 never settled down, demonstrating a variable feed intake and diarrhoea. Stress i s a variable factor and did not affect a l l the animals to the same degree. It i s unlikely that this factor produced the consistent lower volume of food eaten in captivity. -50-Pathological changes as encountered i n the present investigation, would seemingly, not in themselves produce a lowered food intake, though the cardiac insufficiency produced by the heart lesions and giving rise to lethargy, could have lowered the food intake in beavers 1 and 2. In beaver 10 i t i s d i f f i c u l t to say whether the necrosis of the caecal wall was caused by, or was produced by the stoppage of food intake. The other beaver which showed neither pathological heart lesions nor caecal changes, had digestive tracts as empty as the diseased animals. It cannot be said with any definite proof that pathological changes caused a decreased food intake i n any one animal. The exact cause for the decreased food intake i n the captive animals i s impossible to state, but a l l factors must be considered to affect each animal to a different degree. Ration 16-57 (Table XI) i s the standard diet fed to the rabbits i n Central Animal Depot, U.B.C. In an attempt to judge this ration for the beaver, rabbits sacrificed for other experiments were observed. The animals which had been raised on Ration 16-57 plus grass and remained on this diet throughout l i f e , had digestive tracts f u l l of feed from stomach to rectum, as had beavers 4284, 4288, 4451, 4452 and 4522. There were some workers feeding high fat diets and with their kind permission the intestinal tracts of these experimental rabbits were also observed; this diet was atypical for the animals observed. The digestive tracts of these rabbits were as beaver 1 and 2 with only the caecum f u l l of feed. Lower food intake was observed and i s obviously a factor to be considered i n any change of diet i n the rabbit. Rabbits fed restricted amounts of Ration 16-57 also had half empty digestive tracts. The above observations emphasize the fact that care must be taken in interpreting the results of investigations "51-i n which animals have been maintained Tinder restricted and experimental conditions. C. Microbiological Study No cellulose digesting bacteria were isolated at any time during the experiment. Indication of c e l l u l o l y t i c activity was obtained i n one dilution blank inoculated with rabbit caecal f l u i d at the 10~4 level. The media used successfully by Hungate (1950, Doetsch et a l . (1952) and Hall (1952) did not appear to be compatible with the growth of c e l l u l o l y t i c bacteria from the caecum of the beaver. Rumen f l u i d was used i n the media. Hall (1952) cultured a c e l l u l o l y t i c cocci from the caecum of the rabbit using both rumen f l u i d medium and caecal f l u i d medium. It i s d i f f i c u l t to say i f beaver caecal f l u i d would have been a better growth factor. There i s l i t t l e free f l u i d in the caecum of the beaver, and the number of animals available was not inducive to the use of this material i n the manufacture of media. Direct smears of digestive contents were made. These smears demonstrated the presence of gram negative and positive rods, gram negative and positive cocci, and large numbers of a spirochaete. Plate counts were made and gave a colonial count of between 3 x 10^ and 4 x 10^ organisms per ml. of caecal contents. These figures do not compare with the colony counts given i n the literature for the ruminant. The number of rumen organisms counted by Johnson et a l . (1944) using aerobic medium i s recorded as 6.5 x 10 6 organisms per ml. The colony count given by Hall (1952), of c e l l u l o l y t i c cocci from the caecum of the rabbit i s 25 - 72 x 10° per gm. moist caecal contents. Bryant and Burkey (1953b) give a range of 1.8 x 109 to 6.5 x 109 organisms per ml. of rumen contents. - 52 -The difference in numbers occurred on different diets. A medium which i s compatible to the growth of bacteria i s a prerequisite of satisfactory colony counts. The media used i n this study was not satisfactory. There-fore the number of organisms or colonies recorded must be considered as low. A l l organisms grown, with one exception^ were facultative anaerobes of the coliform group. TablesXXI, XXII, and XXIII l i s t a few of the organisms cultured and some of the results obtained on differential media. Obligate anaerobiosis i s mentioned by Hungate (1950)«.Gall et a l . (1951) and Hall (1952) as being a criterion of natural rumen or caecal bacteria, especially one which would digest cellulose. The coliform group was cultured from a l l animals and could therefore be considered as natural. This group of organism might have been a contaminant from the tanks which were a common denominator to a l l animals except beaver 7. One organism cultured was an obligate anaerobe. This gram positive rod occurred morphologically i n short chains or single rods. No growth could be obtained on any carbohydrate media. The colony formation was a small, white, firm, round growth on anaerobic medium No. 4 (Table XIX). The organism was obtained from one animal, beaver 6, and was visible on several direct inoculations on prepared plates of medium No. 4. No c e l l u l o l y t i c action was observed. The discrepancy between the number of organisms seen on direct smear and those obtained on culture i s great since obligate anaerobes are d i f f i c u l t to culture on known medium. In this study there i s the problem of the s u i t a b i l i t y of the media for the organisms present. Inability to culture cellulose digesting organisms from the rabbit on medium successfully employed by Hall (1952) for a similar study points to the failure as being a technical one. - 53 -Early studies carried out on rabbits on a barley diet failed to demonstrate cellulose digesting bacteria (Hall, 1952). Diet does affect the number of bacteria i n the-rabbit caecum (Hall, 1952). The change in diet of the beaver may have been pa r t i a l l y responsible for the failure to culture cellulose digesting bacteria from the beaver caecum. There were however many organisms present which did not grow on culture media and any one of these might have been cellu l o l y t i c on compatible medium. D. A r t i f i c i a l Caeca: A r t i f i c i a l caeca were prepared using the caecal contents of both beaver and rabbit as inoculum. The entire contents of the caecum was added to the dilution material (Table XXI). Parchment paper was included as a measurable source of cellulose. There was cellulose material included in the inoculum. No record was kept of the weight of this material. The caeca could have been prepared using f i l t e r e d caecal contents and this would have eliminated one unknown, that i s , the amount of cellulose i n the inoculum digested i n the a r t i f i c i a l caeca. The amount of digestion given i n Table XXVI i s the change in weight of the parchment paper during a specified time interval. The control values show that parchment paper exposed to a salt solution and a warm temperature loses a small percentage of i t s weight. For this experiment the loss of weight i n the control tubes i s a r b i t r a r i l y taken to cancel out the digestion of cellulose in the inoculum. It i s probable that the amount of the digestion of cellulose i n the inoculum was greater than the weight loss of the paper. The bacteria undoubtedly adhere to the particles of food material i n the caecum, and a l l would not be shaken loose by the agitation, therefore digestion would continue on the fibrous material included i n the inoculum. - 54" TABLE XXIII Growth Characteristics of Some Caecal Bacteria from the Beaver MORPHOLOGY GRAM REACTION GELATINE LIQUE-FACTION GLUCOSE SUCROSE LACTOSE INULBI Rod short chained — — A A 0 0 Cocci paired - - AG AG AG 0 Rod chain - - A 0 0 A Rod single - - AG • A A A Rod single - - A 0 0 A Rod long chain - - A A A TABLE XXIV Dextrose and Cellobiose Reaction of Some Caecal Bacteria from the Beaver MORPHOLOGY GRAM REACTION DEXTROSE CELLOBIOSE Rod - AG AG Rod - AG AG Rod - AG 0 Rod + A 0 TABLE XXV Carbohydrate Reaction of Some Caecal Bacteria from the Beaver MORPHOLOGY GRAM REACTION DEXTROSE XYLOSE INULTN Rod AG AG 0 Rod - AG 0 0 Rod - A 0 0 Rod - AG A 0 Rod - AG AG AG Rod - A A 0 x A - produce acid - negative G - produce gas + positive AG - produce acid and gas 0 - no reaction The rabbit demonstrated a digestion of up to 20 per cent of the available cellulose in a r t i f i c i a l caeca inoculated with fresh caecal contents (Table XXVI). Hall (1952) demonstrated that rabbits on a diet of cracked barley digested no cellulose while those on a diet of cracked barley plus f i l t e r paper digested 24 to 34 per cent of the available cellulose. The horse i s considered to digest 21 to 57 per cent of the available cellulose (in Sijpesteijn, 1948). In the present experiment the caecal contents of the beaver demonstrated (Table XXV) a digestion of 31.3 per cent of the available cellulose i n 108 hours. In the guinea pig the digestive tract i s so constructed that the food goes directly into the caecum where churning takes place (Alvarez et a l . , 1918). In the rabbit Alvarez et a l . (1918) believe that some of the food goes into the caecum, some into the colon. In the caecum, muscle action i s such as to cause churning of the contents. The churning would produce not only mixing of the contents of the caecum but distribution of the bacteria. Long chain organisms would be broken and dispersed more thoroughly through the food. Food remains i n the caecum many days. A factor, which might have increased the c e l l u l o l y t i c activity i n the a r t i f i c i a l caeca would be constant agitation. The tubes were shaken three times over a 24-hour period, but this could i n no way be considered equal to the churning of the caecum i t s e l f . Rabbit 1 demonstrated the highest percentage of digestion of any of the eight rabbits used. This value was at most 20 per cent. There i s an indication that time i s a factor influencing the extent of cellulose digestion. The time factor may be related to the population of bacteria and the normal growth rate of that population. Cellulolytic bacteria i n the ruminant were shown by Gall et a l . (1951) to be slower growing than - 36 ~ organisms which digest glucose or soluble carbohydrates. The break-down of cellulose may i t s e l f take time. Rabbit 2 could be said to demonstrate no digestion of cellulose. The control tubes lost 1.8 to 6.6 per cent of the cellulose} this series of caeca lost 1.9 to 9.9 per cent of the cellulose. The loss i s small and could be considered insignificant. Because of an abnormal circulatory system the general health of beaver 1 was not good. Digestion of cellulose by this animal's caecal contents was non-existent. Materials from the caeca of beaver 3 and 6 were prepared as a r t i f i c i a l caeca. The results obtained were similar to beaver 1 and for that reason not included. Digestion of cellulose was not visible i n these animals i n significant amounts. Beaver 7, never i n the tanks, was sacrificed 24 hours after capture. The digestion of cellulose was slow i n starting but reached the le v e l of 31 per cent of the measurable cellulose i n 108 hours. At this time i t appeared that the peak of digestion had been reached. Mo attempt was made to maintain a suitable pH in the tubes. There may have been at this time an accumulation of fatty acids from digestion at a level high enough to stop further digestion due to an acid and therefore unfavourable environment. The values obtained using caecal material frozen for definite time periods demonstrates an increase in c e l l u l o l y t i c a c t i v i t y after 48 hours of freezing. Rabbit 3 showed no increase i n digestion of cellulose after caecal material had been frozen 24 hours and values were close to those obtained with fresh caecal material. Caecal material from rabbit 4 demonstrates up to 59-3 per cent digestion of measurable cellulose - -57-TABLE XXVI Some Results Obtained Using A r t i f i c i a l Caeca to Demonstrate Cellulose Digestion ANIMAL PAPER "WT. GMS. TIME IN WATER BATH HOURS SALVAGE WT. OF PAPER GMS. CHANGE IN PAPER WT. MGMS. PER CENT DIGESTION Rabbit 1 0.1522 24 0.1429 - 9.3 6.1 0.1545 48 0.1390 -15.5 10.3 0.1572 72 0.1381 -19.1 12.2 0.1526 96 0.1327 -19.9 13.0 0.1552 120 0.1248 -30.4 19-6 Rabbit 2 0.1543 24 0.1513 - 3.0 1.9 0.1565 48 0.1520 - 4.5 2.9 0.1508 72 0.1358 -15.0 9.9 0.1559 96 0.1427 -13.2 8,5 -. 0.1499 120 0.1370 -12.9 8.6 Beaver 1 0.1615 24 0.1600 - 1.4 0.9 0.1565 48 0.1530 - 3.5 2.2 0.1557 72 0.1520 - 3.7 2.4 0.1500 120 0.1535 - 3.5 -Beaver 7 0.1554 12 0.1575 - 2.1 -0.1570 . 24 0.1611 - 4.1 -0.1524 36 0.1528 - 0.4 -0.1523 48 0.1525 - 0.2 -0.1542 60 0.1464 - 7.8 5.1 0.1544 72 0.1400 -14.4 9.3F 0.1523 84 0.1283 -24.0 15.8 0.1551 96 0.1230 -32.1 20.7 0.1524 108 0.1047 -47.7 31.3 0.1532 120 0.1160 -37.2 24.3 0.1546 120 0.1385 -26.1 16.9Q TABLE XXVI - cont'd ANIMAL PAPER WT. GMS. TIME IN WATER BATH HOURS SALVAGE WT. OF PAPER GMS. CHANGE IN PAPER WT. MGMS. ,, PER CENT DIGESTION Beaver 7 0.1556 132 0.1217 -33.9 21.8 L 0.1530 144 0.1155 -37-5 24.5 M Control 0.1486 24 0.1432 - 5.4 3.6 0,1480 48 0.1444 - 3.6 2.4 X 2 0.1470 72 0.1398 - 7.2 4-9' 0.1511 96 0.1412 - 9.9 6.6 0.1458 130 0.1432 - 2.6 1.8 Rabbit 3 0.1543 24 0.1513 - 3.0 1.9 frozen 24 hours 0.1565 48 0.1520 - 4.5 2.9 0.1508 72 0.1358 -15.0 9.9 l c 0.1559 96 0.1427 -13.2 8.5 0.1499 102 0.1370 -12.9 8.9 Rabbit 4 0.1569 24 0.1520 - 4.9 3.1 frozen 48 hours 0.1496 48 0.1348 -14.8 9.9 0.1483 72 0.1213 -27.0 18.2 0.1557 96:. : 021212 .-34.5 22.2 0.1567 120 0.0637 -93.0 . 59.3 Rabbit 5 0.1518 24 0.1381 -13.7 9.0 frozen 72 hours 0.1490 48 0.1342 -14.8 9.9 0.1567 72 0.1391 -17.6 11.2 0.1577 96 0.1337 -24.0 15.2 0.1622 130 0.1373 -24.9 15-4 - 59 " TABLE XXVI - Cont'd ANIMAL PAPER WT. . GMS. TIME TN WATER BATH HOURS SALVAGE WT. OF PAPER GMS. CHANGE IN PAPER WT. MGMS. PER CENT DIGESTION 1 Beaver 7 0.1560 5 days 0.1356 -20.4 13.1 frozen 9 days 0.1547 5 days 0.1356 -23.1 14.9 0.1536 5 days 0.1235 -30.1 19.6 0.1546 5 days 0.1385 -16.1 10.4 0.1534 5 days 0.1242 -29-2 19.0 0.1530 5 days 0.1327 -20.3 13-3 - 6 0 -following a 48-hour period of freezing. Freezing may k i l l or inhibit organisms which slowed or retarded the bacteria with c e l l u l o l y t i c activity. Freezing to 72 hours did not improve cel l u l o l y t i c activity. The bacteria were s t i l l viable after 72 hours, demonstrating a digestion of 15 per cent of the measurable cellulose in the a r t i f i c i a l caeca. Caecal material frozen nine days demonstrated no increase i n ce l l u l o l y t i c activity. The highest value obtained was 20 per cent. This was not as high as the value of 31 per cent from fresh material. This experiment did demonstrate that the ce l l u l o l y t i c bacteria from the beaver caecum can withstand freezing for at least nine days. Five days i n the water bath did not change the end point of digestion; 96 to 108 hours appeared optimal. Beaver 7 was not fed Ration 16-57 (Table XI), being sacrificed within 24 hours of capture. Digestion to 31 per cent of the measurable cellulose was demonstrated. Bacteria are very specialized in their food requirements and Ration 16-57 may be incompatible with the continued growth of the resident c e l l u l o l y t i c bacteria of the beaver caecum. Many other workers have shown that diet influences the bacterial endoflora and the digestion of cellulose by herbivores. For instance, diets high in grain cause a decrease i n the number of rumen bacteria end protozoa (Gall et al«, 1951); the flora changing from slow growing to fast growing organisms. Using a r t i f i c i a l caeca, Kuhtanen et a l . (1954) demonstrated; good digestion by bacterial flora of the rumen on the cellulose i n high fiber diets, and poor digestion i n diets with more soluble carbohydrates present such as starch and lactose. Supplements containing soluble sugars tend to depress the d i g e s t i b i l i t y of the fibrous part of the diet (Johnson et a l . , 1944). From the figures l i s t e d i n the literature survey i t w i l l be noted that Cellulose Paper Recovered from A r t i f i c i a l Caeca plants normally eaten by the beaver contain from 15 to 40 per cent fiber as opposed to the food fed, (Table XII), which contained 6 to 7 per cent crude fiber as cellulose. Figure 2 demonstrates areas where the cellulose-digesting bacteria have eroded the surface of the parchment paper which was inserted into the a r t i f i c i a l caeca. Reference to Table XXV w i l l give the exact weight losses of the paper. In the control X2 the parchment paper retained i t s shiny surface. The example from the rabbit experiment, l c , was not rolled as tightly as the papers used in the beaver a r t i f i c i a l caeca and the entire surface has been eroded. The four samples from the beaver caeca, F, L, M, Q, demonstrate areas of erosion and areas untouched. The paper was folded over to keep i n a r o l l . Careful examination of Figure 2 shows that the folded end i s the unaffected area of the paper. The fold marks are v isible. Smaller pieces of paper or shredded cellulose would have been more effectively digested, but large pieces of paper have an advantage i n ease of recovery. The bacteria demonstrate surface erosion only. The one tube i n the bacteriological experiment which digested cellulose demonstrated the same results. The paper held i t s shape u n t i l agitated and then i t disintegrated indicating surface erosion. E. Digestibility Study; Digestibility t r i a l s constitute one method of finding the nutritive value of a certain food material. In wild animals i t i s d i f f i c u l t i f not impossible to identify the fecal output i n relation to a given intake of food. Markers are used i n time studies with feed materials, and these can give the beginning and the end of certain food passage times. This method i s used where to t a l food intake and fecal output i s known. Indigestible materials are added to the feed to give an index - 63" of d i g e s t i b i l i t y from a representative sample of food and feces rather than from t o t a l quantities of either. The indigestible material . concentrates i n the feces. Chromic oxide which i s completely indigestible i s the substance i n common use (Dansky et a l . , 1952; Mueller, 1956; Schurch et a l , 1950)• Mueller (1956) working with chickens calculated that the accuracy of the indicator method was dependent on the d i g e s t i b i l i t y of the nutrient under study and the physical character of the feed, fine or coarse ground. Finely ground feed gave increased recovery of the indicator. The difference between the true digestion coefficient and the apparent d i g e s t i b i l i t y , using indicator, may be caused by loss of indicator. This discrepancy varied or was dependent on the d i g e s t i b i l i t y of the material studied. An error caused by a loss of 10 per cent of the indicator w i l l be 9 per cent for a nutrient with a di g e s t i b i l i t y of 20 per cent, but only 2 per cent for a nutrient with a d i g e s t i b i l i t y of 80 per cent (Mueller, 1956). On an average Mueller (1956) recovered 95 per cent of the chromic oxide fed; Kane et a l . (1950) recovered 100 per cent; Dansky and H i l l (1952) recovered 95 per cent. Figures 3,4,5,6, and 7 demonstrate the daily apparent d i g e s t i b i l i t y of cellulose for the five animals studied. The actual figures are given i n the appendix. Beaver 8 (Figure 3), was fed marked feed for 4 days prior to the commencement of the feed study. The move from the tanks to the observation room caused bowel stasis for one day. The value obtained for day one of the experiment was negative. It i s estimated that this value was caused by the presence i n the digestive tracj, of unmarked cellulose. It appears to take longer than 4 days for a complete change i n intestinal - 65 -contents. Kane et al.(1950) estimated a 10-day period on marked feed was necessary for the occurrence of a static state of output being equal to intake. An apparent d i g e s t i b i l i t y of from 17 to 43 per cent of cellulose was obtained. Beaver 9 ( Figure 4) was fed marked feed for 2 weeks prior to the move to the observation room. This animal did not settle down and developed diarrhoea. The nervous disturbance of the bowel may have interfered with the digestion of nutrient, cellulose, as well as speeding up the time of food passage. This combination could give rise to the low values obtained. If this animal had remained longer on test the apparent d i g e s t i b i l i t y would probably have become more constant. Rabbit 1 (figure 5) demonstrated the necessity of a period of acclimatization. The markedly negative reading for the fourth day demonstrates a problem i n this study. At the start of the determinations for cellulose a number of test determinations were made on known amounts of cellulose. The return of cellulose varied from 75 to 83 per cent of the cellulose present at the start. The variation i s generally ignored as i t i s considered to affect both the intake value and the fecal value similarly. However, the negative value here may be a zero return as a variation between two cellulose determinations could be 8 per cent. Rabbit 2 (figure 6) had been used previously in experimental work and showed a tendency to diarrhoea. The negative values are very low and could be influenced by the experimental error i n the cellulose determinations, or the coarse quality of the feed coupled with a low di g e s t i b i l i t y of cellulose due to poor health (Mueller, 1956). Appa-re-nt d>^csti b/?<ty of^  C e l l u l o s e •Tor f?abb/t" ci over •a. fourteen d a.<j period Mink (Figure 7) do not digest cellulose. A constant negative apparent d i g e s t i b i l i t y for cellulose was demonstrated i n this study. Hall (1952) gives similar results i n rabbits fed on a diet of cracked barley, of which the cellulose fraction i s considered indigestible for these animals. Cellulose intake for the rabbit was 66 gms. and the fecal output was 82 gms. The coarse quality of the feed plus the i n d i g e s t i b i l i t y of the cellulose material i s believed to produce a high loss of chromic oxide and thus a high error and negative readings. The beaver demonstrates an apparent d i g e s t i b i l i t y of zero to 43.8 per cent of the cellulose in the diet. The negative values are lower than expected and i f caused by the combination of coarse feed and a relatively indigestible nutrient i t could be assumed that the positive values would also be low. If the values for the mink were transposed to an average of zero, the apparent digestion values for the beaver could be raised. F i <\ cire 7 f\ pp&.r-c.-n.± di^ esti bil i t<j of Cell'-'iosc. Tor H i n k 1 over a T V H « da.u period - 71 -SUMMARY AND CONCLUSIONS Twelve animals were obtained for this study which was conducted from January 1957 to August 1958. The animals were housed i n specially constructed p ens designed to provide a tank of water, feeding platform and nest box. The health of the animals which varied because of previous treatment i s considered to have influenced the results obtained. Feeding studies can be carried out more efficiently on healthy animals under relatively normal conditions. No cellulose-digesting organisms were cultured. These results were influenced by the health of the animals and the media. The media had been proved satisfactory for the culture of rumen organisms but appeared unsatisfactory for the culture of bacteria from the caecum of the beaver. An extensive study would be necessary to find a suitable medium for these bacteria. This study was a preliminary experiment to test existing techniques rather than to produce a new method of bacteriological culture. A r t i f i c i a l caeca satisfactorily demonstrate that cellulose i s digested i n the caecum of the beaver. The results obtained from healthy newly trapped animals demonstrated that foodstuff influences the rate of digestion of cellulose in the caecum. Thirty-one per cent of the measurable cellulose was digested over a period of 108 hours. This time appeared optimal for the conditions imposed by the a r t i f i c i a l caecal method used. In the animal, agitation from muscle contractions and the removal of waste products would eliminate this levelling off i n bacterial action. The bacteria act on the surface of the cellulose fibers and the larger the surface area per volume cellulose the greater the ce l l u l o l y t i c activity. The grinding of the food material to a mash, by - 7 2 -increasing the total surface area of cellulose exposed to bacterial action, increases the u t i l i z a t i o n of cellulose in the beaver. Digestibility studies with marked feed demonstrate that the beaver i s similar to the horse in i t s a b i l i t y to u t i l i z e cellulose i n the food. Comparative anatomy and per cent blood sugar levels also demonstrate a similarity between these two distinct animal types. The importance of any nutrient in the diet of an animal i s dependent on the number of Calories of energy which this material makes available. The fact that cellulose i s digested i s of interest; however, i f the digestion i s of no practical use to the animal, such as the production of energy, i t i s of l i t t l e value i n nutritional studies. Stephenson (1954) calculated that a 26-pound beaver requires 850 Calories of T.D.N, for main-tenance. The beaver i n this study demonstrated the a b i l i t y to digest 30 per cent of the available cellulose. According to Weeds and Ritman et a l . (in Sijpesteijn 1948) cellulose i s the entire crude fiber fraction of plant material, or a large percentage of this fraction. Aspen contains 28.07 per cent crude fiber (Cowan et a l . , 1950) which would give rise to 522 Calories of available energy per pound, calculating 1860 Calories per pound of carbohydrate. Given a 30 per cent d i g e s t i b i l i t y the cellulose or crude fib e r in aspen would make available to the animal 156 Calories per pound. One pound of aspen gives rise to 1165 Calories of gross energy, or estimating 50 per cent d i g e s t i b i l i t y 580 Calories of digestible energy (Stephenson, 1954). The calculated Calories i n a pound of fresh aspen increase from 580 Calories to 750 Calories with the inclusion of the supposed value for cellulose. This i s a relatively large increase and i t would appear that cellulose could be an important source of energy i n the consumption of aspen. - .73 -The above calculations are based on facts not clearly defined. The relation between cellulose and crude fiber in the nutritional f i e l d needs clarification. Cellulose i s definitely a part of the indigestible fraction in the feed of carnivores but i t i s p a r t i a l l y digested i n herbivores. The energy available from the cellulose fraction of the plant material ingested by the beaver i s not of primary importance but i t i s a factor to be considered since a food intake of 0.3 pounds of aspen would give rise to approximately 156.Calories. APPENDIX I Values obtained from Daily Feed and Fecal Study for Beaver 8 Day Per cent Cellulose Units Chromic Oxide Apparent Digestibility i n feed i n feces i n feed i n feces 1 2 Average 1 2 Average 1 6.45 26.9 26.7 26.8 . . . . 8 20.0 20.8 20.4 - 62.9 2 6.45 23-7 23-8 23-7 8 36.2 35.0 35.6 17.5 3 6.45 21.3 21.1 21.2 8 37-5 37.0 37-3 29-5 4 6.45 22.8 23.2 23.0 8 37-5 35.5 36.5 21.8 5 6.45 20.6 20.7 20.6 ' 8 33.5 35.0 34.3 24.5 6 6.45 19.8 20.0 19.9 8 44.0 42.5 43.3 43.0 7 6.45 20.4 22.5 21.4 8 40.5 45.0 42.8 38.0 8 6.45 20.8 23.2 22.0 8 34.0 33-5 33.8 19.3 9 6.45 21.4 20.4 20.9 8 42.0 40.5 41.3 37-3 10 6.45 21.9 23-9 22.9 8 39.0 39.0 39.0 27.2 APPENDIX I I Values obtained from Daily Feed and Fecal Study for Beaver 9 Day Per cent Cellulose Units of Chromic Oxide Apparent Digestibility i n feed i n feces in feed i n feces 1 2 Average 1 2 Average 1 6.9 24.2 25.2 24.7 9.6 18.0 18.5 18.3 - 87.9 2 6.9 9.6 3 6.9 21.9 21.4 21.6 9.6 21.0 22.0 21.5 - 39.8 4 6.9 20.0 20.6 20.3 9.6 28.5 28.5 28.5 0.9 5 6.9 18.8 18.5 18.6 9.6 35.5 35.0 35.3 26.7 6 6.9 21.0 21.5 21.3 9.6 33.0 31.5 32.3 8.3 7 : 6.9 22.4 22.1 22.6 9-6 33-0 34.0 33.5 3.6 8 6.9 22.3 19.3 20.8 9.6 40.0 42.0 41.0 29.4 9 6.9 26.0 23.6 24-8 9-6 34.0 33.0 33.5 - 3.0 10 7.5 22.3 23-0 22.6 7 37.0 38.0 37.5 43-8 11 7.5 21.2 20.8 21.0 7 31.5 28.0 29-8 34.2 12 7.5 24.4 23.7 24.1 6.8 29.0 29-5 29.3 25.4 13 7-5 24-9 23.5 24.2 6.8 29.5 31.0 30.3 25.1 14 7.5 20.8 21.0 20.9 6.8 28.5 26.5 27.5 31.1 APPMDLX I I I Values obtained from Daily Feed and Fecal. Study for Rabbit 1 Per cent Cellulose Units Chromic Oxide Apparent Digestibility Day i n feed , in'feces . . . ; in feed i n feces 1 2 Average 1. 2 Average 1 6.9 21.9 22.2 22.1 9.6 32.5 33.5 33.0 6.8 2 6.9 21.6 21.8 21.7 9.6 38.5 37.0 37.8 20.1 3 6.9 22.1 23.0 22.6 9.6 36.5 36.5 36.5 13.9 4 6.9 18.3 18.2 18.3 9.6 20.5 21.5 21.0 - 21.2 5 6.9 22.5 22.5 22.5 9.6 42.5 43.5 43.0 27.2 6 6.9 21.9 21.5 21.7 9.6 34.5 31.5 33.0 8.5 7 6.9 15.6 14.8 15.2 9.6 27.0 - 27.0 31.7 8 6.9 10.4 - 10.4 9.6 25.5 - 25.5 43.5 9 7-5 19.9 19.6 19.8 7 46.5 46.5 46.5 60.3 10 7-5 24.5 24.5 24.5 7 37-5 38.5 38.0 39-8 11 7-5 27.4 26.6 27.0 6.8 33-0 34.0 33-5 26.9 12 7-5 25.6 26.1 25.9 6.8 38.5 35-5 37.0 36.5 13 7-5 29.8 28.8 29.3 6.8 35.0 36.0 35-5 25.2 14 7.5 23-0 23.2 23.1 6.8 26.5 29.0 27.8 24.7 APPENDIX IV Values obtained from Daily Feed and Fecal. Study for Rabbit 2 Day Per.cent Cellulose Units Chromic Oxide Apparent Digestibility i n feed . i n feces in feed in feces 1 2 Average 1 2 Average 1 6.9 21.2 22.1 21.6 9.6 22.0 23.0 22.5 - 33.6 2 6.9 24.6 23.3 24.0 9.6 33-0 33.0 33.0 - . 1.2 3 6.9 23.0 22.9 22.9 9.6 • 41.0 45.5 43.3 • 26.4 4 6.9 22.6 22.6 22.6 9.6 36.0 - 36.0 12.7 5 6.9 21.4 20.9 21.2 9.6 35.5 35.5 35.5 16.9 6 6.9 21.3 28.1 24.7 9.6 32.5 33.0 32.8 - '4.8 7 6.9 18.6 22.5 20.5 9.6 24.5 23.0 23.0 - 19.8 8 6.9 25.8 32.3 27.9 9.6 37.0 37.0 37.0 - 4-9 9 7.5 22.3 20.5 21.9 7 30.5 28.5 29.5 30.8 10 7-5 20.6 19.9 20.3 7 29.0 28.0 28.5 33.5 11 7.5 26.8 22.6 24.7 6.8 25-5 26.5 26.0 13.9 12 7.5 22.4 35-7 29.0 6.8 24.5 22.5 23.5 - 11.9 13 7.5 35.7 31.9 33.8 6.8 24.5 24.5 24-5 - 25.1 14 7-5 24.4 23.4 23-9 6.8 24.5 23-5 24.0 9-7 APPENDIX V Values obtained from Daily Feed and Fecal Study for Mink 1 Day Per cent Cellulose Units Chromic Oxide Apparent Digestibility i n feed , i n fee es i n feed in feces 1 2 Average 1 2 Average 1 6.6 19.5 14.7 17.1 12.5 26.5 26.5 26.5 - 22.2 2 6.6 13.8 13.7 13.7 12.5 20.0 20.0 20.0 - 29.7 3 6.6 12.7 12.3 12.5 12.5 20.0 19.5 20.0 - 18.4 4 . 6.6 17-2 13.8 15.5 12.5 22.0 22.0 22.0 - 13.4 5 6.6 13.4 13.6 13.5 12.5 23.0 23.0 23.0 - 11.2 6 6.6 14.5 12.0 13.3 12.5 23.0 22.5 23-0 - 9.5 7 6.6 13.8 13.9 13.9 12.5 20.0 22.0 21.0 - 25.4 8 6.6 18.1 17.8 18.0 12.5 23.0 23.5 23-3 - 46.3 9 6.6 19.9 15.3 17.6 12.5 26.0 24.5 25-3 - 31.8 - 79 -LITERATURE CITED Aldous, S.E., Beaver Food Utilization Studies., Jour. 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