cus distention, exfoliation and/or cryptitis), whereas dogs fed the pectin/gum arabic had the highest. Three of the five dogs fed beet pulp and one of the dogs fed.
Dietary Fiber
Source of Dietary Fiber and Its Effects on Colonie Microstructure, Function and Histopathology of Beagle Dogs1 GREGORY A. REINHART,* RODNEY A. AfOXLEYt AND EDGAR T. CLEMENS^2 *The IAMS Company, Lewisburg, OH 45338, and ^University of Nebraska-Lincoln, Department of Animal and Veterinary Sciences, Lincoln, HE 68583 EXPANDED
ABSTRACT
Indexing Key Words: •dietary fiber
TABLEl
•colonie Nutrient
analysis of dry extruded canine diets containing diffère n t sources of dietary fiber* Cellulose
The epithelium of the mammalian gastrointestinal tract is a metabolically active and rapidly renewing tissue. Colonocytes depend heavily upon a constant supply of respiratory fuels to maintain cellular func tion and turnover. The preferred energy source of colonocytes are short-chain fatty acids (SCFA) such as acetate, propionate and butyrate. SCFA are produced through fermentation of dietary fibers by anaerobic bacteria residing in the large intestine. Recent canine research has demonstrated variable rates of fiber fermentation and SCFA production that are highly dependent upon fiber source (Fleming et al. 1992, Sunvold et al. 1993). The presence of lumenal SCFA are associated with mucosal hypertrophy, in creased sodium and water absorption (Roediger and Moore 1981, Kripke et al. 1987), increased colonie blood flow (Kvietys and Gronger 1981) and increased colonie cell proliferation (Sakata and Englehardt 1983, Fleming et al. 1992). In the present study, diets that differed in fiber fermentability and SCFA generation were examined for effects on canine colonie microstructure and function. Procedures. Fifteen adult beagle dogs, 8.2-17.1 kg body weight, were used to assess the effects of dietary fiber upon colonie structure, function and histopathology. The three sources of dietary fiber used in the study were cellulose, beet pulp and pectin/gum arabic with diets being fed to the dogs for a minimum of 2 wks before laboratory examination. The selection of dietary fiber source was based on their fermentation capacity. Cellulose has been shown to be low in fer0022-3166/94
$3.00 ©1994 American Institute of Nutrition.
Beet pulp
Pectin/arabic
Crude proteinNitrogen extractFatTotal free
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•dogs •colon micro structure
fiberAshMoisture29.030.321.49.55.59.029.028.621.88.46.29.228.330.221.38.25.410.5 dietary
Certificate of analysis, The IAMS Company, Lewisburg OH.
mentation capacity, beet pulp moderately fermentable and pectin/gum arabic mixture highly fermentable (Sunvold et al. 1993). Diets were formulated to contain 6% supplemental fiber from the various fiber sources (Table 1). The remaining total diet fiber found in the diets were indigenous to the ingredients used in the formulations. All other nutrients were held constant and fed according to National Academy of Science re quirements for dogs (NAS 1974). On the day of the experiment each dog was weighed, anesthetized with intravenous sodium pentobarbital and placed in lateral recumbency. Dogs were main1Presented as part of the Waltham Symposium on the Nutrition of Companion Animals in association with the 15th International Congress of Nutrition, at Adelaide, SA, Australia, on September 23-25, 1993. Guest editors for this symposium were Kay Earle, John Mercer and D'Ann Finley. 2 To whom correspondence should be addressed: 224 Animal Science Building, University of Nebraska-Lincoln, Lincoln, NE 68583.
J. Nutr. 124: 2701S-2703S,
2701S
1994.
SUPPLEMENT
2702S TABLE 2
Colonie weight and mucosa! characteristics of dogs fed cellulose, beet pulp and pectin/gum arabic as their primary fiber source* Cellulose
Beet pulp
Colon g/kg weight, 0.130.146' 6.52" weightMucosal body surface-to-volume ratio,um/um2Mucosalenergetics,6.09' 0.1 56b
0.223 Mucosal DNA,
47.4'
0.206 40.0"
Pectin/ arabic
SE/LSM*
6.62" 0.1 54b
0.004
0.239
0.022
38.4b
3.09
1Values within a row with unlike superscripts are statistically different (P < 0.05). There were five dogs for each fiber source. * Standard Error of the Least Square Mean.
arabic, respectively). Although significant differences were not detected for the colonie transport of sodium, chloride, water
£ 0.9 |
0.8
x
I0'7 O
§ 0.6 ¡0, 0.4
Cellulose
Beet Pulp
Pectin/Gum Arabic
Source of Dietary Fiber
FIGURE 1 Net colonie absorption of acetate, propionate and butyrate as influenced by the source of dietary fiber fed beagle dogs. There were five dogs for each fiber source. Sta tistical differences were not detected among treatment groups (P > 0.05). SE/LSM for acetate (0.031), propionate (0.026) and butyrate (0.028).
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tained on methoxyflurane gas at a stage III, phase ii level of surgical anesthesia throughout the sample col lection period (Meyer et al. 1984). A midline incision was made in the abdominal cavity, the cecum located and a ligature placed at the ileocolonic junction to oc clude contamination of the colon with small intestinal contents. A perfusion catheter was inserted into the proximal colon, secured in place and a large bore col lection tube placed in the dog's rectum. The dog's co lon was rinsed for a minimum of 30 min with physi ological saline and then perfused with a warm test so lution (in mmol/1: sodium 110.9, chloride 16.1, acetate 31.3, propionate 29.5 andbutyrate 28.6) (Herschel et al. 1981). The test solution was perfused (3 ml/min) into the bowel via the ileocolonic perfusion catheter and the effluent collected every 10 min for the 120-min test period. On completion of the perfusion study, the cecum and entire colon were removed and tissues collected on ice. Analytical determinations were made for coIonic weight, mucosal surface-to-volume ratio, crypt depths and width, mucosal oxygen consumption and mucosal and serosal DNA content. The dogs were killed with intravenous sodium pentobarbital. The design of the experiment was a complete ran dom allocation of treatments, with dogs as the exper imental unit. Statistical differences were determined by SAS, with further analysis according to Tukey's grouping (SAS 1989). The desired level for assessing significant differences was set at P < 0.05. Results and discussion. Dogs fed cellulose as the principle dietary fiber source developed a lighter weight colon (per kg body weight of the animal) than dogs fed beet pulp or pectin/gum arabic (Table 2). Fur thermore, the colon of dogs fed the cellulose had a smaller mucosal surface area-to-volume ratio, relative
to those fed beet pulp or pectin/gum arabic. However, neither the depth nor width of colonie crypts were affected by dietary fiber source. Histopathological examination revealed that dogs fed beet pulp as the principle fiber source had the low est incidence of colonie mucosal disturbance (i.e., mu cus distention, exfoliation and/or cryptitis), whereas dogs fed the pectin/gum arabic had the highest. Three of the five dogs fed beet pulp and one of the dogs fed cellulose showed no signs of colonie histopathological disturbance. However, all five of the dogs fed the pec tin/gum arabic exhibited either mucus distension, ex foliation and/or cryptitis. Dogs fed the cellulose diet had the highest incidence of cryptitis (3 of 5). Statis tical analysis was not conducted on the histopatho logical data. Alterations in colonie microstructure is of impor tance, and influential, in the ability of the gut to trans port nutrients (Herschel et al. 1981). Although the ox ygen consumption of colonie mucosa was not signif icantly different among the three diets fed, treatment differences in mucosal DNA content were observed (Table 2). Dogs fed the cellulose diet had significantly higher DNA content per gram of tissue than did those fed beet pulp or pectin/gum arabic. One might suggest then that the higher DNA content of tissue derived from feeding cellulose resulted from, and/or compen sated for, the significant reduction in colonie mucosal surface area-to-volume ratio. The relationship between mucosal energetic activity and tissue DNA content may be further expressed as energetic activity per unit DNA. When doing so, mucosal tissues from dogs fed the pectin/gum arabic diet had the highest value (i.e., 0.470 X IO'2, 0.515 X IO-2 and 0.622 X 10~2 O2-¿tg DNA"1 -min'1 for cellulose, beet pulp &.pectin/gum
CANINE COLONIC MICROSTRUCTURE AND FUNCTION
or total SCFA, some basic observations were apparent. In the bowel of dogs fed cellulose, which was the least fermentable of the three fiber sources, the SCFAs (ac etate, propionate and butyrate) were transported in relatively equal proportions (Fig. 1). However, for the moderately fermentable beet pulp and highly fer mentable pectin/gum arabic diets, acetate and buty rate, respectively, were transported in higher propor tions than the other two fatty acids. Butyrate concen trations are known to rise with the increased fermentability of the fiber source (Kripke et al. 1987) and have also been implicated in the colonie cell pro liferation (Sakata and Englehardt 1983, Fleming et al. 1992). The preferred butyrate transport and greater histopathological incidence observed in dogs fed pec tin/gum arabic seems to fit these suggestions. The higher acetate transport, and low incidence in histo pathological examination, in dogs fed beet pulp is of interest and deserving of further investigation. CITED
Fleming, S. E., Fitch, M. D. & De Vries, S. (1992| The influence of dietary fiber on proliferation of intestinal mucosal cells in min
iature swine may not be mediated primarily by fermentation. J. Nutr. 122: 906-916. Herschel, D. A., Argenzio, R. A., Southworth, M. & Stevens, C. E. 119811 Absorption of volatile fatty acid, Na and water by the colon of the dog. Am. J. Vet. Res. 42: 1118-1124. Kripke, S. A., Fox, A. D., Berman, J. M., Settle, R. G. & Rombeau, J. L. (1987) Stimulation of mucosal growth with intracolonic bu tyrate infusion. Surg. Forum 38: 47-49. Kvietys, P. R. & Gronger, D. N. 11981 ) Effects of volatile fatty acids on blood flow and oxygen uptake by the dog colon. Am. J. Physiol. 80: 962. Meyer, F. H., Jewetz, E. &. Goldfiend A. (1984) Review of Medical Pharmacology. 8th eds, Chapter 20, General Anesthetics, p. 203. Lange Medical Pubi., Los Altos, CA. National Academy of Science (1974) Nutrient Requirements of Dogs. Vol. 8. Nutrient Requirements of Domestic Animals. Na tional Academy of Sciences, Washington, DC. Roediger, W. E. W. &. Moore, A. (1981) Effect of short-chain fatty acids on sodium absorption in isolated human colon perfused through the vascular bed. Dig. Dis. Sci. 26: 100. Sakata, T. &. Englehardt, W. V. (1983) Stimulating effect of shortchain fatty acids on epithelial cell proliferation in rat large in testine. Comp. Biochem. Physiol. A Comp. Physiol. 74: 459. SAS Institute Inc. (1989) SAS User's Guide. Statistics (Release 6.04 Ed.) SAS Institute, Cary, NC. Sunvold, G. D., Bourguin, L. D., Titgemeyer, E. C., Fahey, G. C. & Reinhart, G. A. (1993) Fermentability of various fibrous substrate by canine fecal microflora. FASEB J. 7: A740.
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LITERATURE
2703S
