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ÿþBASIC NUTRITIONAL INVESTIGATION Influence of Fiber Fermentability on Nutrient Digestion in the Dog Jennifer Silvio, MS, David L. Harmon, PhD, Kathy L. Gross, PhD, and Kyle R. McLeod, PhD From the Department of Animal Sciences, University of Kentucky, Lexington, Kentucky; Hill s Pet Nutrition, Topeka, Kansas; and the USDA, ARS, Beltsville, Maryland, USA Eight mature dogs (17.2 0.2 kg) surgically fitted with ileal T-cannulas were used in a replicated 4- -4 Latin-square-design experiment to evaluate nutrient disappearance at the terminal ileum and through the digestive tract. Two fiber types, cellulose, a crystalline, slowly fermented fiber, and pectin, a soluble, rapidly fermented fiber, were fed in different increments, and the effects on nutrient availability were assessed. Treatments included 1) 100% cellulose, 2) 66% cellulose and 33% pectin, 3) 66% pectin and 33% cellulose, and 4) 100% pectin. Fiber was added at 10% of diet dry matter (DM). Diets were fed at 100% of ME for maintenance and offered at 0730 and 1730 h. All periods were 21 d, which included 3 d of diet transition and 7 d of adaptation. Daily DM intake was 210 5 g. Total tract and large-intestine DM digestibility increased linearly (P 0.01) with increased pectin. These changes in DM digestion were largely the result of changes in fiber digestion. Fermentation of total dietary fiber in the large intestine went from less than zero to 39% of ileal flow (linear, P 0.01). Total-tract crude-protein digestibility decreased linearly (P 0.01) with increased pectin. This study demonstrated that fiber fermentability significantly affects digestion in the dog. Increasing fermentable fiber increased the digestion of DM and energy. However, increased fiber fermentability inversely affects crude protein digestibility. The lower crude-protein digestibility could be attributed to larger microbial protein excretion as a result of greater fermentation of pectin versus cellulose. Nutrition 2000;16:289 295. ©Elsevier Science Inc. 2000 Key words: canine, fiber, fermentation, digestion, ileum Examples of these fiber types include the rapidly fermented pectin INTRODUCTION and the slowly fermented cellulose. The following experiment focused on both of these fiber types, alone and in combination, and The effects of fiber on nutrient availability and gastrointestinal on their effects on nutrient digestibilities and large-intestinal fer- health and function have received considerable attention in recent mentation characteristics in the dog. years. Much of the research has been performed using the human as a model; however, the less complex digestive tract of the dog makes direct comparisons difficult. The effect of different dietary MATERIALS AND METHODS fiber sources on nutrient digestibility, gastrointestinal motility, and stool characteristics in healthy dogs consuming adequately bal- Dogs anced diets has been evaluated.1 5 For optimum health, a good fiber source should be moderately fermentable for the production Eight mature, female mongrel dogs with body weights of 17.2 of short-chain fatty acids (SCFA) with a non-fermentable compo- 0.2 kg were used throughout this experiment to evaluate nutrient nent to provide bulk. The majority of previous research has fo- disappearance at the terminal ileum and through the digestive tract. Approximately 20 mo before this experiment, a polyvinyl chloride cused on the effects of only one fiber type.6 Therefore, the dietary T-cannula was surgically fitted 6  10 cm from the ileal-cecal fiber included did not necessarily contain both soluble and insol- uble components. An exception was seen in a previous study3 junction and exteriorized through the body wall.7 This allowed for the sampling of digesta and the determination of intestinal digest- where graded levels of beet pulp, a moderately fermentable source ibilities with minimal contribution of the post-small-intestinal containing both soluble and insoluble fiber, were fed to establish microflora. the level of inclusion in the diet necessary for adequate nutrient The animals were located in the Division of Laboratory Animal digestibility and acceptable stool characteristics. Resources at the University of Kentucky and were cared for in The ever-increasing roles of dogs as both pets and experimental accordance with IACUC protocols. All dogs were individually models are necessitating further research in the area of both rapidly housed in stainless-steel metabolism cages (1.2 1.8 m), with fermentable and slowly fermentable fiber inclusions in the diet. steps (1.01 0.46 m) covered by raised, holed mats. These cages were located in an environmentally controlled room at 22°C with a 14-h:10-h light:dark schedule. Within their cages, the dogs had unlimited access to nipple waterers and nylon chew toys. While their cages were cleaned, all dogs were exercised daily in two This study was approved by the Director of the Kentucky Agricultural groups for approximately 25 min. Experiment Station as Paper 99-07-33. Correspondence to: David L. Harmon, PhD, Department of Animal Sci- Feeding and Treatments ences, University of Kentucky, 809 W.P. Garrigus Building, Lexington, KY 40546 0215, USA. E-mail: dharmon@ca.uky.edu The diets included in this experiment were prepared by the Hills Date accepted: Dec. 6, 1999. Science and Technology Center (Topeka, KS, USA). Each diet Nutrition 16:289 295, 2000 0899-9007/00/$20.00 ©Elsevier Science Inc., 2000. Printed in the United States. All rights reserved. PII S0899-9007(99)00298-1 290 FIBER AND DIGESTION IN THE DOG TABLE I. fecal collection, all feces were removed from the cages and dis- carded before 0730 h. Fecal output from this point on for the next 3 d was collected at feeding and composited for each dog. During INGREDIENT COMPOSITION OF THE DIETS* fecal collection, the dogs were fitted with ruffed collars for in- creasing increments of time between the 0730-h and the 1730-h Treatments feedings to let them become adjusted to wearing the collars. The ileal sampling period consisted of the 3 d after the fecal 66% 66% collection. Dogs were fed at 0730 h and fitted with ruffed collars Cellulose Cellulose Pectin Pectin upon removal of their bowls. These collars restricted the dogs from removing the plastic collection bags attached to their ileal cannulas Ingredient during sampling hours while allowing them to drink from nipple Rice 56.0 56.0 56.0 56.0 waterers and water bowls located outside of their cages. Ileal Poultry byproduct meal 21.0 21.0 21.0 21.0 sampling began at either 0800 h or 0900 h and occurred every Pectin  3.33 6.67 10.00 other hour during the time period between the morning and Cellulose 10.00 6.67 3.33  evening meals, ending at 1700 h. The first 2 d included collecting Animal fat 8.5 8.5 8.5 8.5 during the even hours and collection during the odd hours occurred Natural flavor 2.0 2.0 2.0 2.0 on the third day to allow for samples to be composited for all hours Soybean oil 1.0 1.0 1.0 1.0 between 0730 h and 1730 h. One-ounce Whirl-Pak collection bags Potassium chloride 0.70 0.70 0.70 0.70 (Nasco, Fort Atkinson, WI, USA) were placed on the ileal cannu- Salt 0.28 0.28 0.28 0.28 las and then removed after 1 h. The bags were observed closely in Chromic oxide 0.20 0.20 0.20 0.20 case of leakage or the need for replacement when they became too Choline chloride 0.20 0.20 0.20 0.20 full. The content of the bags was weighed into tared collection Vitamin mix 0.06 0.06 0.06 0.06 containers and stored frozen for the remainder of the collection Mineral mix 0.04 0.04 0.04 0.04 period. Ethoxyquin 0.02 0.02 0.02 0.02 Nutrient composition Protein 21 22 21 22 Analyses Fat 14 14 15 14 Nitrogen-free extract 52 54 56 58 Ileal and fecal samples were both lyophilized. By weighing fecal Crude fiber 8.5 5.7 3.0 1.7 samples before and after lyophilization, DM was obtained. Ileal Neutral detergent fiber 9.5 8.7 5.6 5.6 and fecal samples were ground in a Waring 7010G laboratory Total dietary fiber 11.6 12.3 11.6 8.9 blender (New Hartford, CT, USA) and a Cyclotec 1093 Sample Calcium 0.8 0.7 0.8 0.8 Mill (Tecator, Hoganas, Sweden), respectively. Diet samples were Phosphorus 0.6 0.6 0.6 0.6 ground through a 1-mm screen in a Wiley mill. The dried and Chromium 0.15 0.14 0.14 0.15 ground samples were then stored in plastic bags at room temper- ature. DM for all ground samples were obtained by drying at 75°C * Ingredient and nutrient compositions on a dry-matter basis. under vacuum for 24 h. Ileal digesta was prepared for SCFA and ammonia analysis before lyophilization. Digesta was thawed and thoroughly mixed was formulated in accordance with the Association of American before 1 g was removed from each pooled sample (representing Feed Control Officials8 nutrient guide for dogs and balanced to individual dogs within each period) and centrifuged with 1 mL meet maintenance requirements (Table I). Any variabilities be- 25% metaphosphoric acid. The supernatant fluid was removed, tween diets were a result of the fiber inclusion, which was added placed in a vial, and frozen until analysis. For the determination of at 10% of diet dry matter (DM). Ten-percent dietary fiber was SCFA concentrations, samples were analyzed on a Hewlett Pack- chosen to maximize the effects of dietary fiber and maintain an ard 5890 Gas Chromatograph (Avondale, PA, USA) with a 1.8-m amount that would not be overly detrimental to energy intake or 4-mm glass column packed with 10% SP-1000/1%H3PO4 on stool quality. Two fiber types were combined in different incre- 100/120 Chromosorb W AW (Supelco, Bellefonte, PA, USA). The ments: 100% cellulose, 66% cellulose and 33% pectin, 66% pectin remaining contents of the vials were then analyzed for ammonia and 33% cellulose, and 100% pectin. All of the diets included the concentration with a Cobas Fara II (Roche Diagnostic Systems, addition of chromic oxide (0.20% of total diet DM), which served Branchburg, NJ, USA). The ammonia procedure9 was modified by as a marker for the determination of digestibility. Diets were replacing phenol with sodium salicylate. offered at 0730 and 1730 h and fed at 100% of ME for mainte- The ileal and fecal samples, along with those of the diet, were nance. All meals were preweighed into stainless-steel bowls. An wet ashed10 and stored in amber-colored glass bottles with screw- exception occurred during the third and fourth periods of the top lids at room temperature. The resulting liquid was analyzed for experiment, when one dog was fed at 125% of ME throughout chromium by atomic absorption spectroscopy (Unicam 929 Spec- because of weight loss. Dogs were allowed 15 min to consume the trometer, Thermo Jarell Ash, Franklin, MA, USA). Diet, ileal, and twice-daily meals, which was more than adequate for the complete fecal samples were analyzed for energy with a 1264 Isoperibol consumption of the diets. After the allotted time period, bowls Bomb Calorimeter (Parr Instrument Co., Moline, IL, USA). Crude were collected and any orts were recorded. The measured DM protein content of the samples were obtained by using a LECO intake of the dogs was 210 5 g/d. Throughout each of the four CNS2000 nitrogen analyzer (St. Joseph, MI, USA). periods, samples of the diets were pooled daily for analysis. Acid detergent fiber (ADF) was analyzed by using the proce- dure of Robertson and Van Soest.11 This procedure allowed for a measure of primarily the insoluble fiber components, cellulose, in Sampling the diet, ileal, and fecal samples. Total dietary fiber (TDF) was The study was performed in four consecutive 21-d periods. During determined as described previously.12 TDF is a measure of both the first 3 d of each period, dogs were fed a 1:1 blend of their the water-soluble and water-insoluble fiber components. Upon current diet and their next experimental diet to avoid any gastric completion of the procedure, the resulting residue contained both upset or meal refusal. A 7-d adaptation then followed, during the soluble pectin and insoluble cellulose consumed throughout which the dogs consumed their respective diets. On the first day of this experiment. The TDF procedure requires correction for ash FIBER AND DIGESTION IN THE DOG 291 TABLE II. INFLUENCE OF FIBER SOURCE ON DRY MATTER (DM) DIGESTIBILITY Treatments Contrasts* 66% 66% Item Celluose Cellulose Pectin Pectin SEM Linear Quadratic Cubic Body weight (kg) 17.2 17.3 17.2 17.2 0.2 0.64 0.74 0.54 DMI (g/d) 214.2 219.2 202.2 202.9 5.1 0.04 0.69 0.10 Fecal DM (%) 49.4 44.9 38.0 35.0 0.01 0.0001 0.57 0.30 Feces (g DM/d) 40.0 34.5 29.7 23.7 2.7 0.0003 0.93 0.87 Ileal flow (g DM/d) 45.5 39.4 42.5 42.7 4.2 0.78 0.46 0.53 DM digestibility Ileal (%) 78.9 81.7 79.1 79.1 2.0 0.84 0.49 0.38 Large intestine (%)! 10.4 12.1 28.4 43.3 2.2 0.0001 0.008 0.13 Total tract (%) 81.3 84.0 85.4 88.3 1.3 0.001 0.94 0.60 * Probability of a greater F value. Standard error of the mean, n 8. ! Percentage of ileal flow. DM, dry matter; DMI, dry matter intake. and protein content in the resulting residue. Whereas corrections to DM digestibility was unaffected by treatment. Muir et al.15 also ash content occurred, corrections for protein content did not occur reported decreased total-tract digestibility with the addition of because nitrogen analysis was unsuccessful. cellulose that did not affect ileal DM digestibility. Calculations and Statistics Starch Nutrient digestibilities were calculated as described previously13 Starch intake (Table III) decreased linearly (P 0.02) as pectin with chromium as a marker. The quantity of marker ingested was increased in the diet; however, the greatest difference was only 13 adjusted to the percentage recovered in the feces. g/d. These differences were related to the differences in DM The data were analyzed statistically as a replicated Latin-square intake. Ileal flow of starch increased (linear, P 0.0001) as pectin design by using the SAS Proc GLM.14 The experimental unit was increased in the diet. This increased ileal flow of starch was not dog. The statistical model consisted of square, periods within accompanied by an increased fecal loss of starch because fecal loss square, dogs within square, and treatments. Treatment responses was unaffected. This observation indicates that increasing the were separated by using linear, quadratic, and cubic contrasts. fermentable fiber, pectin, not only increases the fermentable fiber Treatment responses were considered different when P 0.05. presented to the large intestine but also increases starch fermented in the large intestine. These changes coincided with decreased ileal starch digestibility (linear, P 0.0001) and increased large- RESULTS AND DISCUSSION intestinal starch digestibility (linear, P 0.0001). Because of the increased digestibility in the large intestine, total-tract digestibility Dry Matter was unaffected by treatment and nearly complete, averaging 99.64%. It is unclear why pectin feeding decreased starch diges- There was a linear decrease (P 0.04) in DM intake (Table II) tion in the small intestine. Increasing pectin in the diet may have with increasing pectin. This difference was small, less than 12 g/d, decreased intestinal transit time, thereby decreasing time for di- and may have little biological significance. Muir et al.15 fed similar gestion, as was suggested previously.5 This may indicate that more combinations of pectin and cellulose and reported no changes in fermentable fibers such as pectin may be best suited for a reduced- DM intake; however, their fiber was limited to 7.5% of the diet. calorie diet. However, the advantages gained from decreased in- No differences (P 0.78) were seen in ileal flow (g DM/d), but testinal digestion may be more than offset by the increased large- fecal DM and fecal output (g DM/d) were highest for the cellulose intestinal fermentation. These differences may also contribute diets, decreasing linearly (P 0.0001 and P 0.0003, respec- greatly to the poor stool quality obtained. Pectin may also affect tively) as pectin content increased (Table II). This result can be digesta viscosity, resulting in altered enzyme access to substrate related to the water-holding capacity16 observed for both fiber and slightly lower starch digestion in the small intestine. types (with pectin exhibiting the greatest water-holding capacity) and also to the fibers respective fermentabilities.17 Dogs consum- ing the high-pectin diet had a more frequent, looser stool than did Crude Protein the dogs on the cellulose diet, which may indicate that additions of pectin to dog food may not be acceptable by pet owners because of There was a minor decrease in crude-protein intake (P 0.05), its effect on stool quality. Because cellulose is only partly digested largely the result of the differences in DM intake (Table IV). Ileal in the dog,2,18 it adds to fecal weight, whereas pectin, the rapidly flow of crude protein was unaffected by treatment, whereas fecal fermented fiber, contributes less to fecal output. The DM digest- loss of crude protein (g/d) increased linearly (P 0.009) with ibilities reported in Table II supported enhanced fermentability as pectin in the diet. No change was seen in ileal protein digestibility pectin increased. As pectin increased in the diet, digestibilities (P 0.60); however, large-intestinal crude protein digestibility were higher in both the large intestine (linear, P 0.0001; qua- decreased curvilinearly (linear, P 0.0001; quadratic, P 0.003) dratic, P 0.008) and total tract (linear, P 0.001), whereas ileal with increasing inclusion of pectin in the diet. Total-tract digest- 292 FIBER AND DIGESTION IN THE DOG TABLE III. INFLUENCE OF FIBER SOURCE ON STARCH DIGESTIBILITY IN DOGS Treatments Contrasts 66% 66% Item Celluose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Intake (g/d) 112.2 118.1 106.4 105.3 2.7 0.02 0.22 0.03 Ileal flow (g/d) 1.57 1.41 3.08 4.00 0.39 0.0001 0.18 0.15 Fecal loss (g/d) 0.42 0.34 0.38 0.46 0.07 0.64 0.31 0.80 Starch digestibility Ileal (%) 98.60 98.78 97.12 96.24 0.35 0.0001 0.14 0.11 Large intestine (%)! 72.16 76.49 86.42 89.38 1.96 0.0001 0.73 0.17 Total tract (%) 99.63 99.71 99.65 99.58 0.06 0.51 0.27 0.61 * Standard error of the mean, n 8. Probability of a greater F value. ! Percentage of ileal flow. ibilities of crude protein also decreased linearly (P 0.003) with Energy added pectin. These differences demonstrate the profound influ- Energy intake decreased slightly (linear, P 0.08) as pectin ence that fiber fermentability can have on estimates of total-tract increased (Table V). Ileal energy flow (P 0.42) was unaffected digestibility. Total-tract apparent-digestibility calculations do not by treatment. However, fecal energy flow decreased linearly (P take into account the nitrogen sink that occurs when fiber is 0.003) as pectin increased. Ileal energy digestibility was unaf- fermented in the large intestine. It is believed that the higher fected by treatment (P 0.70), whereas large-intestinal energy fermentative properties of pectin increases the microbial popula- digestibility increased curvilinearly (linear, P 0.0001; quadratic, tion, whereas cellulose, because of the reduced fermentability, has P 0.006) as pectin increased. These changes in large-intestinal little impact on fecal N-excretion. This was confirmed in a previ- digestion corresponded to a linear increase (P 0.007) in total- ous study15 where N-digestibility was similar for cellulose and tract energy digestibility. Fiber exerts its effects on nutrient digest- control diets. Other studies have reported increased fecal nitrogen ibilities and stool characteristics in the hind gut, where fermenta- excretion when fermentable fibers are fed.6,15,17 Using rats, tion occurs. The increase in digestibility seen in the pectin diets Younes et al.19 demonstrated that increased fiber fermentation in relates to its higher fermentative capacities when compared with the cecum coincides with an increased flux of blood urea nitrogen that of cellulose.17 to the cecum and an increased fecal nitrogen excretion. These results were later20 confirmed with nephrectomized rats. Feeding fermentable fiber to nephrectomized rats increased fecal nitrogen Acid Detergent Fiber excretion, decreased urinary nitrogen excretion, and lowered plasma urea by 30%. Similar responses have also been described The ADF is primarily a measurement of the insoluble component in humans.21 Wheat and oat bran were added to the diet of adult of fiber, consisting of cellulose in this study. This serves as an males, and both fiber sources increased fecal excretion; however, explanation for effects presented in Table VI. It was expected that oat bran, which contains more soluble fiber, increased fecal nitro- ADF intake would increase (linear, P 0.0001) with greater gen excretion more than wheat bran. amounts of dietary cellulose. Ileal ADF flow also increased (P TABLE IV. INFLUENCE OF FIBER SOURCE ON CRUDE PROTEIN DIGESTIBILITY IN DOGS Treatments Contrasts 66% 66% Item Cellulose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Intake (g/d) 44.9 45.6 42.3 42.6 1.1 0.05 0.86 0.13 Ileal flow (g/d) 14.2 11.5 12.9 14.0 1.3 0.92 0.17 0.48 Fecal loss (g/d) 7.7 8.7 10.5 11.3 1.0 0.009 0.87 0.66 Protein digestibility Ileal (%) 68.5 74.2 69.8 67.5 3.0 0.60 0.21 0.38 Large intestine (%)! 43.6 24.4 17.0 18.9 3.1 0.0001 0.003 0.86 Total tract (%) 83.0 80.7 75.3 73.6 2.2 0.003 0.89 0.51 * Standard error of the mean, n 8. Probability of a greater F value. ! Percentage of ileal flow. FIBER AND DIGESTION IN THE DOG 293 TABLE V. INFLUENCE OF FIBER SOURCE ON ENERGY DIGESTIBILITY IN DOGS Treatments Contrasts 66% 66% Item Cellulose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Intake (kcal/d) 1021 1055 974 980 24.5 0.08 0.58 0.08 Ileal flow (kcal/d) 189 157 168 166 15.6 0.42 0.34 0.42 Fecal loss (kcal/d) 161 141 126 106 11.5 0.003 1.0 0.83 Energy digestibility Ileal (%) 81.6 84.9 82.8 83.1 1.6 0.70 0.35 0.27 Large intestine (%)! 13.0 9.9 23.7 36.0 2.5 0.0001 0.006 0.11 Total tract (%) 84.3 86.5 87.1 89.2 1.1 0.007 0.95 0.56 * Standard error of the mean, n 8. Probability of a greater F value. ! Percentage of ileal flow. 0.0001) with increasing ADF intake. Fecal ADF loss decreased the diet, but this statistical decrease occurred largely because of a curvilinearly (linear, P 0.0001; quadratic, P 0.0009; cubic, lower value for the 66% pectin treatment. This difference was the P 0.0007, respectively) with added pectin. Ileal, large-intestinal, result of a lower TDF content for this diet and lower DM intakes. and total-tract ADF digestibilities all increased (P 0.01) curvi- No effect (P 0.21) was observed for ileal TDF flow (g/d); linearly with increasing pectin. There was an increase in small- however, fecal TDF loss decreased (linear, P 0.0001) with intestinal, large-intestinal, and total-tract digestibilities with addi- added pectin. This could be attributed to the higher fermentability tions of pectin to the diet. This may be caused by higher microbial of pectin. Fecal TDF loss decreased with higher pectin in the diet activity resulting from greater fermentability of pectin. However, because of pectin s greater disappearance in the large intestine. We ADF does a poor job of measuring the soluble fiber of pectin, as saw no differences (P 0.82) in ileal TDF digestibility; however, indicated by the decreasing intake of ADF as pectin increased in both large-intestinal and total-tract TDF digestibilities decreased the diet. Because of the decreasing ADF intake, the actual quan- linearly (P 0.0001) with increasing pectin additions to the diet. tities of ADF disappearing in the small intestine (g/d) were similar for all diets (range 2.6  4.0 g/d). This was in sharp contrast to Ammonia and SCFA the amounts of ADF digested in the large intestine, which was 9 g/d for the cellulose diet versus only 1 g/d for the pectin diet. Analysis of collected ileal samples showed that ammonia concen- trations (Table VIII) were highest for the cellulose diet and de- creased linearly (P 0.002) with increasing pectin. Because these Total Dietary Fiber are only concentrations in ileal digesta, they have limited interpre- The TDF procedure measures both the insoluble and soluble tation with regard to protein degradation and ammonia use. The components in dietary fiber. Therefore, the values observed in increased concentrations of ammonia may be indicative of more Table VII do a better job of accounting for both pectin and protein being fermented in the cellulose diets because the cellulose cellulose. A decrease (linear, P 0.0003; quadratic, P 0.0001; is less fermentable or of an enhanced rate of ammonia use in the cubic, P 0.002) in TDF intake occurred with increased pectin in pectin diets because of the greater fermentability. Ileal protein TABLE VI. INFLUENCE OF FIBER SOURCE ON ACID DETERGENT FIBER (ADF) DIGESTIBILITY IN DOGS Treatments Contrasts 66% 66% Item Cellulose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Intake (g/d) 24.9 19.8 10.8 3.9 0.5 0.0001 0.10 0.03 Ileal flow (g/d) 21.7 16.6 6.5 1.2 0.4 0.0001 0.78 0.0001 Fecal loss (g/d) 12.7 8.2 2.2 0.21 0.3 0.0001 0.0009 0.0007 ADF digestibility Ileal (%) 12.4 14.6 38.6 66.0 2.57 0.0001 0.0001 0.13 Large intestine (%)! 41.6 50.4 65.9 84.5 0.73 0.0001 0.0001 0.27 Total tract (%) 48.8 57.8 78.8 94.1 1.18 0.0001 0.01 0.004 * Standard error of the mean, n 8. Probability of a greater F value. ! Percentage of ileal flow. 294 FIBER AND DIGESTION IN THE DOG TABLE VII. INFLUENCE OF FIBER SOURCE ON TOTAL DIETARY FIBER (TDF) DIGESTIBILITY IN DOGS Treatments Contrasts 66% 66% Item Cellulose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Intake (g/d) 53.2 49.3 41.1 48.2 1.2 0.0003 0.0001 0.002 Ileal flow (g/d) 30.2 27.6 26.7 25.4 2.7 0.21 0.80 0.86 Fecal loss (g/d) 33.2 27.2 20.9 14.9 2.0 0.0001 0.99 0.95 TDF digestibility Ileal (%) 43.3 43.0 35.6 47.8 6.0 0.82 0.31 0.33 Large intestine (%)! 10.4 0.41 18.8 38.7 3.4 0.0001 0.19 0.69 Total tract (%) 37.7 44.1 49.4 69.0 4.1 0.0001 0.12 0.42 * Standard error of the mean, n 8. Probability of a greater F value. ! Percentage of ileal flow. digestibility was unaffected by fiber type (Table IV); thus, if fiber decreased (linear, P 0.0002) as pectin increased in the diet. The type affected protein fermentation, the effect must have been proportions of isobutyrate and isovalerate in the ileal samples small. decreased (linear and quadratic, P 0.02) as pectin increased. The results for total ileal SCFA concentration (Table VIII) These values coincide with the higher ammonia concentrations for show that higher concentrations are present in the cellulose diets the cellulose diets, indicative of greater protein fermentation as (linear, P 0.0001; quadratic, P 0.002). This would indicate cellulose increased. Butyrate and valerate proportions were unaf- that more fermentation of the cellulose-containing diets was oc- fected by treatment. curring at the terminal ileum. However, concentrations could be misleading because these are expressed as per gram of ileal di- gesta. Differences in ileal DM content and perhaps fiber water- CONCLUSION holding capacity could influence these results, but these values are unavailable. Pectin diets have a greater water-holding capacity16 Large-intestinal fermentation has a significant impact on total and should have had a lower ileal DM content. The differences in digestibility in the dog. Altering fiber type and subsequent fer- ileal SCFA concentrations could also have been the result of mentability follows the trend that the more fermentable the fiber, greater fermentation of the cellulose, perhaps a result of pectin the higher the digestibilty. This can be observed in most nutrient decreasing substrate degradation in the small intestine, as was seen digestibilities described in this study. An exception occurred in for starch. apparent nitrogen digestibility where there was an inverse effect. The proportions of SCFA produced indicate differences in the The increased excretion of colonic microbes when feeding a more substrates being fermented. Ileal acetate proportion increased (lin- fermentable fiber results in lower nitrogen digestibility. The ear, P 0.004; quadratic, P 0.02) and propionate proportion present results imply that combinations of pectin and cellulose, TABLE VIII. INFLUENCE OF FIBER SOURCE ON ILEAL AMMONIA AND SHORT CHAIN FATTY ACID (SCFA) CONCENTRATIONS Treatments Contrasts 66% 66% Item Cellulose Cellulose Pectin Pectin SEM* Linear Quadratic Cubic Ileal ammonia ( mol/g)! 34.0 32.3 26.6 29.0 1.3 0.002 0.12 0.05 Ileal SCFA (mol/100 mol) Acetate 72.8 77.7 80.2 78.5 1.3 0.004 0.02 0.75 Propionate 15.6 13.3 12.5 11.8 0.6 0.0002 0.20 0.61 Isobutyrate 2.0 .05 ND ND 0.1 0.0001 0.0001 0.57 Butyrate 7.2 6.9 14.9 9.1 3.8 0.43 0.49 0.21 Isovalerate 2.2 1.6 0.2 ND 0.1 0.0001 0.02 0.0002 Valerate 0.2 ND ND 0.6 0.2 0.25 0.10 0.70 Total ( mol/g)! 109.0 74.2 60.4 64.5 5.4 0.0001 0.002 0.90 * Standard error of the mean, n 8. Probability of a greater F value. ! Concentrations are per gram ileal digesta. ND, Non-detectable concentration. FIBER AND DIGESTION IN THE DOG 295 10. Kimura FT, Miller VL. Improved determination of chromic oxide in cow feed considered fermentable and non-fermentable, respectively, can be and feces. 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