The effects of added fructooligosaccharide (Raftilose®P95) and inulinase on faecal quality and digestibility in dogs

Animal Feed Science and Technology 108 (2003) 83–93

The effects of added fructooligosaccharide (Raftilose®P95) and inulinase on faecal quality and digestibility in dogs L.N. Twomey a,1 , J.R. Pluske a,∗ , J.B. Rowe b , M. Choct b , W. Brown b , D.W. Pethick a b

a School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch WA 6150, Australia School of Rural Science and Agriculture, The University of New England, Armidale NSW 2351, Australia

Received 8 February 2002; received in revised form 9 April 2003; accepted 9 April 2003

Abstract A 3×2 factorial experiment was designed to examine the effects of dietary fructooligosaccharides (FOS) level, and the presence or absence of an enzyme (inulinase), on aspects of faecal quality and apparent coefficients of nutrient digestibility in dogs. Three extruded dry diets based on wheat, pearl barley and wheat by-products were formulated to contain (dry matter basis) 1.75 g/kg (Diet A), 4.7 g/kg (Diet B) and 61.7 g/kg (Diet C) FOS. The FOS content of Diets B and C was achieved by adding 30 and 60 g/kg (DM) Raftilose® P95, a commercial FOS product. The addition of inulinase (500 ml (1.2 × 106 U) per tonne) was examined for each diet to counteract any potentially negative effects of added FOS on faecal quality and digestibility, and was sprayed onto the diet at feeding at a level of 500 ml per tonne of food. The experiment lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were: faecal score (one indicating hard faeces, five indicating diarrhoea), coefficients of total tract apparent digestibility (CATTD), faecal pH, and volatile fatty acids (VFA) and lactate concentrations. The CATTD for fat and energy decreased with greater levels of dietary FOS. Increased levels of FOS decreased (P < 0.05) faecal pH and the content of dry matter (DM) in the faeces and also increased (P < 0.05) the faecal score, although this remained in the ‘ideal’ range of 1.5–2.5. Addition of inulinase increased (P < 0.05) the faecal pH. Faecal lactate concentrations increased with greater levels of FOS (P < 0.05; 84.9 versus 142.5 versus 288.7 mmol/kg faeces DM for Diets A, B and C, respectively), suggesting that the growth and (or) activity of lactate-producing bacteria in the colon were enhanced. Higher levels of FOS in an extruded dog food caused faeces to become wetter and more acidic, and consequently the number of dogs that had unacceptable faecal scores increased. However, and at the highest dietary ∗ Corresponding author. Tel.: +61-8-9360-2012; fax: +61-8-9310-4144. E-mail address: [email protected] (J.R. Pluske). 1 Present address: VMTH—Clinical Pathology, College of Veterinary Medicine, University of Florida, P.O. Box 100103C, Gainesville, FL 32610-0103, USA.

0377-8401/03/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0377-8401(03)00162-7

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FOS level (61.7 g/kg DM), inulinase caused significantly drier faeces and increased the number of dogs within the ‘ideal’ range of faecal score. © 2003 Elsevier B.V. All rights reserved. Keywords: Fructooligosaccharides; Inulinase; Dogs; Faeces; Digestibility

1. Introduction The use of fructooligosaccharides (FOS) in animal nutrition has attracted considerable recent interest, primarily because they might act as a modulator of colonic bacterial populations and fermentation end-products potentially to improve host health (Czarnecki-Maulden, 2000; Flickinger and Fahey, 2002). FOS are not digested in the small intestine by endogenous enzymes, and enter the large intestine to be fermented by the microflora to produce volatile fatty acids (VFA), lactate and gases (Cummings and Englyst, 1995; Gibson et al., 1995; Salminen et al., 1998; Van Loo et al., 1999). These properties qualify FOS as a type of dietary fibre (Cummings and Englyst, 1995). FOS are water soluble, but do not increase viscosity of the intestinal contents (Niness, 1999; Schneeman, 1999). Viscosity of the digesta is usually associated with soluble non-starch polysaccharides (NSP), and results in reduced digestion (Roberfroid, 1993). Due to their non-viscous nature, FOS are not thought to significantly affect digestibility (Schneeman, 1999). FOS have been identified as prebiotics (Gibson and Roberfroid, 1995), which are food ingredients that are not digested by small intestinal enzymes but are fermented in the large intestine to stimulate selectively the growth of probiotic-like bacteria that are part of the commensal gut microflora (Salminen et al., 1998; Macfarlane and Cummings, 1999). Gibson and Roberfroid (1995) added to this definition by stipulating that the stimulation of these bacteria would improve health of the host. The bacteria responsible for this in humans are Bifidobacterium spp. and Lactobacillus spp. (Gibson and Roberfroid, 1995). It is likely that probiotic bacteria in the canine large intestine are stimulated similarly by dietary FOS (Strickling et al., 2000). The gut health benefits of prebiotics include the exertion of an antibacterial effect on potentially pathogenic bacteria through production of acids which causes a reduction in intestinal pH, reduction of ammonia levels through protonation of NH4 + , production of B group vitamins, and immunomodulation in the gut mucosa (Gibson and Roberfroid, 1995). It would appear, therefore, that the routine addition of FOS to dry dog foods might provide beneficial effects on intestinal health for dogs. However, dry dog foods generally contain high levels of cereals and cereal by-products that contain considerable quantities of non-starch polysaccharides (NSP), including soluble NSP, which are readily fermented and can have negative effects on digestibility and faecal quality in dogs (Fahey et al., 1990). There is a risk that increased inclusions of FOS in dog foods could add to the fermentative load in the large intestine of cereal-based dog diets, leading to faecal deterioration. The aims of the current study were to (1) investigate the effects of increasing levels of dietary FOS, achieved by adding the commercial FOS product Raftilose® P95 to a basal diet containing 10.4 g FOS/kg, on digestibility and faecal quality in dogs, and (2) examine the

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influence of the enzyme inulinase to reduce any negative effects that might be created by higher levels of dietary FOS. The use of an enzyme is based on the premise that negative effects of fermentable fibrous ingredients in other animals, such as the pig, can be reduced using supplementary feed enzymes (Pluske et al., 1999). 2. Materials and methods 2.1. Study animals and care Thirty-six mixed breed dogs, aged between 10 months and 6 years, were kept in individual cages at a kennel facility at The University of New England, Armidale, NSW, Australia. On arrival the dogs were weighed and de-wormed with Canex All-Wormer (Pfizer Animal Health, West Ryde, NSW, Australia). Each dog’s rectal temperature was taken as a simple determinant of good health (less than approximately 39 ◦ C indicates potential health problems). 2.2. Experimental design, diets and feeding The experiment was designed as a 3 × 2 factorial arrangement of treatments with the respective factors being three dietary quantities of FOS and the presence or absence of enzyme (inulinase). The dogs had been fed a commercial cereal-based diet containing barley, mill mix (wheat bran plus wheat pollard wheat) and wheat for 4 weeks prior to the experiment. The dogs were allocated at random on the basis of body weight to the six treatment groups. The experiment lasted for 13 days, with the diets being introduced gradually over the first 4 days. The experiment was run as two replicates, with three dogs per treatment group in each replicate. The University of New England Animal Ethics Committee approved all procedures conducted during this experiment. The experimental diets (Table 1) were based on an extruded dry dog food, with supplemental Raftilose® P95 (Mandurah Australia Pty Ltd., Matraville, NSW, Australia) replacing a portion of the wheat in two of the diets. Wheat, barley and wheat by-products contain between 1.4 and 5.1 mg/g (DM) FOS (Hussein et al., 1998), which Lewis (1993) defined as a mixture of 1-ketose (1-kestotriose), nystose (1,1-kestotriose) and 1F -β-fructofuranosylnystose (1,1,1-kestopentanose). Based on the ingredient composition in Table 1, the calculated basal level of FOS (DM basis) in the diets was 1.75 g/kg (Diet A), 1.71 g/kg (Diet B) and 1.67 g/kg (Diet C). The total dietary FOS content of Diets B (31.7 g/kg) and C (61.7 g/kg) was achieved by adding Raftilose® P95, a commercial FOS product with an average degree of polymerisation of 12, at a rate of 30 and 60 g/kg (DM) to each diet, respectively. Raftilose® P95 is a mixture of oligofructose (>930 g/kg), glucose, fructose and sucrose. The diets had the marker Celite (Celite Corporation, Lompoc, California, USA) included at a level of 20 g/kg, which was determined as acid-insoluble ash using the technique described by Choct and Annison (1992). An enzyme solution containing inulinase (500 ml, 1.2 × 106 U) (Novozymes Pty. Ltd., North Rocks, NSW, Australia) was prepared in sufficient quantity for each tonne of food manufactured, following a 400 times dilution to aid homogeneity of mixing. The enzyme solution was sprayed onto the feed at the time

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Table 1 Composition of the experimental diets (g/kg) Ingredient

Diet Aa

Diet B

Diet C

Raftilose® P95 Wheat Pearl barley Mill mix (wheat bran and pollard) Vitamin and mineral premixb Animal by-product mealc Beef tallow Celite Chemical composition (g/kg DM) Dry matter Total NSP Insoluble NSP Soluble NSP Total Starch Gross energy (MJ/kg) Protein Fat MEd (calculated) (MJ)

0 563 125 146 50 77 19 19

30 535 125 146 50 77 19 19

60 504 125 146 50 77 19 19

932 101.3 88.3 13.0 475.2 18.7 133.3 99.8 15.6

931 101.1 88.8 12.3 447.4 18.8 142.1 99.8 15.6

942 100.3 88.4 11.8 415.7 18.8 137.5 92.3 15.4

a

Diets A, B and C contained 1.7, 31.7 and 61.7 g/kg FOS (DM), respectively. Composition of vitamin and mineral mix withheld by manufacturer. c Poultry and mammalian origin, composition withheld by manufacturer. d Metabolisable energy (NRC, 1985). b

of feeding. The dogs that did not receive the enzyme had an equivalent amount of water added to their diets. The maintenance energy requirement for dogs was calculated as metabolisable energy (ME) (kJ) = 460 × BW0.75 (Harper, 1998). This amount was increased by 20% to ensure the dogs would maintain their body weight, and then used to calculate the amount of food needed daily using the calculated metabolisable energy concentration of the diets (National Research Council, 1985). The dogs were fed once a day in the evenings and fresh water was constantly available. 2.3. Analytical methods and coefficients of total tract apparent digestibility (CTTAD) Faecal samples were collected from each dog on each of the final 5 days of the experiment. The faecal samples were scored using the Waltham Faeces Scoring System (Waltham Centre for Pet Nutrition, Melton Mowbray, Leicestershire, UK). A score of one indicated hard, dry faeces and a score of five indicated runny diarrhoea. The faecal pH was measured immediately after collection (Activon Digital pH meter). Faeces were then dried at 80 ◦ C until constant weight was achieved, and equilibrated to room temperature and weighed (Mollah, 1985). The five samples for each dog were pooled and then ground using a 1 mm screen. The diets were dried at 105 ◦ C for 18 h to determine the dry matter content (DM). The total starch content of the diets and faecal samples was determined using the Megazyme Total Starch Assay Kit (Megazyme Australia Pty.,

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Warriewood, NSW, Australia), involving enzymatic hydrolysis with ␣-amylase and amyloglucosidase. The gross energy content of the diets and faecal samples was determined using a DDS isoperibol calorimeter (Digital Data Systems, Johannesburg, South Africa). The nitrogen content of the diets and faecal samples was determined using a Leco Nitrogen Analyser (FP-2000, Castle Hill, NSW, Australia). The protein content was calculated by multiplying N by 6.25. The fat content of the faecal samples was analysed by soxhlet extraction using Association of Official Analytical Chemists Official Method 991.36 (Venturetech Laboratory, Perth, WA, Australia) (AOAC, 1995). The fat content of the feed was analysed by acid hydrolysis followed by Soxhlet extraction using the AOAC Official Method 954.02 (Dairy Technical Services, Kensington, Victoria, Australia) (AOAC, 1995). Soluble and insoluble NSP and free sugars were determined by a combination of the methods of Englyst and Hudson (1993) and Theander and Westerlund (1993). Total lactic acid content of the faecal samples was determined on a Cobas Bio Automatic Analyser (Roche Diagnostics, Sydney, NSW, Australia) using a d- and l-lactic acid kit (Boerhinger Mannheim Australia, Castle Hill, NSW, Australia). The concentrations of volatile fatty acids in the faecal samples were determined using the internal standard method on a gas–liquid chromatograph (Hewlitt Packard Model 5890A, Packard Instruments, Sydney, NSW, Australia) (Kocher et al., 2000). The CTTAD were determined using the ratio of marker to nutrient in the feed and faeces. 2.4. Statistical analyses The ANOVA function of the statistical package StatView 5.0 for Windows (AddSoft Pty. Ltd., Woodend, Vic., Australia) was used to analyse the data in accordance with the 2 × 3 factorial arrangement of the study. An ANOVA measure of the mean values of the 5-day collection period was done for each group, followed by a Fisher’s protected least significant difference (PLSD) test. A χ2 -test with Yates’ correction for continuity was performed on the numbers of dogs in each treatment group within the ideal faecal score range (1.5–2.5), followed by post hoc cell contributions to determine the contributions made by each cell to the χ2 -statistic. 3. Results 3.1. Coefficient of total tract apparent digestibility (CTTAD) The CTTAD of starch was virtually complete (1.0) in dogs fed all diets, and was unaffected (P > 0.05) by both the amount of dietary FOS or addition of inulinase. The CTTAD of fat decreased (P < 0.05) with a greater amount of dietary FOS (0.90 versus 0.90 versus 0.89 for Diets A, B and C, respectively). The CTTAD of gross energy also decreased (P < 0.05) with more dietary FOS (0.79 versus 0.77 versus 0.77 for Diets A, B and C, respectively). A significant interaction existed between the amount of dietary FOS and inulinase for protein digestibility (P < 0.05), where addition of the enzyme significantly increased the CTTAD in Diet C. The addition of inulinase decreased (P < 0.05) the CTTAD of DM (0.92 versus

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Table 2 Coefficients of total tract apparent digestibility and digestible energy contents (DE MJ/kg DM) of the diets

Diet Aa Diet A + enzyme Diet B Diet B + enzyme Diet C Diet C + enzyme S.E.D.b P-value FOS level (F) Enzyme (E) F×E S.E.D.b

Starch

Fat

Protein

Gross energy

Dry matter

Digestible energy

1.00 1.00 1.00 1.00 1.00 1.00 0.001

0.91 0.90 0.90 0.90 0.89 0.89 0.007

0.75a ,b 0.72a ,c 0.71c 0.74a ,b,c 0.72c 0.75b 0.018

0.79 0.78 0.77 0.78 0.76 0.78 0.001

0.92 0.91 0.92 0.91 0.92 0.91 0.004

14.8 14.6 14.5 14.6 14.2 14.6 0.187

0.060 0.110 0.381 6.666 × 10−5

0.031 0.467 0.420 0.007

0.551 0.262 0.014 0.001

0.021 0.421 0.072 0.018

0.672 0.031 0.951 8.250 × 10−4

0.111 0.417 0.072 0.317

a

Diets A, B and C contained 1.7, 31.7 and 61.7 g/kg FOS (DM), respectively. Standard error of difference (S.E.D.) between means for F × E interaction. c Standard error of difference (S.E.D.) between means for main effects. b

0.91), and tended (P = 0.072) to increase the digestible energy content in Diets B and C (Table 2). 3.2. Faecal characteristics Faecal scores increased (P < 0.05) with greater levels of dietary FOS, and this was not alleviated by addition of the enzyme (P > 0.05). There was a significant effect of treatment on the number of dogs in each group above the Waltham Faeces Scoring System ‘ideal’ faecal score range of 1.5–2.5 (P < 0.01). Feeding Diet C caused more dogs to have faecal scores above the ideal range (five out of six dogs) than Diet A (zero out of six dogs, with and without the enzyme) and Diet B plus enzyme (one out of six dogs). There were significant main effects of the amount of dietary FOS and enzyme for faecal pH and DM content in the faeces. Faecal pH decreased (P < 0.01) with more dietary FOS (5.5 versus 5.5 versus 5.25 for Diets A, B and C, respectively) and increased (P < 0.01) with the addition of the enzyme (5.2 versus 5.6). The content of DM in the faeces decreased (P < 0.05) with greater amounts of FOS (327 g/kg versus 303 g/kg versus 296 g/kg for Diets A, B and C, respectively) and increased (P < 0.05) with addition of the enzyme (297 g/kg versus 320 g/kg) (Table 3). 3.3. Faecal acid concentrations The quantity of dietary FOS and enzyme did not influence (P > 0.05) the faecal VFA concentration, or the molar proportions of individual VFA (data not shown). There was a significant main effect of dietary FOS level on the faecal lactate concentration. As the amount of FOS in the diet increased, the lactate concentration also increased (P < 0.05; 84.9 versus 142.5 versus 288.7 mmol/kg faeces DM for Diets A, B and C, respectively).

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Table 3 Faecal characteristics of dogs fed different diets

Diet Ab Diet A + enzyme Diet B Diet B + enzyme Diet C Diet C + enzyme S.E.D.c P-value FOS level (F) Enzyme (E) F×E S.E.D.d

Faecal score

Faecal score >2.5a

2.2 2.3 2.6 2.5 2.8 2.4 0.17

0 0 1 2 5 1 –

0.038 0.163 0.108 0.068

Faecal pH 5.4 5.6 5.3 5.7 5.0 5.5 0.11 0.004 <0.001 0.160 0.152

Faecal DM content (g/kg) 328 326 292 314 272 319 14.2 0.010 0.010 0.065 6.810 × 10−7

Numbers of dogs in each treatment group (n = 6) above the ideal faecal score range (1.5–2.5). Diets A, B and C contained 1.7, 31.7 and 61.7 g/kg FOS (DM), respectively. c Standard error of difference (S.E.D.) between means for main effects. d Standard error of difference (S.E.D.) between means for F × E interaction. a

b

Table 4 Faecal acid concentrations (mmol/kg faeces DM) Diet

VFA

Lactate

Total acida

Diet Ab Diet A + enzyme Diet B Diet B + enzyme Diet C Diet C + enzyme S.E.D.c P-value FOS level (F) Enzyme (E) F×E S.E.D.d

466.2 580.0 554.0 583.0 501.0 471.6 69.67

123.8 46.1 176.1 109.0 357.9 219.4 91.18

590.1 622.0 728.7 696.5 858.8 688.6 97.45

0.263 0.355 0.356 72.01

0.011 0.083 0.837 38.54

0.063 0.321 0.339 103.25

Total acid concentration = VFA + lactate concentration. Diets A, B and C contained 1.7, 31.7 and 61.7 g/kg FOS (DM), respectively. c Standard error of difference (S.E.D.) between means for main effects. d Standard error of difference (S.E.D.) between means for F × E interaction. a

b

Trends were present for higher FOS levels to increase the total faecal acid concentration (P = 0.06) and for the addition of the enzyme to reduce the faecal lactate concentration (P = 0.08) (Table 4). 4. Discussion Oligosaccharide products are often included in dog food for their perceived benefits in improving gut health. However, inclusion of high levels of such products can lead to

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loose faeces, with increased fermentation (Niness, 1999; Schneeman, 1999), and perhaps reduced nutrient availability (Diez et al., 1997; Strickling et al., 2000). In the current study, increasing the amount of FOS in dog food caused the faeces to become wetter and more acidic, as high levels of acids were produced. Consequently, the number of dogs that had unacceptable faecal scores increased. Higher dietary levels of FOS, achieved by adding supplementary Raftilose® P95, caused faecal lactate concentration to increase with an associated decrease in faecal pH. The presence of FOS in the large intestine most likely stimulated the growth and (or) activity of the lactate-producing bacteria, Lactobacillus spp. and Bifidobacteria spp. The numbers of Lactobacillus spp. and Bifidobacteria spp. were not determined in this study, however some studies in dogs (Flickinger et al. unpublished data; cited in Flickinger and Fahey, 2002) showed changes in Bifidobacteria spp. populations with supplemental oligofructose (from sucrose). In another study reported from the same laboratory, Swanson et al. (cited in Flickinger and Fahey, 2002) reported increases in Lactobacillus populations and decreases in chemical indicators of faecal odour with added oligosaccharides. The mechanisms by which faecal pH and acid concentrations are manipulated by fermentation patterns are associated with the end products from the fermentation process. As fermentation occurs, lactate is rapidly converted to VFA in the large intestine (Rowe et al., 1997). Increased fermentation due to greater substrate availability causes accumulation of these acids, resulting in a decrease in intestinal pH and therefore also faecal pH (Rowe et al., 1997). Lactate-converting bacteria are sensitive to low pH and thus become inefficient, causing lactate to build up and the pH to decrease further (Rowe et al., 1997). During this process, the fermentation pattern changes such that lactate is favourably produced over VFA. This was seen in an in vitro experiment using human microflora (Holtug et al., 1992), where low pH inhibited fermentation to VFA. Shifts in fermentation patterns may also affect stool quality. Studies in sheep (Rowe et al., 1997) and humans (Vernia et al., 1988) suggest that VFA tend to be absorbed quickly from their site of production, and stimulate absorption of water from the intestine (Vernia et al., 1988). Lactate, however, is not absorbed readily and does not stimulate water absorption from the gut (Vernia et al., 1988). By remaining in the intestinal lumen, lactate tends to contribute to the osmotic pressure of the intestinal contents, causing wetter stools (Rowe et al., 1997). In addition, lower VFA concentrations cause less water to be absorbed from the intestine (Rowe et al., 1997). Therefore, higher FOS levels in the diet caused a shift in fermentation towards lactate production, leading to increased faecal water, decreased DM percentage in the faeces and higher faecal scores. The addition of inulinase, which degrades fructans with glucosyl ␣(1 → 2) (fructosyl)n ␤(2 → 1) fructose linkages, was effective in negating the ability of FOS to increase fermentation and reduce pH, suggesting that the effect of FOS was due to their highly polymeric nature. Addition of the enzyme increased faecal pH and tended to decrease the faecal lactate concentration (P = 0.08). The reduction in lactate production may be a reflection of the altered substrates available for fermentation. The enzyme cleaves the FOS molecule, resulting in smaller oligosaccharide molecules entering the large intestine. These oligosaccharide molecules may not selectively stimulate Lactobacilus spp. and (or) Bifidobacteria spp. to the same extent as the original FOS molecules, and may also be suitable substrates for many other bacterial species. This could lead to broader stimulation of bacteria in the

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large intestine. With less stimulation of Lactobacilus spp. and (or) Bifidobacteria spp. there may be lower lactate production, allowing the pH to remain higher. The lower intestinal concentration of lactate may have also contributed to the increased faecal percentage dry matter due to a reduced osmotic load in the intestine (Rowe et al., 1997). Faecal consistency is one of the most important parameters for the evaluation of dog foods. Excessive fermentation in the large intestine caused by the presence of a high level of FOS is of some concern to the pet food industry. Increased levels of FOS in the diet caused the mean faecal score to increase, indicating that the dogs fed Diet C had looser stools. More dietary FOS also caused the DM content of faeces to decrease. The action of FOS on stool consistency is probably twofold. First, the FOS molecules have a direct effect on faecal bulk due to a portion that will remain undigested in the intestinal tract to provide volume to the faeces via physical and osmotic effects (Schneeman, 1999). Second, FOS can provide stool softness through the increased bacterial mass that occurs with more fermentation in the large intestine (Schneeman, 1999). With increased fermentation, the bacteria in the gut multiply giving more bulk to the faeces, causing a laxative effect (Schneeman, 1999). Fermentation products can also act osmotically to increase faecal water content (Rowe et al., 1997). These two factors interplay to cause softer stools with higher levels of FOS in the diet. Although higher FOS levels had a significant negative effect on faecal quality, the level of FOS in Diet C (61.7 g/kg DM) is probably greater than would normally be used in a commercial dog food. Inclusion of oligosaccharides in dog food at a lower level of 5 g/kg DM did not negatively affect nutrient digestibility or faecal quality (Strickling et al., 2000). Therefore, at lower levels of inclusion, FOS may provide faecal softness without diarrhoea or reduced nutrient digestibility, and hence may be a useful source of DF in dog foods. Inulinase added to Diet C caused more dogs to have faecal scores within the ideal faecal score range of 1.5–2.5 (five out of the six dogs) than Diet C without inulinase (one out of the six dogs). Addition of the enzyme to Diet C also increased the DM content of the faeces and thus caused firmer, drier faeces. Increased faecal content of DM most likely occurred due to the partially degraded oligosaccharide molecules having less capacity to hold water than the larger, undegraded FOS molecules. There were a number of significant effects of both FOS level and enzyme, however the negative effect of higher FOS levels on the CTTAD for starch, fat and energy were generally small. The minimal negative effects of FOS on digestion in the small intestine is similar to those reported in previous studies (Diez et al., 1997; Schneeman, 1999; Strickling et al., 2000), and are most likely due to the inability of FOS to increase digesta viscosity dramatically in the small intestine (Schneeman, 1999). Without an increase in digesta viscosity, there is generally less interference with the processes of digestion and absorption (Schneeman, 1999). Addition of the enzyme improved the CTTAD of protein in Diet C, however no other coefficients were affected.

5. Conclusion The results from the current experiment suggest that a higher amount of FOS in dog diets caused increased fermentation in the large intestine while having minimal effects on digestion. More dietary FOS caused deterioration in faecal quality with softer and wetter stools.

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The addition of the enzyme, however, caused drier faeces and increased the proportion of dogs within the ideal faecal score range in Diet C, which contained 61.7 g/kg (DM) of FOS. The faecal lactate concentration increased with increasing dietary FOS levels, suggesting that shifts in fermentation occurred with changes in the intestinal environment, microflora and the substrates available for bacterial fermentation. The negative effects of FOS, and potentially other naturally occurring oligosaccharides, on digestibility and faecal quality may add to those of other fermentable dietary ingredients. Therefore, the cumulative detrimental effects of FOS and other cereal ingredients need to be considered during the formulation of cereal-based dog diets.

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