Faeces volume and consistency are indicators of the quality of dog foods. Three independent feeding trials with dogs show that a fibrillated, cellulose-rich fibre lowers faeces volume, enhances digestion and maintains optimum faeces consistency.
In dog food marketing health claims are commonly used. These claims often are not easily understood, whereas the evidence may be loose or unverifiable. Claims that can be checked by dog owners are probably more effective for determining purchasing behaviour. Faeces volume and consistency are indicators of intestinal health and can be qualified by owners. This communication deals with the impact of dietary fibre type, at constant level of dietary crude fibre, on faeces characteristics and digestibility of macronutrients in dogs.
Pet food and faeces
Owners often inspect the consistency of faeces produced by their dog. Faeces consistency is considered an indicator of food quality in terms of digestibility. Optimum faeces consistency refers to well formed stools that are not too moist and loose, and not too dry and hard. Such faeces point at adequate food digestibility and good intestinal health. Optimum faeces consistency is highly appreciated by dog owners. Many owners also prefer low faeces volume and an associated low defecation frequency. Faeces assessment is critical during the process of developing pet foods. Optimum faeces consistency contributes to the sales success of the food on the market. In feeding trials, faeces quality can be scored consistently and objectively with the use of a grading scale. Faeces can be collected quantitatively and weighed to obtain an index of volume. The degree of digestion of macronutrients in the food can be determined as amount of intake minus faecal excretion and can be expressed as percentage of intake, representing the so-called apparent digestibility.
Type and amount of fibre
Fibre can be defined as the portion of the plant cell wall that is resistant to the dog's digestive enzymes. Industrially produced dog foods contain different types and amounts of fibre. The fibre component is present in core plant ingredients or is added as a fibre-rich feedstuff on preparation. Dietary fibres can have different physical and physiological properties. In contrast to insoluble fibres, the soluble fibres form viscous solutions and may be largely degraded by the colonic microflora. Thus, insoluble versus soluble fibres are more recovered in faeces.
Health claims on regular dog foods or indications for therapeutic foods may highlight the presence of soluble or insoluble fibre. Regarding fibre, commercially prepared canine foods are typified by their crude fibre content, which is compulsorily listed in the guaranteed analysis panel on the packaging. Crude fibre content is determined by boiling an ether-extracted food sample in dilute acid and then in dilute alkali. The combustible, organic residue is the crude fibre fraction. Analysed crude fibre in foods contains variable fractions of cellulose, lignin and hemicelluloses. Clearly, crude fibre analysis yields a nonspecific outcome with little physiological relevance. It is common practice to assume that crude fibre does not provide energy to dogs. Regular, dry dog foods contain 2-4% crude fibre. Light foods may contain up to 8% and veterinary weight reduction diets have higher levels. When expressed on a dry matter basis, wet dog foods contain similar concentrations of crude fibre.
The Arbocel preparations of cellulose and lignocellulose (J. Rettenmaier & Söhne GmbH + Co KG, Rosenberg, Germany) are natural, highly purified products, forming a completely insoluble fibre network. The cellulose-based fibres are made by a special method to achieve a very fine and defined particle structure. The so-called fibrillation technique produces fibres with high capillary effect and surface activity. Arbocel BWW 40 contains only cellulose. Controlled research has shown that incorporation of the cellulose preparation into chew treats ameliorates dental disease in dogs (Beynen et al., 2010) and that addition to the food reduces hair ball symptoms in cats (Beynen et al., 2011). Arbocel RC contains 46% cellulose, 24% lignin and 16% hemicellulose; the crude fibre content is 66%. The three studies described below demonstrate that inclusion of Arbocel RC in dog food improves digestion, reduces faeces volume and maintains optimum faeces consistency.
Fibrillated cellulose versus wheat bran
Within the framework of her PhD study at the Ludwig Maximilians University of Munich, Ludolph (2007) has used diets containing either wheat bran or Arbocel RC as fibre source. Wheat bran contains about 11% crude fibre. The main fibres in wheat bran are hemicellulose (about 28%), cellulose (about 8%) and lignin (about 5%).
Adult, female beagle dogs (n=16) with average weight of 12.2 kg were fed the two diets according to a cross-over design. On a group basis, faeces were collected quantitatively for 21 days. The dry foods were based on corn (42.5%) and chicken meal (14.5%). The control diet contained 15% wheat bran which was replaced by 2.7% Arbocel RC, 9.3% wheat flour and 3% greaves in the test diet. The diets contained 3.1 and 3.2% crude fibre. An individually determined amount of food was provided once per day.
Acceptance was similar for the two diets. Average weight of fresh faeces was computed as 147 g/day for the wheat-bran diet and 110 g/day for the diet containing Arbocel RC; measured dry matter contents of faeces were 27.6 and 29.0%, respectively. It was calculated that apparent dry matter digestibility was 2.3% units higher for the Arbocel diet. Faeces quality was scored on a 1-4 scale (1 = solid; 2 = optimally formed; 3 = pasta like; 4 = liquid). For the wheat-bran and the Arbocel diet the average faecal scores were found to be 2.3 and 2.2.
Another experiment comparing Arbocel RC with wheat bran was carried out by Shiva Kumar and colleagues (2012) at Provimi Animal Nutrition India. The control, extruded, dry food consisted of 69% cereals (wheat flour, wheat bran, corn gluten), 20% poultry meal, 6% fats and oils and 5% premixes. The test diet contained 3% Arbocel RC at the expense of wheat bran. The two diets were iso-nitrogenous and iso-energetic; the analysed crude fibre contents were identical (2.1%). The diets were fed to six adult dogs, weighing 30-42 kg. A cross-over design with periods of 10 days was used. Food was supplied once daily, the amount being equivalent to maintenance energy requirements. During the last five days of each period, faeces were collected.
Table 1 documents that the apparent digestibilities of dry matter, crude protein, crude fat and carbohydrates (nitrogen-free extract) were increased by consumption of Arbocel. The increases are statistically significant. Based on the mean values for amount of food supplied and dry matter digestibility, the faecal output of dry matter was calculated. For the control diet and the Arbocel diet, faecal excretion of dry matter was 169 and 149 g/day. When assuming a faecal dry matter content of 28%, the production of fresh faeces for the control and Arbocel diet would be 604 and 532 g/day.
Fibrillated cellulose versus beet pulp
At the Free University of Berlin, Kröger et al. (2011) fed eight Beagles dry foods with similar crude fibre content, but containing either sugar beet pulp or Arbocel RC. Dried beet pulp contains 12-18% crude fibre, but has a high content (about 20%) of soluble fibre in the form of pectin. The control diet contained 50% rice flour, 31% poultry meal and 12% beet pulp. The test diet contained 59.8% rice flour, 30.1% poultry meal and 2.7% Arbocel RC. The control and test diets contained 3.1 and 2.4% of crude fibre. The dogs received each diet for 8-12 weeks. The amount of faeces produced was determined daily. Faeces collected during the last five days of each feeding period were used to measure digestibility of macronutrients.
The Arbocel versus beet-pulp diet significantly reduced the amount of fresh faeces from 168 to 94 g/day and raised the faecal dry matter content from 29.7 to 42.3%. Thus, the output of dry faecal matter was reduced from 50 to 40 g/day. This indicates that Arbocel RC had increased the digestibility of dietary dry matter. Table 1 shows that the feeding of Arbocel RC instead of beet pulp increased the apparent digestibilities of dietary organic matter and crude protein; the differences are statistically significant. Fat digestibility was unaffected. Scores for faeces consistency, on a 5-point scale, were 2.1 and 2.3 for the control and test diet.
Volume and consistency
When feeding diets with similar content of crude fibre, the intake of Arbocel RC instead of wheat bran or beet pulp reduces fresh faeces output in dogs. The decrease ranged from 12 to 44% (Figure 1). The impact of dietary fibre type is the sum of the effects caused by the addition of one fibre source and omission of the other. The influence of Arbocel RC may be specific because it is seen in comparison with two different fibre sources. Arbocel is not digestible and poorly fermentable. Thus, ingested Arbocel is excreted and higher intakes induce higher faecal output. However, compared with other fibre types, Arbocel RC lowers faecal output and maintains optimum faeces consistency.
The Arbocel-induced lowering of faeces production is explained by the observed increase in dry matter digestibility, which in turn is caused by increased digestibility of protein, fat and carbohydrates. Low digestibility of the base diet appears to enhance the promoting effect of Arbocel on digestion. The mechanism by which Arbocel stimulates digestion is not known, but it could relate to the formation of specific networks in the intestinal content, leading to enhanced access of digestive enzymes to their substrates. Alternatively, wheat bran and beet pulp may inhibit digestion.
Pet food quality, as perceived by dog owners, relates to faeces volume and consistency. The three studies described here indicate that dietary fibre type is a determinant of faeces characteristics and digestive efficiency. This knowledge may be implemented in pet food formulation and production.
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