Laboratory of Animal Nutrition, Ghent University, Heidestr. 19, 9820 Merelbeke, Belgium The effect of oligofructose and inulin on faecal characteristics and nutrient digestibility in healthy cats By M. HESTA, G. P. J. JANSSENS, J. DEBRAEKELEER and R. DE WILDE Summary The effects on faecal characteristics of different concentrations of oligofructose (0, 3, 6 and 9%) were investigated. The 6 and 9% supplemented groups differed signi®cantly compared with the control group in almost all faecal characteristics. There were no signi®cant differences regarding the macroscopical and chemical aspects of the faeces between the control and the 3% supplemented group. There was a trend for a lower pH of the faeces in the 3% supplemented group, suggesting a substantial effect on the faecal composition. In a second experiment, the effects of oligofructose (3%) and inulin (3 and 6%) on digestibility parameters were tested. In the supplemented groups the apparent protein digestibility was lower but this was due to a higher bacterial nitrogen content of the faeces. There were no signi®cant differences between 3% inulin and oligofructose, although oligofructose seemed to be more easily fermentable, because of a trend to a higher concentration of short chain fatty acids (SCFA) in the faeces of the oligofructose group. Introduction The important role of the intestinal gut ¯ora in host health has resulted in a lot of interest in manipulating the composition of that ¯ora, especially by the use of prebiotics. The concept of prebiotics was introduced by GIBSON and ROBERFROID (1995) as: `a nondigestible food ingredient that bene®cially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon and thus improves host health'. Fructo-oligosaccharides (FOS) are classi®ed as prebiotic (GIBSON and ROBERFROID 1995). Depending on the chain length, there is a distinction between oligofructose, with an average degree of polymerization of 4.8, and inulin, with an average degree of poly- merization of 12. Inulin is extracted from chicory roots using a hot water process. By controlled enzymatic hydrolysis of inulin, oligofructose is formed. Naturally high concentrations of oligofructose and inulin can be found, for instance, in garlic, onions, artichoke and asparagus (GIBSON and ROBERFROID 1995). HUSSEIN et al. (1998) analysed 25 pet food ingredients and found wheat by-products to contain the highest concentrations of total FOS (wheat bran: 4 mg/g dry matter). Possible bene®cial effects In the small intestine, the effect of inulin and oligofructose is probably minimal. They do not appear to increase viscosity, nor to bind bile acids. They may cause an increase in bulk and are soluble in water (SCHNEEMAN 1999). However, BUDDINGTON et al. (1999) noted that diets containing fermentable ®bres (a combination of beet pulp and oligofructose) J. Anim. Physiol. a. Anim. Nutr. 85 (2001), 135±141 Ó 2001 Blackwell Wissenschafts-Verlag, Berlin ISSN 0931±2439 Eingang des Ms.: 6. 9. 2000 U. S. Copyright Clearance Center Code Statement: 0931±2439/2001/8505±0135 $ 15.00/0 www.blackwell.de/synergy