Particle size distribution and solubility of dietary fibre in swede- (Brassica napus) based and wheat-bran-based diets during gastrointestinal transit in the pig

Abstract

Changes in fibre solubility, particle size and distribution and microbial activity during gut transit in pigs fed either a swede-based or wheat-bran-based diet were monitored. Digesta samples recovered from the stomach, ileum and caecum, together with feed and faecal samples, were examined for changes in the chemical and physical properties of the fibre fraction. Solubility of swede fibre was increased in the upper gut where a fourfold reduction in particle size and change in particle size distribution also occurred. This was associated with a loss of pectic polysaccharide. Little change in bran properties was noted in the foregut although the shape of bran particles was modified in the large intestine. Overall loss of the fibre fraction during gut transit was 41-5% for bran and 87-8% for swede. Microbial colonisation of the upper gut was significant on both diets. Chemical conditions during transit were thought to predispose pectic polysaccharides to solubilisation, and to encourage tissue maceration and hence particle size reduction. Lack of pectic polysaccharides in wheat bran and/or lignification maintained particle integrity in this diet. These properties may be important in influencing the physiological response to fibre in the diet.