Indirect evidence for microbiota reduction through dietary mannanoligosaccharides in the pigeon, an avian species without functional caeca

A feeding trial was conducted to evaluate the effects of mannanoligosaccharides (MOS) on nutrient digestibility, intestinal pH, gut morphology and faecal bacteriology of pigeons, as model for birds without functional caeca. Sixteen adult pigeons (Columba livia domestica) were randomly allotted to either an extruded pellet diet with or without 0.4% MOS. After an adaptation period of 24 days, excreta were collected during 4 days. Apparent nutrient digestibility coefficients were determined using total collection method. Further, excreta pH was measured and percentage of uric acid determined. Fresh excreta were cultured for measurement of colonyforming units for Escherichia coli. At the end, the gastrointestinal tract (GIT) was excised and pH measurements performed on the separate GIT sections. Finally, pancreas, liver, gizzard and abdominal fat pad were weighed, and standardised segments of duodenum and jejunum were removed for microscopic measurement of crypt depth, villus height and muscularis thickness. Feed intake and water intake were similar between control diet and MOS diet. Intestinal pH was unaffected by MOS supplementation; however, excreta pH was significantly lower in pigeons on the MOS diet. Although nutrient digestibility was similar between treatments, uric acid content of excreta was significantly higher in the MOS group in relation to the control group. Further, duodenal crypt depth, villus height and muscularis thickness, as well as jejunal muscularis thickness were all significantly reduced by MOS supplementation. No effect of MOS supplementation was seen on the counts of E. coli. Furthermore, despite marked differences on both GIT morphology and uric acid content of excreta, apparent digestibility coefficients, and organ weights, were similar between treatments. It is suggested that the MOS-induced changes on gut morphology and the reduced excreta pH reflect a reduced bacterial challenge in the intestine of pigeons. Supplementation of MOS, therefore, has potential as prebiotic strategy in birds without functional caeca