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 colony-forming 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.

The effect of starch gelatinisation degree on intestinal morphology, intestinal pH and bacteriology in pigeons.

The effect of starch gelatinisation degree in extruded feed on intestinal morphology, intestinal pH and faecal bacteriology was investigated in pigeons. Extruded complete pigeon diets would offer the principle advantage of providing equilibrated nutrients and energy, but factors such as starch gelatinisation require investigation before these diets are offered as main dietary items to pigeons. Birds were fed two diets with equal ingredient composition and nutrient content, but with a different degree of starch gelatinisation resulting from altered extrusion processing (high gelatinisation degree (HG) with 73.6% gelatinisation vs. low gelatinisation degree (LG) with 53.1% gelatinisation). Feed intake and weight gain changes were measured weekly. Blood samples were collected at day 28 and analysed for non-esterified fatty acids, lactate dehydrogenase and glucose. The pH values for fresh excreta were measured; thereafter fresh excreta were collected and cultured for measurement of colony-forming units for bacterial classes. At the end, morphological measurements were examined and the pH values throughout the gastrointestinal tract were recorded. Liver, pancreas and abdominal fat were weighed. There was a tendency (p= 0.07) towards higher numbers of Escherichia coli in the excreta of the LG group compared with those in the HG group. No dietary treatment effects were noted on the number of Lactobacillus sp. in the excreta. In proximal parts of the intestine, LG revealed a significantly lower pH than HG. Villus height and crypt depth were not affected by dietary treatment, but the duodenum muscularis thickness, liver weight and pancreas weight were significantly lower in the LG than that in HG group. This trial demonstrated that the lower level of starch gelatinisation degree of extruded feed leads to acidification of the proximal gut and altered gut morphology in pigeons. Hence, extruded pigeon diets should preferably contain low-gelatinised starch instead of high-gelatinised starch. In addition, future research must focus on the effects of starch gelatinisation on the correlation between the intestinal pH, microflora content and intestinal morphology.

Effect of starch gelatinisation on nutrient digestibility and plasma metabolites in pigeons.

Feed manufacturing exerts physical and chemical changes in ingredients, including the gelatinisation of starch. Studies on the effect of the degree of starch gelatinisation on nutrient digestibility, metabolism and subsequent performance show inconsistent results, and no data are available in pigeons. In a cross-over trial, fourteen adult pigeons were randomly divided into two groups, in which two extruded pellet diets were tested. Both the diets were similar in ingredient composition and nutrient content, but differed in extrusion conditions, resulting in a different degree of starch gelatinisation: pellets with high gelatinisation degree (HG; 73.6% gelatinisation) and low gelatinisation degree (LG; 53.1% gelatinisation). After a 14-day adaptation period, all excreta were gathered per bird during a 5-day collection period. Coefficients of apparent digestibility of dry matter (DM), crude protein (CP), ether extract (EE), crude fibre (CF), crude ash (CA) and nitrogen free extract (NFE) as well as apparent nitrogen retention were calculated from proximate analyses of feed and excreta. Further, excreta consistency was subjectively scored. Blood samples were taken at the end of each period and plasma samples were analysed for glucose, fructosamine and triglycerides. Feed intake and body weight changes were recorded weekly. The apparent digestibility coefficients (ADCs) of DM, OM, CP, EE, CA and NFE were significantly higher in the LG group (p < or = 0.05). The ADC of crude fibre was numerically higher in the LG group but not significant, and no significant differences were found in starch digestibility. Excreta consistency score tended to be higher in the LG diet group. Neither plasma glucose nor plasma fructosamine values were significantly different between the two test diets. The results of this study show that lower degree of starch gelatinisation in extruded diets can enhance digestibility in pigeons.