Interrelationship of Diet Fibre and Endoxylanase With Bacteria in the Chicken Gut

by Fischer, Eva Nancy

Abstract (Summary)
Four trials were conducted to assess the influence of non-starch polysaccharides (NSP) from dietary corn (C), wheat (W) and wheat supplemented with endoxylanase (E) on performance, the gastrointestinal tract and on the bacterial population and its fermentation characteristics in broiler chickens. Trial one determined the difference in GIT size, specific culturable intestinal bacteria numbers, and volatile fatty acid (VFA) production at 42 d between C, W and wheat diets supplemented with E either throughout the 42 d or for 0-28 d or 29-42 d. The second trial utilized the same wheat treatments as the first trial, but GIT and VFA measures were taken at 14, 28 and 42 d while bacterial enumeration was only done at 28 and 42 d. This experiment was analyzed as a two-way analysis of variance with age and treatment effects. A third trial evaluated the C, W and E diets for differences in the amounts of total aerobic and anaerobic bacteria cultured at 28 and 42 d. The fourth trial was a two-way analysis of variance evaluating the effect of age and diet (C, W and E) on performance, GIT size, VFA production and residual NSP in the terminal ileum at 7, 14, 21, 28, 35 and 42 d. Performance was measured in all four trials and digesta viscosity was measured in all but the third trial.

Results from the first trial showed that E supplementation of wheat diets improved performance. Viscosity was lowest for C diets. Measures of GIT size were all smaller on C versus wheat-based diets. Ileal anaerobes tended to be higher with E than without while caecal anaerobes were higher on unsupplemented wheat diets. VFA production was higher for wheat versus corn fed birds in the ileum. C diets and wheat diets where E was removed at 28 d yielded the highest caecal propionic acid levels.

In the second trial, performance was also improved with E supplementation. Viscosity was lower for E supplemented wheat-fed birds than unsupplemented birds, except at 42 d. Full ileal weights were higher for W diets versus all others while caecal weights were lower on this diet. Bacterial data indicated higher levels of ileal anaerobes and some caecal anaerobes on W diets at 28 and 42 d. VFA content of the digesta, at 28 d was higher in the ileum in diets without E and the same tendency was noted for caecal VFA. At 42 d ileal VFA production was higher with E and caecal VFA production was higher without E. The results from the first two trials demonstrate that while certain anaerobic bacteria do increase in the ileum of W diets, others appear to respond to the substrates created by E supplementation in both the ileum and the caecum. Age related adaptation also appears to affect the response of the bacteria to E supplementation.

In the third experiment C and E birds performed equally well with W birds having the highest gain to feed ratios after 14 d and overall. E diets resulted in the highest numbers of caecal anaerobes with C birds having the lowest number. At 42 d, birds had higher numbers of caecal anaerobes than at 28 d. At 28 d, caecal aerobes were highest on E diets (P<0.10) while at 42 d, caecal anaerobes were lowest on the C diet and similar for the two wheat diets. Therefore, despite performance similarities between C and E birds, there were definite differences in the bacteria present in the hindgut on each diet. This is likely due to the difference in residual dietary substrate in the hindgut of the birds fed different diets and its ability to enter the caeca. The substrates present in the ileum of E birds may be of benefit to both the bird and to the different cross-section of caecal bacteria present. Less NSP substrate is likely to be available in the hindgut of C birds.

Results from the fourth trial showed that performance was equivalent across treatments. Jejunal viscosity was highest (P<0.05) for the W diet at all ages except 7 d. Ileal viscosity was highest in this diet at all ages. Jejunal and ileal weights as a proportion of body weight were generally largest for W followed by E, and smallest for C. Caecal lengths followed the same pattern but caecal weights were highest for E. Ileal VFAs were not affected by treatment. Caecal acetic acid was highest for birds fed W and E diets, whereas caecal pH, propionic, isobutyric, isovaleric and valeric acids were highest for C birds. There was a significant interaction between diet and age for propionic acid. E diets had the highest (P<0.001) amounts arabinose and xylose from soluble and low molecular weight NSP present in ileal contents. As the birds aged, proportionally more arabinose and xylose was solubilized from the W diet. The E diet yielded higher, but relatively steady levels of soluble arabinose and xylose whereas the C diet yielded the lowest levels and no change was seen with age. This suggests a bacterial adaptation to wheat NSP with age of the bird and the presence of NSP resistant to ileal bacterial hydrolysis in C diets.

It is concluded that the higher NSP content of the wheat diets is likely associated with the increased GIT size of the wheat-fed birds. While the NSP in these diets are broken down by the caecal bacteria to acetate and butyrate, the corn diet resulted in the production of propionate and isovalerate. The latter finding suggests that undigested starch and protein from corn enter the caeca and are being fermented by bacteria in this location. All of the differences in bacterial composition, fermentation and substrates provide evidence for changes in dietary NSP content and structure having a significant impact on changing the bacterial profile of the GIT of the broiler chicken.

Bibliographical Information:

Advisor:Estrada, Alberto; Laarveld, Bernard; Classen, Henry L.

School:University of Saskatchewan

School Location:Canada - Saskatchewan

Source Type:Master's Thesis



Date of Publication:10/22/2008

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