Relationship between gut microbial species and energy metabolism in broiler chickens
Gastrointestinal microorganisms have a highly significant impact on uptake and utilisation of energy and other nutrients and on the response of poultry to anti-nutritional factors (such as non-starch polysaccharides), pre- and pro-biotic feed additives and feed enzymes.
Current methods for analysis of intestinal flora rely on culturing, which is not only laborious but may miss a large part of the uncultivable microflora. Alternatively, DNA techniques have the advantages of being rapid, relatively inexpensive and capable of monitoring gene regions of complex populations.
To this end, terminal restriction fragment length polymorphism (T-RFLP), a microbial profiling technique for examining the chicken intestinal microflora based on high-throughput, high resolution fingerprinting of bacterial gene regions has been developed and is being used to monitor diet induced changes. This tool will help provide insight into how gut microflora may impact on poultry health and nutrition. T-RFLP was used to examine changes in gut microbial communities in response to addition of enzyme product to a barley-based diet to increase apparent metabolisable energy (AME).
Total nucleic acid was extracted from chicken gut samples by a modification of a SARDI proprietary extraction method. Bacterial ribosomal DNA was amplified with universal 16S bacterial primers, one of which was 5Â¡Ã¤-labelled with 6-carboxyfluorescein. Amplicons were cut with a four base pair recognition sequence restriction enzymes and separated on a capillary DNA sequencer. Data were analysed using GeneScan 3.7 (Applied Biosystems) to determine positions of terminal restriction fragments (TRF).
Prior to statistical analysis the TRF profiles were analysed by a modified method of Dunbar et al., 2001 and resulting TRF treated as operational taxonomic units (OTU). OTU were analysed using multivariate statistical models (Primer 5, Primer-E Ltd., Plymouth UK).
Forty-eight broiler chickens were separated into two groups of twenty-four and raised on a barley diet and a barley diet supplemented with exogenous enzyme product.
Digesta and gut sections were taken from the ilea of each chicken and the microbial community analysed by T-RFLP. The apparent metabolisable energy (AME) values of barley-based diets with and without feed enzyme product were determined in a classical AME study involving measurements of total feed intake and total excreta output and subsequent measurement of gross energy values of feed and excreta.
The most significant difference between the two treatments is the presence of a taxonomically related group and/or species at an OTU of 521 in the barley diet group, which is insignificant in the barley plus enzyme diet group. Using sequence data obtained from chicken gut bacterial isolates it is possible to extrapolate that the OTU at 521 represents Clostridium perfringens.
This would be consistent with other research indicating that the addition of exogenous enzyme to the diet reduces C. perfringens growth.
Multivariate statistical analysis of OTU's from the two treatments showed that there is a significant difference in the overall ileal microbial communities of chickens fed a barley versus barley plus enzyme diets.
Classical growth/performance analysis showed that chickens fed a barley plus enzyme diet had a significantly higher AME than chickens on the control barley diet. Overall, metabolic energy was increased and variability was reduced in the diet containing exogenous enzyme, which are consistent with many previous reports.
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Article made possible through the contribution of the Australian Poultry Science Symposium (APSS) 2006.