4.2 Effects of different dietary protein levels on intestinal
microflora structure and KEGG functional predictions
Analyzing the structural composition of animal intestinal microbes can
reflect growth environments and diet to a certain extent [25]. In
one study, Zhou et al. [26] found that low-protein diets can
regulate microbial composition and metabolites in pig hindguts without
influencing growth performance although the potential effects of this
regulation on health remains unknown. Here, microbes in the jejunum and
cecum of Bamei pig were mainly shown to comprise representatives of
phyla Firmicutes and Bacteroidetes, although significant differences
were seen between groups at different protein levels. Representatives of
phylum Firmicutes in jejunum test group II samples occurred at
significantly higher proportions than those in test group I samples
(P = 0.020). Similarly, representatives of phylum Firmicutes in
caecum test group II samples also occurred at significantly higher
levels than in test group I (P = 0.034) while representatives of
phylum Bacteroidetes in test group I samples also occurred at
significantly higher levels than in test group II samples (P =
0.011). These outcomes show that reducing the protein level can have an
effect on the structure of the main flora of the phylum level. Indeed,
Firmicutes is also the dominant intestinal phylum present in the low
protein group, consistent with previous studies [13,27]. Dai et al
[28] showed that, at the genus level, bacteria in the jejunum of
Bamei pigs mainly comprise unidentified Clostridiales ,Terrisporobacter , and Turicibacter , while those in the
cecum mainly include unidentified Clostridiales ,Terrisporobacter , Turicibacter , and Streptococcus .
The main role of Streptococcus appears to be to utilize AA in the
intestine to synthesize bacterial proteins. In another earlier study,
Fan et al. [20] showed that as dietary protein levels decrease, the
abundance of Clostridium sensu stricto 1 in ileum samples
from pigs decreased significantly. The reason for the analysis is that a
decrease in dietary protein level causes a reduction in nitrogen source
as a fermentation substrate. The relative abundances ofTerrisporobacter in the diet group with a normal protein level
were also significantly higher than in the group fed a low protein
level; this genus is an emerging anaerobic pathogen but the few cases
published so far usually report it as a component of a multi-microbial
infection [29]. Similarly, Romboutsia occurred at a higher
level in the normal diet protein group than the low protein group. The
results of this study show that as dietary protein levels decrease, the
proportion of Lactobacillus in jejunum and cecum of microbial
floras also gradually increased. Dietary protein levels therefore exert
a certain influence on the composition of Bamei pig intestinal floras.
As dietary protein levels decrease, no significant differences in
abundance either the jejunum or caecum were seen although this change
can improve microbial composition. The outcomes of this study have also
enabled us to predict the KEGG functions of genes present in microbial
floras at different dietary protein levels. These results show that
genes extracted from jejunum and cecum microbes at different dietary
protein levels were mainly enriched in the ‘metabolism pathway’,
followed by ‘genetic-information-processing’, and
‘environmental-information-processing’ channels. In contrast, at Level2,
the main enrichment pathways are ‘membrane-transport’ and
‘carbohydrate-metabolism’. Enrichment pathways in jejunum and cecum
genes are significantly different in terms of the presence of
‘metabolism’ and ‘environmental-information-processing’; these results
indicate that an appropriate reduction in dietary protein can have a
beneficial effect on the metabolic function of microorganisms in the
intestine. A reduction can assist metabolic activities, consistent with
previous work [30–31].