1 INTRODUCTION
The animal intestine is the main place where nutrients are digested. A
body provides microorganisms with the nutrients they need for growth via
the intestine; microorganisms in intestines decompose food materials and
produce smaller molecules that the host organism can digest and absorb.
Microorganisms in the guts of animals are therefore mutually beneficial
[1,2]; a large number of microorganisms live in animal intestines,
reaching a total such that the number of microbial cells exceeds other
components [3]. Microorganisms influence host growth, development,
nutrient absorption capacity, and intestinal immunity and play a vital
role in health [2]. In earlier work, Kim et al. [4] showed that
intestinal microorganisms exert a certain promotional effect on animal
body growth and development and participate in digestive immune
functions. Intestinal microbial diversity therefore exerts an important
impact on microbial flora stability. In other words, the higher the
diversity, the more stable a flora will be and so the healthier the
animal gut. The microbial ecosystem of a pig gastrointestinal tract is
influenced by numerous factors but changes in dietary structure are
thought to be amongst the most important. The amount and quality of
protein in a diet exerts a significant influence on microbial community
structure in an intestine [5]; indeed, an intestinal flora seems to
be sensitive to source changes in dietary protein. In one example, the
use of highly digestible protein sources has been shown to reduce
fermentation and the growth of potentially pathogenic species [5].
Similarly, Fan Peixin et al. [6] showed that reducing dietary
protein levels by just 3% can increase ileal microbial diversity in
fattening pigs and, indeed, when this level is reduced by another 3%,
microbial diversity is significantly reduced. In another study, Chen
found that restricting 15% of dietary protein can increase the ratio of
beneficial microorganisms to harmful bacteria and optimize the structure
of the intestinal microbial community [7]. It is clear that dietary
protein level plays a very important role as a component of pig
production. A correct level not only provides the body with the
nutritional effects of amino acids (AA) necessary for endogenous protein
synthesis but also participates in regulating feed intake, lipids, and
glucose metabolism to maintain growth, development, biological
proliferation, digestive enzymes, and hormone secretion in the intestine
[8-10].
The demand for protein feed is very large throughout pig production.
Indeed, in order to reduce heavy nitrogen emissions into the
environment, protein levels should be reduced to promote the sustainable
development of this industry [11–12]. Protein levels fed to Bamei
pigs were reduced in this study by around 2% and 4% compared with the
base protein level of 16%, while essential AA were supplemented. The
effects of dietary protein levels on the intestinal microflora of Bamei
pigs was studied in order to provide a theoretical basis for further
enhancing the production of this species.