| Intestinal microflora plays an important role in animal growth and health. The diet is the main factor for both growth performance and intestinal flora. The protein is one of important nutrients that are essential for growth and intestinal flora. However, what are the effects of different dietary protein sources such as soybean, zein and animal protein on intestinal microflora? What are the effects of different dietary protein sources on microbial quantity and ratio of primary bacteria (eg: Lactobacillus) and what are the effects of different dietary protein sources on weaning piglets growth performance, intestinal flora and amino acid transport? All these questions remain to be studied. Therefore, this study was conducted to answer above questions. Firstly, the effects of different dietary protein sources on cecal microflora in SD rats were investigated; then, the effects of different dietary protein sources on growth performance, gut health and amino acid transport in weaned piglets were researched; thirdly, the effects of selected soya isolate protein and zein diet supplemented with amino acids on intestinal microflora and amino acid transport in weaned piglets were evaluated.Experiment 1:Effects of different protein sources on cecal microflora and metabolites of SD ratsTo determine the effects of different dietary protein sources on cecal microflora and metabolites in monogastric animals, one hundred SD rats were randomly assigned into 5 diet treatments. Diets were respectively formulated with casein, soya protein isolate (SPI), and zein as the only protein source, and Nitrogen free diet (NFD) as well as combined protein (COM) (SPI:casein: zein=65:25:10) diet were applied as controls. All rats were fed for 14 days. The results showed that casein significantly increased the number of total bacteria, Lactobacillus, Bifidobacterium and Bacillus in cecum contents of rats, and significantly lowered the number and ratio of E. coli, and increased the concentrations of microorganism metabolic products:acetic acid, propionic acid and butyric acid. The COM and SPI treatments were lower than casein treatment in the effect of promoting probiotics. The effect of promoting probiotics in zein treatments and NFD were lower than other treatments. The treatment of SPI significantly increased the number arid ratio of E.coli. The treatment of zein was worst in the effect of promoting the role of probiotics, the possible reason might be the unbalance amino acids of zein protein.Experiment 2:Effects of different protein sources on intestinal microflora and intestinal health of weaned pigletsThe aim of this experiment was to approach the effect of different proteins on intestinal microflora, intestinal health and intestinal environment in weaned piglets. Thirty-six piglets were randomly allotted into 6 treatment groups with 6 replicates in each. The SPI, casein, zein and COM were applied as protein source. Regular corn-soybean diet and N-free diet were used as control groups. The trial was conducted for 14 days. The results showed that:1. The treatment of casein was higher than SPI and zein treatments in ADG, and was lower than SPI and zein treatments in F/G. The treatment of zein was lowest in 6 treatments. The ADFI of normal treatment was higher than other treatments.2. The treatments of casein and normal increased the VFA in the cecum, colon and rectum contents of weaned pigs. Zein treatment increased the VBN of cecum, colon and rectum. The SPI treatment was between zein and casein treatment.3. The effects of casein, normal and COM treatments on enzyme activities (units/mg prot) were higher than other treatments in the weaned pigs. The trend was consistent with the performance.4. The serum albumin, globulin and total protein content in the normal, casein and COM treatments were the highest among all groups, and these in the soy protein isolate and zein group were lower. The lowest was NFD treatment. The serum urea nitrogen was higher in zein and SPI treatments. There is no significant different in the serum cytokines IL-2, IL-6 among groups. SPI increased serum TNF-αconcentration.5. The pH-value of zein and NFD treatments was higher than other treatments in all parts of gastrointestine (stomach, duodenum, jejunum, ileum, cesium and colon). The pH-value of casein, COM and normal treatments were lower than other treatments.6. Protein and amino acid digestibilities of casein and normal treatments were higher than other treatments. Zein treatment was lower than other treatments. The trend was consistent with the performance. The possible reason might be the imbalance amino acids of zein.7. Casein, normal and COM treatments significant increased the height of villus and increased the ratio of villus to crypt depth. The crypt depths were not significantly different among groups.8. The expression of amino acid and peptide transportation related genes in casein and normal treatments were higher than other treatments. There was no significant difference in CAT-1 mRNA expression among all treatments. The expression of amino acid and peptide transportation related genes in zein and NFD treatments were lower than other treatments. The expressions of IGF-1 mRNA in casein and normal treatments were higher than other treatments.9. The treatments of normal and Casein significantly increased the number and ratio of Lactobacillus, Bifidobacterium and Bacillus, and significantly reduced the number and ratio of E.coli. The treatment of SPI significantly increased the number and ratio of E.coli. The possible reason was that SPI contained antigen and increased diarrhea of weaned piglets.Casein could enhance the performance of weaned piglets, reduce intestinal pH value, maintain intestinal morphology of health, and increase the number as well as the scale of beneficial bacteria in the intestines. However, the plant protein especially zein impaired the intestinal health and blunted the growth of beneficial bacteria in the gut.Experiment 3:Effects of different protein sources on intestinal microflora and intestinal health of weaned piglets after amino acids supplementation.The aim of this experiment was to approach the effect of different proteins supplemented with amino acid on intestinal microflora, intestinal health and intestinal environment of weaned piglets. Thirty-six piglets were randomly allotted into 6 treatment groups with 6 replicates each. The trial was conducted for 14 days. The results showed that supplementation of amino acids promoted intestinal environment, intestinal health and intestinal microflora, but the improvement was lower than the treatment of casein. CHOP was an important marker indicating the balance of amino acids. The expression of CHOP mRNA was lower after supplementing amino acid to zein diet, which suggested the balance of amino acids was improved after amino acids supplementation in zein diet.In summary, effects of different proteins on intestinal microflora in weaned piglets were distinct. Casein could effectively increase intestinal Lactobacilli, Bifidobacteria and Bacillus, and reduced the number of E. coli. The effect of SPI was between casein and zein treatments. Zein treatment was the worst one. Effect of plant protein was improved after amino acid supplementation on intestinal microflora in weaned piglets. The supplementation of amino acids could partially improve plant protein quality.
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