Effects of Dietary Protein Restriction on Colonic Microbiota of Finishing Pigs

Simple Summary Low-protein diets can effectively alleviate the pressure of protein resource shortage and nitrogen emission from the pig industry. In recent years, the effects of low-protein diet and amino acids or additives on growth performance, meat quality and odor emission of growing finishing pigs have been studied. However, gut health is also an important indicator, as well as whether the changes in intestinal flora caused by the reduction in dietary protein levels are beneficial to the growth of finishing pigs. Additionally, how will the metabolites of the microbes change when the microbes change in the hindgut? This study is aimed at the effects of low-protein diets with four amino acids balanced on serum biochemical parameters and colonic microflora of finishing pigs. Fifty-four healthy (Duroc x Landrace x Yorkshire) hybrid barrows with an average body weight of 70.12 +/- 4.03 kg were randomly assigned to one of three dietary treatments with three barrows per pen and six pens per treatment. The barrows were fed a normal protein diet (NP), a low-protein diet (LP), and a very low-protein diet (VLP). Compared with the NP diet, reduced dietary protein did not influence serum biochemical parameters (p > 0.05). The valeric acid was significantly increased with the VLP diet (p < 0.05). Compared with the NP diets, the abundance of Terrisporobacter (13.37%) Clostridium_sensu_stricto_1 (23.37%) and Turicibacter (2.57%) increased to 21.04, 33.42 and 13.68% in LP diets and 16.72, 43.71 and 14.61% in VLP diets, while the abundance of Lactobacillus (9.30%) and Streptococcus (25.26%) decreased to 3.57 and 14.50% in LP diets and 1.86 and 4.07% in VLP diets. Turicibacter and Clostridium_sensu_stricto_6 had a powerful negative correlation with the content of valeric acid (p < 0.01), while Peptococcus and Clostridia_UCG-014 had a very solid positive correlation (p < 0.01). In conclusion, reducing dietary protein level can improve colon microbiota composition, especially reducing the abundance of bacteria related to nitrogen metabolism, but has no significant effect on SCFA except valeric acid. In addition, reduction in the dietary protein level by 5.48% had more different flora than that of 2.74% reduction in dietary CP level.