Lactococcus G423 Ameliorates the Growth Performance of Broilers by Modulation of Gut Microbiota- Metabolites

This study aimed to explore whether Lactococcus G423 could ameliorate growth performance of broilers by modulation of gut microbiota-metabolites based on the 16S ribosomal RNA (rRNA) and liquid chromatography-mass spectrometry (LC-MS). A total of 640 one-day-old AA broilers were randomly divided into 4 groups (Control (CON), Lac_L, Lac_H, and ABX). Average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were calculated on the 42nd day. The ileum content was harvested and immediately frozen in liquid nitrogen for 16S rRNA and LC-MS analyses. Then, the results of 16S rRNA analysis were confirmed by quantitative polymerase chain reaction (qPCR). Compared with the CON group, ADG significantly increased in the Lac_H group (P<0.05), and survival rate significantly decreased in the Lac_H, Lac_H, and ABX groups (all P<0.05). A significant difference in microbial diversity was found among the four groups. Compared with the CON group, the abundance rates of Firmicutes and Lactobacillus in the Lac_H group were significantly risen (P<0.05). The global and overview maps and membrane transport in the Lac_L, Lac_H, and ABX groups significantly changed versus those in the CON group (P<0.05). The results of LC-MS demonstrated that Lactococcus could significantly improve the levels of some metabolites (6-hydroxy-5-methoxyindole glucuronide, 9,10-DiHOME, carbamazepine-O-quinone, N-Acetyl-L-phenylalanine, and kynurenine), and these metabolites were involved in 5 metabolic pathways. Among them, the pathways of linoleic acid metabolism, phenylalanine metabolism, and pentose and glucuronate interconversions significantly changed (P<0.05). Lactococcus improved wight and survival rate of broilers through the gut microbiota, regulating the pathways of amino acid metabolism, lipid metabolism, bile acid metabolism, and carbohydrate metabolism. However, antibiotics may negatively influence the gut microbiota. IMPORTANCEImprovements in the growth rate of broiler chickens can be achieved through dietary manipulation of the naturally occurring bacterial populations while mitigating the withdrawal of antibiotic growth promoters. Lactococcus is industrially crucial lactic acid bacteria, can be incorporated into the diets of chickens to improve their growth performance. This study investigated the key mechanisms behind this progression and pinpointed Lactococcus improved wight and survival rate of broilers through the gut microbiota, regulating the pathways of amino acid metabolism, lipid metabolism, bile acid metabolism, and carbohydrate metabolism.