Licorice extract modulates immunity,enhances beneficial microbiota,and alleviates lung pathology in PRRSV-positive pigs:optimizing the dose and administration route
摘要
Porcine reproductive and respiratory syndrome virus(PRRSV)is a major immunosuppressive pathogen involved in the porcine respiratory disease complex.Licorice extract(LE)has anti-inflammatory,immune-regulating,and growth-promoting effects.In this study,the use of LE as a novel feed additive in PRRSV-infected nursery pigs was evaluated,and the effects of dietary supplementation and drinking water were compared.A total of 264 weaned piglets were allocated into 8 groups:three dietary supplementation groups(low,medium,and high doses:BLL,BLM,and BLH),three drinking water supplementation groups(low,medium,and high doses:WLL,WLM,and WLH),a farm control group(Farm),and a negative control group(CON).Compared with the CON group,dietary LE supple-mentation in the BLL and BLM groups significantly increased the average daily gain(ADG)by 1.02-fold and 1.18-fold(P＜0.001)and reduced the feed-to-gain ratio(F/G)by 3.58％and 5.35％(P＜0.05),respectively,compared with their drinking water counterparts,with the effects in the BLM group being the most pronounced.Additionally,com-pared with CON,LE administration via either route alleviated coughing,with significant downregulated(P＜0.001)of cough scores in the BLH,WLL,and WLH groups during weeks 3-4.Furthermore,compared with the CON group,the BLM group exhibited increased tracheal cilia integrity(P＜0.1)and significantly decreased(P＜0.05)lung injury scores.While LE did not alter PRRSV-specific antigen or antibody levels(P=0.065),it significantly modulated immune responses by downregulating IL-1β and IL-6(P＜0.05),upregulating IL-10(P＜0.05),and increasing IgA,IgG,and IgM levels(P＜0.05).Gut metagenomic analysis revealed that LE notably increased the abundance of multiple beneficial bacteria and reshaped the structure of the gut microbiota.Specifically,LE upregulated Anaeromassilibacillus sp.An172 and reversed the antibiotic-induced decrease in the abundance of Bacteroides bouchesdurhonensis and Bac-teroides sp.OF04-15BH.These findings demonstrate that dietary LE,at an optimal dose of 2.6 g/kg,is a promising feed additive for PRRSV-infected pigs,with benefits mediated through immune modulation and gut microbiota remodeling.
