Puerarin in Ruminant Nutrition: From Rumen Microbial Modulation to Metabolic and Production Responses

Puerarin is the principal C-glycosidic isoflavone of Pueraria lobata, a legume long used as food and medicine, and has recently attracted interest as a plant-derived feed additive for ruminants. Research on puerarin in ruminant nutrition has expanded quickly, yet the findings remain scattered across in vitro cultures, feeding trials and mechanistic studies in non-ruminant models. This review follows the chain of events that begins when puerarin enters the rumen. Puerarin is degraded rapidly in rumen fluid in vitro (approximately 70% within 6 h) and is converted by the microbiota through isomerisation to daidzin, deglycosylation to daidzein and, potentially, reduction to equol, so that the parent compound is not the only bioactive species present. These transformations are accompanied by selective shifts in the abundance of taxa such as Veillonellaceae, Prevotella and Succiniclasticum, and by changes in fermentation output, most consistently an increase in microbial crude protein concentration and a shift in the volatile fatty acid profile towards propionate. Methane decreased in the single in vitro study that measured it, and the ammonia nitrogen response varied between studies. Beyond the rumen, puerarin and its metabolites have well-documented antioxidant, anti-inflammatory and barrier-protective effects in other species, acting through Nrf2, NF-κB and NLRP3 signalling, and these effects are relevant to rumen epithelial integrity and to post-ruminal tissues when protected formulations are used. Reported consequences for growth, meat and milk quality are promising but inconsistent. This review evaluates the strength of evidence for each link separately, identifies where causality has not been established, and outlines the dose, formulation and validation studies needed before puerarin can be recommended as a feed additive.