Enteric methane production from ruminants represents an important source of greenhouse-gas emissions and also reflects a loss of dietary energy from the animal. The use of plant-derived phytogenic feed additives has received increasing attention as a natural strategy for modulating rumen fermentation while maintaining feed utilization. The present study was designed to evaluate a novel polyherbal feed additive comprising papaya (Carica papaya) leaves, coriander (Coriandrum sativum) seeds, cumin (Cuminum cyminum) seeds and fennel (Foeniculum vulgare) seeds for its effects on in-vitro rumen digestibility, fermentation characteristics and methane production. The selected plant materials contain diverse phytochemicals, including phenolics, flavonoids, enzymes and volatile bioactive compounds, which may influence rumen microbial activity and fermentation pathways. The polyherbal combinations will be evaluated at different inclusion levels using an anaerobic in-vitro rumen fermentation system. Total gas production, methane production, in-vitro dry matter digestibility, organic matter digestibility, pH, ammonia-nitrogen, short-chain fatty acids and microbial protein synthesis will be assessed to determine the overall fermentation response. Particular emphasis will be placed on identifying an inclusion level that suppresses methane production without adversely affecting substrate degradation and fermentation efficiency. The study is expected to provide information on the potential synergistic action of papaya, coriander, cumin and fennel as a natural phytogenic feed additive. The findings may contribute to the development of sustainable dietary strategies for improving ruminal nutrient utilization while reducing methane emissions from ruminant production systems.