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Background and Aim: Enteric methane emissions from ruminants represent a major loss of dietary energy and contribute significantly to greenhouse gas accumulation. Phytogenic feed additives and lipid supplements have emerged as sustainable strategies to modulate rumen fermentation and mitigate methanogenesis. This study evaluated the synergistic effects of Piper ornatum (PO) leaf powder and lemuru fish oil (LFO) on in vitro rumen fermentation characteristics, nutrient digestibility, and methane reduction. Materials and Methods: A 4 × 4 factorial randomized block design was used, with four levels of PO (0%, 3%, 6%, and 9%) and LFO (0%, 1.5%, 3%, and 4.5%), and three replications. The basal diet was incubated with buffered rumen fluid for 48 h at 39°C. Parameters measured included microbial protein synthesis (MPS), protozoa population, partial and total volatile fatty acids (VFAs), ruminal pH, ammonia (NH₃) concentration, total gas production, methane production, and nutrient digestibility (dry matter, organic matter, crude protein, and fiber fractions). Results: The combined supplementation significantly influenced rumen fermentation (p < 0.05). Methane production and total gas output decreased markedly with increasing additive levels, with the lowest methane value (7.46 mL/g DM) observed at 6% PO and 4.5% LFO. Protozoa populations declined, indicating antimethanogenic effects. In contrast, MPS (up to 405.47 mg/100 mL), total VFA concentration (up to 123.51 mM), and NH₃ production increased significantly, reflecting enhanced microbial activity and nitrogen utilization. Nutrient digestibility, including dry matter, organic matter, crude protein, and fiber fractions, improved significantly across treatments. Ruminal pH remained stable (6.90–6.99), indicating no disruption of the fermentation environment. Conclusion: The combination of 6% PO and 4.5% LFO provided the most favorable balance between methane mitigation, fermentation efficiency, and nutrient utilization. This synergistic strategy integrates phytogenic bioactive compounds and polyunsaturated fatty acid-mediated hydrogen diversion, offering a promising approach for sustainable ruminant production. However, in vivo validation is required to confirm long-term effectiveness under practical feeding conditions. Keywords: essential oils, methane mitigation, nutrient digestibility, Piper ornatum, polyunsaturated fatty acids, rumen fermentation, sustainable livestock, in vitro.
Zain et al. (Tue,) studied this question.