Effect of temulawak (Curcuma xanthorrhiza) powder in reducing proteolysis in fermented total mixed ration with okara for ruminants

High protein content in silage feed often triggered excessive proteolysis caused by proteases derived from both plants and spoilage bacteria, which reduced the nutritional quality for ruminants. Temulawak (Curcuma xanthorrhiza) is an herbal plant with antibacterial and antioxidant properties, which have been reported to reduce proteolysis in previous studies. This study aimed to evaluate the effects of temulawak powder (TP) as an anti-proteolysis additive in the fermentation of total mixed ration-based okara silage (TMRO-silage) and its impact on silage characteristics. Additionally, the study examined the effects of drying temperature on temulawak extract optimization. Temulawak was dried at 50, 65, and 80°C, followed by the measurement of phenol, flavonoid, and ferric reducing antioxidant power (FRAP) content. The TMRO-silage was composed of commercial feed and okaras (1:1 w/w), supplemented with 0-1% temulawak in increments of 0.25% (5 treatments and 4 replications). Fermentation lasted for 14 days. Proximate and in vitro analyses (control vs. temulawak treatments) were conducted to assess silage quality. Drying temulawak at 65°C significantly (P < 0.01) increased phenol (16.9 µg quercetin equivalent, QE), flavonoid (23.3 µg QE), and FRAP (30.1 µg QE) content per dry weight. Temulawak supplementation significantly reduced ammonia levels and increased the crude protein content of TMRO-silage (P < 0.01). Moreover, it decreased ammonia concentration in the rumen (P < 0.01), improved dry matter and organic matter digestibility (P < 0.05), and notably reduced methane production per total gas volume (P < 0.05). In conclusion, temulawak effectively preserves the quality of complete feed silage, enhances rumen metabolism, and mitigates methane emissions.