In vitro evaluation of ammoniation-fungal fermentation of citronella straw: Impacts on digestibility, ruminal fermentation, and palatability in Indonesian native sheep.

Background and Aim: Citronella straw (Cymbopogon nardus L.), a byproduct of essential oil extraction, is rich in lignin therefore poorly digestible, which limits its use as livestock feed. This study examined the impact of ammoniation and fungal fermentation using Pleurotus ostreatus, Trichoderma harzianum, and Aspergillus niger on the nutritional value, digestibility, and palatability of citronella straw for ruminants. Materials and Methods: Six treatments were evaluated in vitro with five replications: Ammoniated citronella straw (CsA), citronella straw fermented with P. ostreatus (CsFP), citronella straw fermented with A. niger, ammoniated and fermented with T. harzianum (CsAFTh), ammoniated and fermented with P. ostreatus (CsAFP), and ammoniated and fermented with A. niger. Samples were analyzed for proximate composition, fiber fractions, phenolic content, in vitro digestibility, and rumen fermentation parameters (pH, ammonia, volatile fatty acids, and methane). Palatability of selected treatments (CsAFTh vs. CsAFP) was tested in 18 Ettawa goats (18 months; 22.4 ± 5.5 kg). Results: The CsAFP significantly enhanced nutritive value, reducing acid detergent fiber (63.3% in CsA to 53.9%) and acid detergent lignin (15.7% in CsA to 11.4%), while increasing crude protein (9.1% vs. 6.4%-8.4%). Dry matter digestibility improved by 10%-12% (p < 0.0001). Rumen fermentation showed increased propionate, reduced acetate: propionate ratio, and CH4 reduction of 0.5 mmol/L. Palatability testing revealed higher voluntary feed intake for CsAFP (98 g at 360 min) compared with CsAFTh (36 g). Conclusion: CsAFP most effectively improved the nutritional quality, digestibility, and palatability of citronella straw. This strategy reduces lignin, enhances fiber utilization, shifts fermentation toward propionate, and decreases CH4 emission, supporting its potential as a sustainable feed for smallholder ruminant production. Further in vivo studies are warranted to confirm long-term performance, safety, and field applicability.