In Vitro evaluation of lemuru fish oil supplementation and feed additives on rumen fermentation characteristics and fatty acid profile

Abstract

Methane (CH₄) emissions from ruminant fermentation represent both an environmental issue and an energy loss for animals. Previous studies have shown that Uncaria gambir extract and direct-fed microbials (DFM) can each reduce methane production and improve rumen fermentation. This study aimed to evaluate the combined effects of 1% Uncaria gambir or 0.5% DFM, at different levels of lemuru fish oil, on rumen fermentation and nutrient digestibility under in vitro conditions. The experiment used a basal substrate consisting of 30% Napier grass (Pennisetum purpureum), 30% Gliricidia sepium, and 40% concentrate (DM basis). Six treatments were applied: DFM (0.5%) combined with 1%, 2%, and 3% lemuru fish oil, and Uncaria gambir (1%) combined with 1%, 2%, and 3% lemuru fish oil. Results showed that supplementation significantly affected rumen fermentation, nutrient digestibility, methane production, microbial protein synthesis, and fatty acid profiles (P < 0.05). The combination of 0.5% DFM + 1% lemuru fish oil (P1) produced the highest dry matter digestibility (69.05%) and organic matter digestibility (72.42%), while also resulting in the lowest methane production (23.57 mL/g digested DM). In contrast, the combination of 1% Uncaria gambir+ 1% lemuru fish oil (P4) produced the highest total volatile fatty acid concentration (145.01 mM). In conclusion, supplementation of 1% lemuru fish oil combined with either 1% Gambier or 0.5% DFM produced the most favorable overall responses in rumen fermentation and fatty acid profiles, while the lowest methane production was observed at the 1% lemuru fish oil supplementation level under in vitro conditions.