In Vitro Rumen Fermentation and Digestibility Characteristics of a Goat Diet Supplemented with Raw Propolis from Four Stingless Bee Species

The effectiveness of rumen fermentation controls the extent of feed utilization by ruminants. However, part of the feed energy is lost as methane (CH4), a greenhouse gas. Stingless bee (Galo-galo) propolis is a potential natural feed additive for modulating rumen fermentation, but its function in the rumen has not been widely studied. This study evaluated the effects of raw propolis supplementation from four stingless bee species (Heterotrigona itama, Tetragonula minangkabau, Tetrigona binghami, and Geniotrigona thoracica) on gas production, digestibility, and rumen fermentation characteristics in goats in vitro. A completely randomized design with five treatments (one control and four propolis sources at 3 g/kg DM) and six replications was used. Propolis supplementation did not significantly affect total gas production, CH4, pH, ammonia, protozoal population, or dry matter, organic matter, and crude protein digestibility compared with the control (P>0.05), indicating that this dose did not impair rumen fermentation. Total VFA differed significantly (P<0.05) among treatments, being highest with G. thoracica and lowest with T. binghami, the only source that reduced total VFA relative to the control. Although CH4 output itself did not differ among treatments, individual-level Pearson correlation analysis showed a strong negative association between CH4 and propionate (r = -0.847; P<0.001); because CH₄ was estimated stoichiometrically from VFA proportions, this association is consistent with, but does not independently demonstrate, hydrogen competition between propionate formation and methanogenesis. These findings show that raw Galo-galo propolis did not impair in vitro rumen fermentation at the tested dose; G. thoracica, which yielded the highest total VFA, merits further evaluation. Graded-dose trials and in vivo evaluation are needed to confirm its potential for mitigating ruminal methane emissions without affecting animal output.