ABSTRACT
Linamarin-eugenol and its combination as food additive on methanogenic bacteria, fermentation parameters and methane production in vitro

Carmen Zavaleta-Cordova1*, Jorge ?vila-Stagno2, Nelson Vera-Aguilera3, Edgar Enrique Sosa-Rubio1, Ver?nica Barra-Valdebenito3, Daniela Jim?nez-Arriagada3, and V?ctor Hugo Parraguez-Gamboa3
 
Secondary plant metabolites (SPMs) can influence the reduction of enteric methane (CH4) emissions in ruminants. This study aimed to evaluate the effects of supplementing diet with cyanogenic glucoside linamarin (LIN), essential oil eugenol (EU), and their combination (LIN+EU) on methanogenic microorganisms, CH4 production, and rumen fermentation parameters in vitro. The basal diet (BD) (alfalfa [Medicago sativa L.] hay and oat [Avena sativa L.] grain in a 3:1 ratio) was supplemented with LIN, EU, and LIN+EU mixtures and placed in amber bottles. The experimental treatments were: T1, BD (control); T2, BD-LIN (20 mg L-1); T3, BD-LIN (40 mg L-1); T4, BD-EU (400 mg L-1); T5, BD-LIN+EU (20 mg L-1+ 400 mg L-1); and T6, BD-LIN+EU (40 mg L-1+ 400 mg L-1). The treatments were inoculated with rumen fluid and incubated for 6, 12, and 24 h to assess abundance of total bacteria (TB), methanogenic archaea, and ruminal fermentation parameters. The CH4 production was significantly reduced (p < 0.001) with inclusion of LIN, EU, and LIN+EU, particularly at 12 and 24 h incubation. However, at these same time points, in vitro DM disappearance (IVDMD) was also reduced (p < 0.001), except when LIN was included alone, highlighting its advantage in this variable. Rumen pH remained relatively stable at 6 and 12 h but decreased (p < 0.001) at 24 h with LIN. The pH values ranged between 6.65 (minimum) and 6.85 (maximum), which are optimal for microbial activity. Total bacterial abundance (TB) was not affected (p > 0.05) by treatments, but methanogenic archaea abundance was significantly reduced (p < 0.001) at 24 h with the LIN+EU mixtures (T5 and T6), coinciding with the highest CH4 reductions of 36.9% and 56.7%, respectively. At 24 h, IVDMD with LIN alone was 51.83%, whereas EU alone resulted in 46.48%. In conclusion, LIN+EU mixtures T5 and T6 had a synergistic effect, effectively reducing CH4 emissions, demonstrating the combined impact of different SPMs mechanisms of action.
Keywords: Archaea, methanogenesis, mitigation, ruminal metabolism, secondary metabolites.
1Instituto Nacional de Investigaciones Forestales, Agr?colas y Pecuarias (INIFAP), CE-Chetumal-Centro de Investigaci?n Regional del Sureste (CIRSE), Quintana Roo, M?xico.
2Universidad de Concepci?n, Facultad de Ciencias Veterinarias, Chill?n, Chile.
3Universidad de Chile, Facultad de Ciencias Veterinarias y Pecuarias, Santiago, Chile.
*Corresponding author (zavaleta.maria@inifap.gob.mx).