Changing the Proportions of Grass and Grain in Feed Substrate Impacts the Efficacy of <i>Asparagopsis taxiformis</i> to Inhibit Methane Production <i>in Vitro</i>

Abstract

Benefits of the red seaweed Asparagopsis taxiformis as an ingredient to manage methane (CH 4 ) emissions from the red meat and dairy industries continue to evolve. Asparagopsis has been demonstrated to eliminate enteric CH 4 emissions in vitro and reduce it greater than 80% in animals. Variability in animal studies is suspected to be associated with variable inclusion and proportions of grass and grain in the diet. This in vitro study aimed to elucidate effects of gradient grass to grain proportions in the fermentation using five steps from 100% Rhodes grass (RG) to 100% barley grain (BG). Gradient inclusion of Asparagopsis was in six steps of Control with no inclusion (C), Low (L), Low-Medium (LM), Medium (M), Medium-High (MH), and High (H) levels tested in three fermentation durations (24 h, 48 h, 72 h). There was significant effect of RG/BG and inclusion of Asparagopsis such that CH 4 production decreased with increasing Asparagopsis independent of RG/BG; however, there was enhanced reduction at greater proportions of BG. Thus, the level of Asparagopsis required to completely inhibit CH 4 production in vitro was decreased with decreasing RG/BG. Increasing the duration of fermentation had greatest effect on CH 4 at C, L, and LM levels of Asparagopsis independent of RG/BG, although magnitude of CH 4 production was greater for higher proportions of BG for the C and L levels. Digestibility of in vitro substrate increased with fermentation duration and increasing BG; however, there was no change associated with inclusion levels of Asparagopsis . Increases in total volatile fatty acids (tVFA) were observed with increased fermentation duration and concomitant with increasing substrate digestion. Increasing proportions of BG induced increase in tVFA. In contrast, and independent of changes in substrate, increasing inclusion of Asparagopsis had little effect on tVFA. The acetic and propionic acid ratio (AA:PA) decreased with decreasing RG/BG and increasing Asparagopsis . This pattern was most pronounced with 100% BG and MH-H Asparagopsis levels. Compared to control, there was decrease in the AA:PA ratio with addition of even L levels of Asparagopsis and with L compared to LM inclusion levels. Increasing levels of BG and Asparagopsis resulted in significant decreases in AA:PA ratios and CH4 production. This study has confirmed that gradient levels (ratio) of grass and grain in a feed mix impact the antimethanogenic efficacy of Asparagopsis during in vitro fermentation with rumen fluid.