TITLE:
Changing the Proportions of Grass and Grain in Feed Substrate Impacts the Efficacy of Asparagopsis taxiformis to Inhibit Methane Production in Vitro
AUTHORS:
R. D. Kinley, S. Tan, J. Turnbull, S. Askew, B. M. Roque
KEYWORDS:
Asparagopsis taxiformis, Enteric Methane, Greenhouse Gas Mitigation, Feed Substrate, Rhodes Grass, Barley Grain, In Vitro
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.12 No.12,
December
23,
2021
ABSTRACT: Benefits of the red seaweed Asparagopsis taxiformis as an ingredient
to manage methane (CH4) emissions from the red meat and dairy
industries continue to evolve. Asparagopsis has been demonstrated to
eliminate enteric CH4 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 CH4 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 CH4 production in vitro was decreased with decreasing RG/BG. Increasing the duration of fermentation
had greatest effect on CH4 at C, L, and LM levels of Asparagopsis independent of RG/BG, although magnitude of CH4 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.