PSXIV-17 Red seaweed Gracilaria spp. can mitigate enteric methane emissions in beef cattle.

Abstract Enteric methane (CH4) in ruminants might lead to losses of dietary gross energy, reducing production efficiency. Red seaweed contains bromoform, a chemical known for decreasing enteric CH4 emissions in ruminants. This study evaluated the effects of different inclusion levels (0, 1, 5, and 10%) of red seaweed Gracilaria spp. on in vitro fermentation parameters using ruminal fluid from two cannulated animals. Experiment 1 utilized a randomized complete block design (RCBD) with three replicates. Fixed effects were algae, inclusion level, and drying method, with incubation day as a random effect. Experiment 2 employed a RCBD with fixed effects of algae and inclusion level, and incubation day as a random effect. Polynomial contrasts (linear, quadratic, and cubic) were applied in both experiments. In experiment 1, G. mammillaris (GM) and G. damicornis (GD) were evaluated under two drying methods, sundried (SD) and freeze dried (FD). For pH, a positive linear effect was observed (P < 0.01) for GMSD, GDSD, and GDFD, and a quadratic effect (P < 0.03) for GMFD. A negative linear effect of algae inclusion was observed (P = 0.05) in GMFD and GDSD for CH4/g of dry matter (DM) incubated, and in GDSD for total volatile fatty acids (mM; P = 0.04). An interaction between algae spp. and drying method was observed for acetate molar proportions (MP; P = 0.04), with a linear increase for GMFD and GDSD (P = 0.01 and P = 0.04 respectively). Propionate MP decreased linearly for GMFD (P = 0.01) and the acetate to propionate ratio was higher for GMSD (P = 0.04) and GMFD (P < 0.01). Experiment 2 evaluated three Gracilaria spp.: G. mammillaris (GM), G. damicornis (GD), and G. coronopifolia (GC). Algae were snap-frozen with liquid nitrogen and subsequently freeze dried, prior to incubation. A negative linear effect in algae inclusion level was observed in total gas produced for GD (P = 0.03) and GC (P = 0.05). A linear decrease was observed in CH4/g of DM incubated for GD (P = 0.01) and GC (P = 0.01). This decrease persisted for CH4/g of OM fermented (P = 0.05) in both GD and GC. Acetate MP increased linearly with algae inclusion level for GD (P = 0.03), whereas propionate MP linearly decreased in GC (P = 0.03), and a cubic effect was observed for GD (P = 0.04). Inclusion of the Gracilaria spp. has the potential to reduce CH4 production; however, this reduction was not correlated with algae bromoform concentrations. Other compounds might have affected the fermentation, and they warrant further investigation. Snap freezing resulted in greater bromoform concentration regardless of drying method, indicating that harvesting method is an important aspect to manage during red algae production for CH4 mitigation.