Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2023
Publication Date: 3/17/2023
Citation: Andreen, D.M., Billman, E.D., Brito, A.F., Soder, K.J. 2023. Effect of incremental amounts of Asparagopsis taxiformis on ruminal fermentation and methane production in continuous culture with orchardgrass herbage. Animal Feed Science and Technology. 299:115641. https://doi.org/10.1016/j.anifeedsci.2023.115641.
Interpretive Summary: While red seaweed has been shown to reduce enteric methane in ruminant livestock by >95% in preliminary studies, it is not known what effect seaweed has on overall ruminal fermentation and nutrient digestibility. We supplemented a pasture-based diet with three levels of red seaweed to evaluate effects on ruminal fermentation and methane production in a continuous culture fermentor system. We found that methane production was almost completely suppressed at all levels of seaweed supplementation compared to the pasture-only diet (no seaweed). However, seaweed also reduced ruminal fermentation, which may impair growth or milk production in grazing ruminants. Further research is needed to identify an optimal dose of seaweed to maintain animal production and to address issues such as cost and scale of production.
Technical Abstract: Enteric methane (CH4) emission from ruminants is a significant contributor to total greenhouse gas emissions from the livestock sector. Previous research has demonstrated that the red seaweed Asparagopsis taxiformis (AT) strongly inhibits ruminal methanogenesis in batch culture and in vivo experiments, but its effects on CH4 production have not been assessed in continuous culture or with pasture-based diets. A 4-unit continuous culture fermentor system fed orchardgrass (Dactylis glomerata L.) and incremental amounts of AT (0, 0.5, 1, or 1.5%; diet dry matter (DM) basis) was used to assess nutrient digestibility, volatile fatty acid (VFA) concentration, CH4 output, and N metabolism. Treatments were randomly assigned to fermentors in a 4 × 4 Latin square design with 7 d of treatment adaptation and 3 d of sample collection. Fermentors were fed a total of 76 g of DM per day, split equally into 4 feedings (730, 1030, 1400, and 1900 h). In each of the final 3 d of each experimental period, samples of total effluent were taken for analysis of ammonia N and VFA, and 1 L of effluent was collected for a composite. At the end of the period, composited effluent was blended and then lyophilized for analysis of DM, ash, neutral and acid detergent fiber, crude protein, and total purines. Headspace CH4 concentration in each fermentor was measured every 15 min (192 readings/d) using an FTIR gas analyzer, and pH was recorded every 2 min. Data were analyzed using the MIXED procedure of SAS with orthogonal polynomial contrasts. Methane production in fermentors was reduced by 99.9% within the first 24 h of each experimental period and remained predominantly below the limits of detection for the remaining 9 d. Apparent digestibility of neutral and acid detergent fiber, as well as apparent and true DM digestibilities, were linearly decreased by AT inclusion. Total VFA concentration and molar proportion of acetate decreased in a cubic pattern, and molar proportions of propionate and valerate increased cubically. Ammonia N concentration decreased cubically, while bacterial efficiency increased linearly in response to incremental doses of AT. A. taxiformis acutely and rapidly inhibited CH4 production from of orchardgrass in continuous culture, but also negatively affected nutrient digestibility and VFA production. Further research is required to determine optimal dietary level of AT to mitigate CH4 production while avoiding negative impacts on ruminal fermentation.