Associative effects of wet distiller's grains, plus solubles and tannin-rich peanut skin supplementation on in vitro rumen fermentation, greenhouse gas emissions, and microbial changes

Authors: Min, Byeng Ryel; Castleberry, Bobbie - Lana; Allen, Heather; Parker, David; Waldrip, Heidi; Brauer, David; Willis, William - Will

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2019
Publication Date: 10/11/2019
Citation: Min, B., Castleberry, B., Allen, H.K., Parker, D.B., Waldrip, H., Brauer, D.K., Willis, W.M. 2019. Associative effects of wet distiller's grains, plus solubles and tannin-rich peanut skin supplementation on in vitro rumen fermentation, greenhouse gas emissions, and microbial changes. Journal of Animal Science. 97(11):4668-4681. https://doi.org/10.1093/jas/skz317.
DOI: https://doi.org/10.1093/jas/skz317

Interpretive Summary: The effect of methane on global warming is gaining attention because, as a greenhouse gas, it has a global warming potential 28 times that of carbon dioxide. There have been few studies to quantify in vitro greenhouse gas emissions associated with microbiome and rumen fermentation activities. Scientists from USDA-ARS at Bushland, TX and Ames, IA, studied how the dietary ingredients affect greenhouse gas emissions and rumen microbial activities. Our study concluded that tannin-rich peanut skin in the presence of wet distillers’ grains plus solubles suppressed methanogenesis pathways directly via anti-methanogenic activity. These data will be used to update greenhouse gas emission strategies for feedlot beef cattle and dairy cattle.

Technical Abstract: Two sets of in vitro experiments were conducted to determine effects of rumen fluid source and diets that included wet distiller’s grains plus solubles (WDGS) and tannin-rich peanut skin (PS) on the in vitro digestibility, greenhouse gas (GHG) and other gas emissions, fermentation rate, and microbial changes from collected rumen fluid. An initial study evaluated the effects of individual or equally mixed rumen liquors on in vitro ruminal gas production and GHG emissions. The second objectives involved with experiments to assess effects of various levels of PS or WDGS on the in vitro digestibility, GHG and other gas emissions, fermentation rate, and microbial changes in the rumen. All gases were collected using an ANKOM Gas Production system for methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and hydrogen sulfide (H2S) analyses. Cumulative ruminal gas production was determined using 250 mL ANKOM sampling bottles containing 50 mL of ruminal fluid (pH 5.8), 40 mL of artificial saliva (pH 6.8), and 6 g of mixed diets after a maximum of 24h of incubation. Experimental units were saturated with CO2 gas and held at 39 degrees C in a shaking incubator for 24h. Triplicate qPCR analyses were conducted to determine microbial diversity. Incubations with mixed rumen fluid in experiment 1 resulted in greater values (P < 0.01) for an in vitro gas production than incubations conducted with rumen fluid samples collected from individual steers. Results indicated that mixed rumen fluid was more appropriate for in vitro gas production studies than samples taken from individual steer. Hence, mixed rumen fluid was chosen as a source of inoculum for further experiments. When WDGS was supplied in the diet, in the absence of PS in experiment 2, cumulative CH4 production increase (P < 0.05) with 40% WDGS. In the presence of PS, production of CH4 was reduced but the reduction was less at 40% WDGS. In the presence of PS, ruminal lactate, succinate, and acetate/propionate (A/P) ratio tended to be less with a WDGS interaction (P < 0.01). In the presence of PS and with 40% WDGS, average populations of Bacteroidetes, total methanogens, Methanobrevibacter sp. AbM4, and total protozoa were less. The population of total methanogens (R2 = 0.57; P < 0.01), Firmicutes (R2= 0.46: P < 0.05), and F/B ratio (R2 = 0.46; P < 0.03) were strongly correlated with ruminal CH4 production. Therefore, there was an associative effect of tannin-rich PS and WDGS, which suppressed methanogenesis pathways directly and indirectly through modification of methanogens populations.