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 changes1

Two sets of in vitro rumen fermentation experiments were conducted to determine effects of 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. The objectives were to assess associative 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 24 h of incubation. Fermenters were flushed with CO2 gas and held at 39 °C in a shaking incubator for 24 h. Triplicate quantitative real-time polymerase chain reaction (qPCR) analyses were conducted to determine microbial diversity. When WDGS was supplied in the diet, in the absence of PS, cumulative CH4 production increased (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 Firmicutes/Bacteroidetes (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 both directly and indirectly by modifying populations of ruminal methanogens.

Effect of Corn Processing and Wet Distiller’s Grains with Solubles on Odorous Volatile Organic Compound Emissions from Urine and Feces of Beef Cattle

Wet distiller’s grains with solubles (WDGS) are a common feed ingredient in beef feedlot diets but the high nitrogen content of these diets creates air quality issues, primarily due to the aromatic compounds emitted during protein fermentation. Use of high moisture corn (HMC) instead of dry-rolled corn (DRC) in cattle feedlot diets has been shown to reduce some odors associated with excess starch in cattle feedlot diets. We hypothesized that using HMC in place of DRC in diets containing WDGS would reduce some of the odors associated with WDGS-DRC diets. A 4 × 4 replicated Latin square with a 2 × 2 factorial arrangement of treatments was used. Diets contained either DRC or a 2:1 ratio of HMC and DRC, with WDGS at either 25% or 45% of the diet dry matter resulting in four treatments: DRC-25, HMC-25, DRC-45 and HMC-45. Odorous compounds were measured from feces and urine of cattle fed the four diets. Feces from cattle fed diets containing 45% WDGS had a higher flux of p-cresol (9.42 µg m-3 min-1), 4-ethyphenol (0.04 µg m-3 min-1), and total aromatic compounds (13.56 µg m-3 min-1) compared to feces from cattle fed 25% WDGS (3.38, 0.03, and 6.86 µg m-3 min-1, respectively). Corn processing did not influence fecal odor flux. Urinary flux of odorous compounds was largely unaffected by corn processing method and only p-cresol (9.58 µg m-3 min-1), and total aromatic compounds (11.34 µg m-3 min-1) were higher for cattle fed 45% WDGS compared to cattle fed 25% WDGS (7.65 and 9.12 µg m-3 min-1, respectively for p-cresol and total aromatics). Overall there were no significant differences in odor potential, as determined by odor activity value (OAV), for cattle fed diets containing HMC and DRC with either concentration of WDGS. From these results, we interpret that producers may feed diets containing HMC or DRC in combination with WDGS at inclusion rates up to 45% with only minimal impacts of air quality. Keywords: Beef cattle manure, Distiller’s dried grain solubles, Dry-rolled corn, High-moisture corn, Odor, Volatile organic compounds.