Whole stillage inclusion level influences in vitro fiber digestibility and ruminal fermentation of tall fescue hay

Authors: AJAYI, HAPPINESS - Kentucky State University; Davis, Brittany; LEHMKUHLER, JEFFREY - University Of Kentucky; HARMON, DAVID - University Of Kentucky; JIANG, YUN - Kentucky State University; TROTTA, RONALD - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2025
Publication Date: 1/17/2025
Citation: Ajayi, H.J., Davis, B.E., Lehmkuhler, J.W., Harmon, D.L., Jiang, Y., Trotta, R.J. 2025. Whole stillage inclusion level influences in vitro fiber digestibility and ruminal fermentation of tall fescue hay. Journal of Animal Science. 103. Article skaf006. https://doi.org/10.1093/jas/skaf006.
DOI: https://doi.org/10.1093/jas/skaf006

Interpretive Summary: Whole stillage, a byproduct of ethanol production, is frequently available to beef producers as a potential low-cost feed supplement. The acidic pH of whole stillage is a concern for supplementing high-forage diets and its effects on fiber digestibility and ruminal fermentation are not well characterized. In the current study, increasing whole stillage inclusion (0%, 9.06%, 18.1%, 36.3% inclusion in an in vitro ruminal inoculum ) was evaluated in a high-forage diet using an in vitro model to simulate fermentation occurring in the rumen. Increasing whole stillage inclusion decreased in vitro ruminal dry matter and fiber digestion of tall fescue hay. Possible factors contributing to decreased fiber digestion with whole stillage inclusion include the high lipid content, decreased final pH in the in vitro ruminal media, decreased cellulolytic bacteria concentration, and decreased concentrations of branched-chain volatile fatty acids. These results are interpreted to suggest that high levels of dietary whole stillage inclusion could potentially have negative associative effects on the digestion and fermentation of high-forage diets. More research is needed to determine optimal feeding strategies for supplementing liquid distillery byproducts as low-cost alternative feed sources for ruminants.

Technical Abstract: With the growing bourbon industry in the Southeastern U.S. leading to increased production of distillery by-products, there is a pressing need to explore sustainable uses for whole stillage as a potential feed ingredient for ruminants consuming high-forage diets. The acidic nature and high moisture content of whole stillage raise concerns regarding its impact on ruminal fermentation and fiber digestibility. The objective of this study is to evaluate the effects of whole stillage inclusion on the in vitro fiber digestibility and ruminal fermentation of tall fescue hay. Ruminal contents were obtained from two ruminally-cannulated Angus × Holstein steers (390 ± 4.49 kg BW) fed a basal diet consisting of 90% tall fescue hay and 10% cracked corn. Whole stillage was obtained from a local distillery and homogenized. Whole stillage replaced water in the Goering and Van Soest buffer preparation at 0.00%, 9.06%, 18.1%, or 36.3% on a v/v basis to simulate ruminal fill of whole stillage under practical conditions. Tall fescue hay was used as the substrate and added in F57 filter bags. The inoculum was sparged with CO2 to maintain anaerobic conditions and incubated at 39°C for 48 hours. Gas production was continuously measured during the 48h incubation, and the headspace gas and fermentation media were collected post-incubation for the analysis of methane, pH, microbial biomass, dry matter (DM) disappearance, neutral detergent fiber (NDF) digestibility, volatile fatty acid (VFA) concentrations, and ammonia concentration. Results were analyzed using the GLM procedure of SAS using polynomial contrast statements for statistical comparison. Whole stillage inclusion linearly decreased (P = 0.002) apparent DM digestibility. A quadratic effect (P = 0.03) was observed on true DM and NDF disappearance of tall fescue hay, with both values declining as whole stillage inclusion levels increased. The rate and extent of gas production, methane production, and total VFA concentration increased (P < 0.05) with increasing whole stillage inclusion. The final pH of the fermentation media linearly decreased (P < 0.001) with increasing levels of whole stillage inclusion. The molar acetate, valerate, isovalerate, and isobutyrate proportions decreased (P < 0.05) with increasing whole stillage levels. The molar propionate proportion responded quadratically (P < 0.01), with the peak proportion occurring at 36.3% whole stillage inclusion. Increasing whole stillage inclusion linearly decreased (P < 0.001) the viable number of cellulolytic and 2-deoxyglucose-resistant cellulolytic bacteria in the fermentation media. Peptide- and amino acid-utilizing bacteria increased linearly (P < 0.001) and hyper-ammonia-producing bacterial concentration peaked (quadratic: P = 0.05) at 36.3% whole stillage inclusion. Increasing whole stillage inclusion in the in vitro ruminal media demonstrated negative associative effects on the fermentation of tall fescue hay, as indicated by decreased NDF disappearance, cellulolytic bacteria, pH, and branched-chain VFA proportions.