337. Ex Vivo Fermentation of Hempseed by Cattle Rumen Microbes and Transformation of Cell Wall Carbohydrates.

Abstract Since the 2018 Farm Bill, US growers have been allowed to cultivate hemp (Cannabis sativa L.), prompting interest in exploring the use of hemp products in ruminant diets. Hempseed has an unusual cell wall polysaccharide profile compared to other common oilseeds and grains. The carbohydrate structure of hemicellulose polysaccharides affects the interaction between cellulose and hemicellulose and may influence the rate of microbial fermentation. To better understand the utilization of hempseed fiber by ruminal microbiota, an ex vivo study was performed. Rumen fluid was obtained from corn- and soybean-fed cattle (n = 3). Incubation of water-insoluble hempseed cell wall material with rumen fluid in an ANKOM Daisy II system yielded an in vitro true digestibility (IVTD) of 36.02 ± 2.91% after 48 hours. Changes in the linkage types of the cell wall polysaccharides during fermentation were determined by the generation and analysis of partially methylated alditol acetates (PMAAs) with GC-MS and GC-FID. Changes in the monosaccharide composition of the hempseed carbohydrates were assessed by determining the monosaccharide composition via HPAEC-PAD following acidic hydrolysis. All analyses were completed in triplicate. Statistical analyses were performed with OriginPro 2017 software using a one-way analysis of variance (ANOVA) followed by Tukey’s means comparison tests. Statistical significance was assigned for p-values ≤0.05. The linkage type corresponding to linear xylans was abundant in hempseed fiber and was significantly concentrated in the residues remaining after 48 hours of fermentation compared to the starting material, which indicates that this polysaccharide structure contributes to hempseed fiber’s resistance to degradation by ruminal microbes.