Effects of unprotected choline chloride on microbial fermentation in a dual-flow continuous culture depend on dietary neutral detergent fiber concentration

Abstract

Choline is usually supplemented as ruminally protected choline chloride to prevent its degradation in the rumen, but the effects of unprotected choline on ruminal fermentation are unclear. Some research indicates a possible role of dietary fiber on microbial degradation of choline; therefore we aimed to evaluate the effects of unprotected choline chloride on ruminal fermentation and to investigate whether those effects depend on dietary neutral detergent fiber (NDF) concentration. Our hypothesis was that dietary NDF concentration would influence choline chloride effects on microbial ruminal fermentation. We used 8 fermentors in a duplicated 4 × 4 Latin square with a 2 × 2 factorial arrangement, combining 2 factors: (1) dietary NDF concentration and (2) unprotected choline chloride supplementation. Resulting treatments are (1) 30%NDF/Ctrl [30% NDF control diet without supplemental choline (Cho)]; (2) 30%NDF/Cho [30% NDF diet plus 1.9 g of choline ion per kg of dry matter (DM)]; (3) 40%NDF/Ctrl (40% NDF control diet without supplemental choline); and (4) 40%NDF/Cho (40% NDF diet plus 1.9 g of choline ion per kg of DM). Four 10-d periods were completed, each consisting of 7 d for adaptation and 3 d for collection of samples for estimation of nutrient disappearance and daily average concentrations of volatile fatty acids and NH 3 -N. In addition, kinetics of pH, acetate, and propionate were evaluated at 0, 1, 2, 4, 6, and 8 h after morning feeding. On the last day of each period, bacteria pellets were harvested for 15 N analysis and N metabolism. Fixed effects of dietary NDF concentration, unprotected choline chloride supplementation, and their interaction (NDF × Cho) were tested using the MIXED procedure of SAS version 9.4 (SAS Insti-tute Inc., Cary, NC). Choline tended to increase total volatile fatty acid concentrations and decreased acetate molar proportion regardless of dietary NDF concentration, but it increased propionate molar proportion and decreased acetate to propionate ratio only with the 30% NDF diet. Supplementing choline decreased NDF disappearance regardless of dietary NDF; however, organic matter disappearance tended to be reduced only when choline was added to 40% NDF. Our data indicate that unprotected choline chloride effects on ruminal fermentation depend on dietary NDF concentration, allowing for a greater propionate synthesis without decreasing organic matter disappearance when fed with a 30% NDF diet.

Effects of choline chloride on the ruminal microbiome at 2 dietary neutral detergent fiber concentrations in continuous culture

“…Procedures for care and handling of animals required for this experiment were approved by the Institutional Animal Care and Use Committee at the University of Florida. Details on the experimental design and diets can be found in our companion study (Arce-Cordero et al, 2021). Briefly, 8 fermentors of a dual-flow continuous culture system were used in a duplicated 4 × 4 Latin square design.…”

“…The amount of supplemental choline is based on our companion study indicating greater propionate molar proportion and lower NDF digestibility in continuousculture fermentors (Arce-Cordero et al, 2021) and it had been previously defined based on scientific literature. Because our goal was to determine the effects of unprotected choline on ruminal fermentation and microbiome, only literature in which unprotected choline was supplemented to ruminants was considered to determine our experimental dose.…”

“…At the end of each day (24 h) of fermentation, total liquid and solid digesta effluents of the same fermentor were weighed, combined, and samples were collected and stored at −20°C for further analyses of propionate as detailed in Arce-Cordero et al (2021). Briefly, 10 mL of sample was strained through 4 layers of cheese- cloth, acidified with 100 µL of 50% H 2 SO 4 , and stored at −20°C for subsequent analysis.…”

“…Similarly, greater relative abundance of Firmicutes and lower relative abundance of Bacteroidetes result from a reduction in dietary NDF concentration (Plaizier et al, 2017), which may therefore influence ruminal degradation of choline. Recently, Arce-Cordero et al (2021) reported greater molar proportion of propionate and lower NDF digestibility in continuous culture when unprotected choline chloride was supplemented with 30% NDF diets; such effects were not observed with 40% NDF diets, indicating that utilization of choline by ruminal microorganisms is dependent on dietary NDF and may have an effect on propionate-synthesizing bacteria in the rumen. To our knowledge, the effects of unprotected choline on ruminal bacterial populations and their possible association with the type of diet have not been published.…”

“…Our objective was to evaluate the effects of unprotected choline chloride on the ruminal microbiome at 2 dietary NDF concentrations. Based on our previous results (Arce-Cordero et al, 2021), we hypothesized that unprotected choline chloride would differentially affect ruminal bacterial populations depending on dietary NDF concentration.…”