|BECKETT, LINDA - Virginia Tech|
|GLEASON, CLAIRE - Virginia Tech|
|BEDFORD, ANDREA - Virginia Tech|
|LIEBE, DOUGLAS - Virginia Tech|
|YOHE, TAYLOR - Virginia Tech|
|Hall, Mary Beth|
|DANIELS, KRISTY - Virginia Tech|
|WHITE, ROBIN - Virginia Tech|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2021
Publication Date: 8/1/2021
Citation: Beckett, L., Gleason, C.B., Bedford, A., Liebe, D., Yohe, T.T., Hall, M., Daniels, K.M., White, R.R. 2021. Rumen volatile fatty acid molar proportions, rumen epithelial gene expression, and blood metabolite concentration responses to ruminally degradable starch and fiber supplies. Journal of Dairy Science. https://doi.org/10.3168/jds.2020-19622.
Interpretive Summary: Typically, animal nutrition studies measure few variables in a specific area of focus in order to understand mechanisms that can be used to predict animal responses. However, to best understand mechanisms and an animal’s likely performance, we need to understand microbial and animal responses together, not in separate studies. In this research, diets which differed in their starch and fiber degradability were offered to Holstein heifers, and the varied responses of microbial product formation, passage kinetics, and gene expression by the animal in the rumen wall were evaluated. Fiber more than starch sources altered the proportions of fermentation acids produced, the flux of those acids from the rumen, and the expression of rumen epithelium genes. Such holistic analysis of animal responses to dietary changes gives a whole-systems perspective of the impact of ruminal degradability of dietary nutrients which is also more likely to allow us to accurately predict animal responses under other scenarios.
Technical Abstract: The objective of this work was to characterize rumen volatile fatty acid (VFA) concentrations, rumen epithelial gene expression, and blood metabolite responses to diets with different starch and fiber sources. Six ruminally cannulated yearling Holstein heifers (body weight (BW); BW = 330 ± 11.3 kg) were arranged in a partially replicated Latin Square experiment with 4 treatments consisting of different starch (barley (B) or corn (C)) and fiber (timothy hay (TH) or beet pulp (BP)) sources. Treatments were arranged as a 2 x 2 factorial. Beet pulp and TH were used to create relative changes in apparent ruminal fiber disappearance while C and B were used to create relative changes in apparent ruminal starch disappearance. Each period consisted of 3 d of diet adaptation and 15 d of dietary treatment. In situ disappearance of fiber and starch were estimated from bags incubated in the rumen from d 10 to 14. From d 15 to 17, rumen fluid was collected every h from 0500 to 2300. Rumen fluid samples were pooled by animal/period and analyzed for pH and VFA concentrations. On d 18, 60 to 80 papillae biopsies were taken from the epithelium and preserved for gene expression analysis. On d 18, one blood sample per cow was collected from the coccygeal vessel. In situ ruminal starch disappearance rate (B 7.61 to 10.5 %/h vs C 7.30 to 8.72 %/h) and fiber extent of disappearance (TH 22.2 to 33.4 % of DM vs BP 34.4 to 38.7 % of DM) were affected by starch and fiber source, respectively. Analysis of VFA molar proportions showed a shift from propionate to acetate, and valerate to isovalerate on TH diets compared to BP. Corn diets favored propionate over butyrate in comparison to B diets. Corn diets also had higher molar proportions of valerate. Expression of 2 genes (heat shock protein 70 and sodium hydrogen exchanger isoform 3), were increased due to BP and 2 genes (beta-hydroxybutyrate dehydrogenase and monocarboxylate transporter 4) was increased due to TH. Plasma acetate demonstrated a tendency for a starch by fiber interaction with B-BP and C-TH diets having the highest plasma acetate. These results suggest that shifts in VFA molar proportions and epithelial transporters driven by diet changes do not necessarily convey shifts in blood metabolite concentrations.