The Study On Rumen Fermentation,Volatile Fatty Acid Absorption Characteristics And Gene Expression In Dairy Cows Receiving Different Types Of Diets

This study was carried out to investage the effect of two different types of dietson rumen fermentation, fractional absorption rate of volatile fatty acids, ruminalpapillae morphology and expression of genes involved in VFA transporters, cellulargrowth, and VFA metabolism in ruminal papillae of dairy cows.Experiment1: An experiment was conducted to investigate responses in rumenfermentation of dairy cows receiving a corn straw or mixed forage diet. Tenprimiparous and rumen-cannulated Holstein dairy cows averaging127±13d in milk(mean±SD) were randomly assigned to CS (37.1%corn straw as sole forage) or MFdiet (3.7%Chinese wildrye+28.4%alfalfa hay+26.5%corn silage as mixed forage).The trial lasted for63d. Samples of rumen fluid were collected via cannula every6hover a72-h duration starting on day37to analyze pH, ammonia-N and VFAconcentrations. Results showed that cows fed MF diet had higher (P<0.01) ruminalacetate concentrate and ratio of acetate to propionate, and lower concentrations ofammonia-N (P<0.01), propionate (P<0.05), butyrate (P<0.01), isobutyrate (P<0.01),valerate (P<0.01) and isovalerate (P<0.01) than cows fed CS diet. Collectively, theseresults found that CS group had higher rumen ammonia nitrogen concentration whichmay suggest that CS group can not efficiently make use of nitrogen sources from diet.Experiment2: Objective of this experiment was to investigate effects of two types offorage diets on fractional absorption rate of volatile fatty acids (VFA) through therumen wall. Ten primiparous, rumen-cannulated Holstein dairy cows in late-lactationwere randomly assigned to CS (37.1%corn straw as sole roughage) or MF diet (3.7%Chinese wildrye+28.4%alfalfa hay+26.5%corn silage as mixed forage). Cowswere fed their respective diet for28d, following which n-valeric acid and Co-EDTAwere used as markers for measuring ruminal VFA absorption and passage rates.Rumen fluid was collected from ventral sac of the rumen. Results showed thatfractional rates of total VFA absorption and passage from the rumen were not affectedby dietary treatments, averaging14.78and13.64%/h, respectively. However, cows fed MF diet had higher (P<0.05) estimated clearance rate of acetate, as well as totalVFA passage rate (mol/h).Experiment3: The objective of this study was to determine the effect of differenttypes of diets on ruminal papillae morphology in dairy cows. Ten primiparous andrumen-cannulated Holstein dairy cows averaging127±13d in milk (mean±SD)were randomly assigned to CS (37.1%corn straw as sole forage and62.9%concentrate) or MF (3.7%Chinese wildrye+28.4%alfalfa hay+26.5%corn silageas mixed forage and41.4%concentrate) diet. The experiment lasted for63days. Atthe end of experiment, rumen papillae were biopsied from the ventral sac andobserved using light and transmission electron microscope. Microscopic examinationrevealed a reduction in the width of papillae (P<0.01) and the thickness of stratumcorneum (P=0.18), and an increase in the thickness of stratum granulosum (P=0.17)when cows fed MF diet. No significant differences (P>0.05) were found for thethickness of stratum spinosum and stratum basale between dietary treatments.Biopsied papillae exhibited a decline in cellular junctions and large spaces betweencells of stratum granulosum, moderate sloughing of the stratum corneum, and anaccelerated migratory state in all strata below the stratum corneum in cows fed CSdiet. These results suggest that it affects ruminal papillae morphological structurewhen cows were fed CS diet.Experiment4: This study was conducted to determine the effect of different types ofdiets on expression of18genes involved in VFA transporters, cellular growth, andVFA metabolism in ruminal papillae of dairy cows. Ten primiparous andrumen-cannulated Holstein dairy cows averaging127±13d in milk (mean±SD)were randomly assigned to CS (37.1%corn straw as sole forage and62.9%concentrate) or MF (3.7%Chinese wildrye+28.4%alfalfa hay+26.5%corn silageas mixed forage and41.4%concentrate) diet. The experiment lasted for63days. Atthe end of experiment, rumen papillae were biopsied from the ventral sac, and genesexpression was evaluated using quantitative real-time PCR. Compared with CS group, the mRNA expression of NHE-1、NHE-3、NHE-4、GPR-43and ASCC-1in ruminalpapillae was decreased in MF group (P<0.10), and the mRNA expression of MCT-1and IGFBP-5was increased in MF group (P<0.10).