Effect Of Forage Combination On Ruminal Fermentation And Milk Fatty Acids Composition

With improvement of economy and life, the need for health-promoting food consumption is increasing and healthy, nutritional and safe food is preferable. Manipulation of milk fatty acids composition becomes an important part of ruminal nutrition. In this study, three representative forage, alfalfa hay, rice straw and corn silage, were used to systematically investigate the in vitro gas production, rumen fermentation, associative effect and ruminal fibrolytic bacteria population in different forages combinations (Experiment 1). Meanwhile, the fatty acids composition of incubation inoculum, ruminal biohydrogenation of unsaturated C18 fatty acids and biohydrogenation associated bacteria population were analyzed (Experiment 2). The effect of different forage combinations on the production performance and milk fatty acids composition of dairy cow were also studied (Experiment 3).Experiment 1 Effect of alfalfa hay, rice straw and corn silage combinations on rumen ferementation characteristicsTwo trials were designed. In trial 1, using the reading pressure in vitro gas production technique, the combinations of alfalfa hay with rice straw at different ratios were incubated. The gas production (GP) was recored at 3,6,9,12,24,36,72 and 96 h of incubation time and GP parameters were estimated. Concentration of methane, ammonia nitrogen, microbial protein, volatile fatty acids (VFAs) and carboxymethyl cellulase of solid phase were determined at 24 h incubation. The population of Ruminococcus albus, Ruminococcus flavefaciens, Fibrobacter succinogenes and total fungi was detected using real-time PCR. The GP, GP rate, microbial protein, total VFAs and methane concentration increased with increasing level of alfalfa hay (P<0.01). The molar percentages of acetate, propionate and butyrate were not significantly affected. The carboxymethyl cellulase showed the same tendency to GP. The population of R. albus and F. succinogenes significantly increased with increasing alfalfa hay level. Increase in R. albus along with a decrease in R. flavefaciens was observed. The inclusion of alfalfa hay in mixture significantly increased the population of anaerobic fungi. In terms of both GP and microbial protein, positive associative effects were observed at all the levels of alfalfa hay, in which it was highest when alfalfa hay mixed with rice straw at 20%, probably resulted from supply of protein and pectin to rumen microbes and increase in dominating fibrolytic bacteria, F. succinogenes by alfalfa hay inclusion.In trial 2, the mixture of alfalfa hay and rice straw at 20:80 were mixed again with different levels of corn silage. Accompanied by the increase in gas production and total VFAs with increasing corn silage level, methane concentration were also significantly increased (P<0.01). The level of corn silage had little effect on acetate and butyrate molar percentage, while the propionate percentages in 0 and 25% corn silage were higher than other levels. The inclusion of corn silage in mixture significantly increased the R. albus and R. flavefaciens population, while the F. succinogenes were significantly depressed. Significant negative associative effect was observed at different corn silage level (P<0.05). The depression of F. succinogenes and total fungi might account for the negative associative effect.After analysis, it was indicated that no significant correlation between gas production and the amount of four fibrilytic bacteria, while positive correlation was found between gas production and carboxymethyl cellulase, it was suggested that the effect of forage combinations on rumen fermentation is concerned with the effect of rumen fibrolytic enzymes.Experiment 2 Effct of alfalfa hay, rice straw and corn silage combination on rumen biohydrogenation of unsaturated C18 fatty acidsThe incubation inoculum taken in Experiment 1 was used as the material. The fatty acid composition was analyzed by gas chromagraphy. The rumianl biohydrogenations of unsaturated C18 fatty acids were calculated. Meanwhile, two biohydrogenation concerned bacteria, Butyrivibrio fibrisolvens and Clostridium proteoclasticum, were analysed by real-time PCR. Compared with the other two, corn silage was riched in oleic and linoleic acid. Alfalfa hay had highest linolenic acid content, while the palmic and stearic acid in rice straw was relatively high. Inclusion of alfalfa hay significantly increased the biohydrogenation of oleic and linolenic acid (P<0.01). When alfalfa hay was at the level of 100 and 0%, biohydrogenations of the three unsaturated fatty acids were highest and lowest, respectively. When corn silage was at 50% in the mixture, the biohydrogenation of linoleic acid was higher than at other levles(P<0.01). The biohydrogenations of oleic and linolenic acid increased with increasing corn silage level. Positive correlation was observed between B. fibrisolvens and biohydrogenation of linoleic as well as C. proteoclasticum and biohydrogenation of linolenic acid. Moreover, the gas production at 24 h was postively correlated with biohydrogenation of linoleic and linolenic acids. From these results, it is indicated that the level of ferementation significantly affected the extent of unsaturated fatty acid biohydrogenation.Experiment 3 Effect of forage combination on dairy cow milk performance and milk fatty acid compositionFour diets, with different combinations of alfalfa hay, rice straw and corn silage were designed to investigated their effects on milk performance There was no significantly effect on dry matter intake, milk productionand milk fatty acid composition. The concentrate to forage ratio of all diets was at 50:50. In forage, corn silage was replaced by a mixture of alfalfa hay (60%) and rice straw (40%) at 0,25, 50, and 75%, respectively. There was no significant effect on dry matter intake, milk production, content and yield of milk fat, protein, lactose, total solid as well as solid not fat (P>0.05). With the increase of corn silage level, the stearic acid concentration in blood plasma tended to increase, but no significant difference was found between four treatments. Replacement of higher corn silage with alfalfa hay and rice straw mixture significantly decreased plasma linoleic acid and increased linolenic acid concentration (P<0.05). The effects on milk linoleic and linolenic acid were similar with that on plasma. The milk content of oleic, trans-11 oleic acid and conjugated linoleic were unaffected by treatment (P>0.05) and no significant difference was found in milk myristic, palmitic, dicosanoic and docosanoic acid concentration. In summary, the effect of alfalfa hay, rice straw and corn silage combinations on rumen fermentation may result from the effect on rumen fibrolytic bacteria. Both the fatty acid composition and rumen fermentation affected the biohydrogenation of unsaturate C18 fatty acids. Different combination of forages had no significant effect on dairy cow dry matter intake and production performance in dairy cow, while stearic, linoleic and linolenic acid concentrations were significantly changed.