Effects Of Partially Replacing Starch In A High Concentrate Diet With Soluble Sugar On Rumen Fermentation And Trans-10 Biohydrogenation Pathway In Vitro

The positive influence of replacing dietary starch with sugars on milk fat production was believed to partially attribute to the inhibition of the rumen trans-10 biohydrogenation pathway. Such inhibition might be relatedmainly to the alterations in rumen pH, rumen microorganisms or metabolites that were caused by the particular fermentation patterns of sugars. However, the effects of sugar addition on rumen fermentation have been considerably variable, and direct investigation of sugar on rumen biohydrogenation of fatty acid is limited, more informatios are needed to certify the inhibition of sugar on rumen trans-10 biohydragenation pathway. To lay a foundation for the future in vivo study and supply evidence for the utilization of sugars in dairy production, a preliminary experiment was firstly carried out firstly to determine whether there was an inhibition effect by replacing dietary starch with sugar, cornstarch in a high concentrate basal diet(forage to concentrate ratio = 40:60) was replaced by 0(control), 3%, 6% and 9% of sucrose using an in vitro batch incubation system. Then a second experiment using a 3×4 factorial design was carried out to determine the effects of replacing cornstarch in the same basal diet with 0(control), 3%, 6% and 9% of sucrose, fructose and lactose on rumen fermentation pattern and fatty acid biohydrationation. The following results were obtained:1. Treatments did not affect ruminal pHexcept the 9% sucrose treatment(P <0.05). Replacing dietary cornstarch with sugar had no influence on concentrations of total VFA(P >0.05),but the profiles of the individual VFA changed in comparison with the control group(P <0.05), the influence of 9% sucrose on p H remains to be confirmed. Because 9% sucrose decreased ruminal pH in comparison with the control treatment(P <0.05), which was different from the result in first experiment.2. The consistent results were that sugar inclusion in the dietproduced more molar proportion of butyrate or less acetate, isobutyrate and isovalerate in comparison with the control treatment(P <0.05). However, the yield ofpropionate was various in different sugar groups.Replacing corn starch with 9% fructose increased the molar proportion of propionate(P< 0.05), but the 9% lactose decreased the molar proportion of propionate compared with the control treatment(P <0.05). Treatments did not affect the concentrations of NH3-N except the 9% sucrose treatment(P <0.05), which decreased concentrations of NH3-N in comparison withthe control group(P <0.05).3. Replacing starch in a high-concentrate diet with sugar significantly affected the metabolism of ruminal fatty acids, but different sugarshad various effects(P < 0.05). The 6% and 9% sucrose groups inhibited the rumen trans-10 biohydrogenation pathway by decreasing concentrations of CLAtrans-10, cis-12 or C18:1trans-10(P < 0.05)and by increasingthe ratio of trans-11 to trans-10(P <0.05). The 3% and 9% lactosegroups decreased concentrations ofC18:1trans-10 but had no effect on other fatty acidsinthe rumen trans-10 biohydrogenation pathway(P > 0.05). There were no influence on the rumen trans-10 biohydrogenation pathway for fructose groups(P > 0.05). In addition, biohydrogenation of C18:2 n-6 and C18:3 n-3 decreased in all sugar groups(P < 0.05).4. Replacing dietary cornstarch with sugarinfluenced the abundance of bacteria related to the rumen trans-10 biohydrogenation pathway(P < 0.05). Compared with the control group, the 6% and 9% sucrose groups increased the number ofB. fibrisolvensand B. fibrisolvens+ Pseudobutyrivibrio spp.which were well known as trans-11 producerafter 6 h in vitro incubation(P <0.05). The 6% and 9% fructose groups increased the populations of B.hungatei after 24 h in vitro incubation(P <0.05),and the3% and 9% lactose groups increased the number of B.fibrisolvens+ Pseudobutyrivibrio spp. after 24 h in vitro incubation(P <0.05). Furthermore, the abundance of M. elsdeniiin all types of sugar groups was less than the control group. The 3% and 9% of both fructose and lactose groups decreased the number ofS. bovis(P <0.05).After incubation for 6 h, the effect of sucrose on the number of the ruminal bacteria could be investigated, while for lactose and fructose groups under the same culture conditions, the effect could be investigated after 24 h.5. Different sugars, levels and their interaction had different effects on rumen fermentation and rumen trans-10 biohydrogenation pathway(P < 0.05). Overall, sucrosehad greater inhibition effect on rumen trans-10 pathway and changed more rumen bacterial species in comparison with lactose and fructose. Lactose had greater ability to produce more molar proportion of butyrate, but it had little effect on other index. The effect degree of fructose was between that of sucrose and lactose.The above results indicated that replacing cornstarch in a high-concentrate diet with sugar in vitro did not alter rumen pH, but increased molar proportions of butyrate. Sugar inclusion in the diet inhibited the rumen trans-10 biohydrogenation pathway. The increase of butyrate production in sugar fermentation and the inhibition of rumen trans-10 biohydrogenation pathway were partially due to increasing the abundance of bacteria well known as trans-11 producerand decreasing the abundance of bacteria well known as trans-10 producer. Different sugars had different effects on rumen fermentation and rumen trans-10 biohydrogenation pathway. Overall, the inhibition effect on rumen trans-10 pathway was greater when starch was replaced by sucrose in comparison to lactose and fructose, especially in the 6% and 9% levels.