| This study was conducted to investigate the effects of Aspergillus oryzae culture (AOC) and2-hydroxy-4-(methylthio) butanoic acid (HMB) on rumen fermentation with different forages as substrates and lactation performance of diary cows. In vitro gas incubation system was used to estimate the effects of AOC and HMB on gas production and rumen fermentation with substrates of Chinese wild rye (CWR), alfalfa hay (AH), corn silage (CS) and corn straw (CST). On this basis, the effects of AOC and HMB on rumen microbial populations and microbial enzyme activities were studied. The effect of AOC and HMB on the lactation performance, rumen fermentation and populations of microbes was also studied.Experiment1. Using in vitro gas production test, the effects of AOC and HMB on rumen gas production characteristics and rumen fermentation was investigated. The ratio was concentrate (corn meal) and forage (CWR, AH, CS or CST) was50:50. Each forage substrate was assigned to all6treatments in a2×3factorial arrangement with AOC (0,3or6mg) and HMB (0or15mg) as main effects. The determination of rumen fermentation was made with in vitro gas test procedure for Chinese wild rye (CWR), alfalfa hay (AH) and corn silage (CS). Gas production (GP) was recorded at2,4.8,12and24h. Ammonia-N, pH, volatile fatty acids (VFA), microbial protein (MCP) were determined at24h. The GP, potential GP and in vitro organic matter digestibility (IVOMD) significantly increased (P<0.05) when AOC and HMB was added in substrates of CWR, AH and CS substrates, and the interactive effect occurred between AOC and HMB with CS substrate (P<0.05). No effect of AOC and HMB on rumen fermentation with CST was observed (P>0.05). Adding AOC and HMB significantly increased ammonia-N concentration of CS (P<0.05). MCP concentration with substrates of CWR, AH and CS was increased with addition of AOC and HMB. And there was an interaction with MCP between AOC and HMB. Supplemental AOC and HMB increased total VFA with substrates of CWR, AH and CS except CST (P<0.01). Either AOC or HMB had little effect on molar proportions of individual VFA in CWR and AH. However, inclusion of AOC and HMB in CS substrate significantly increased molar proportion of acetate (P=0.02), and decreased proportion of butyrate (P<0.01). In addition, molar proportion of propionate increased with supplementing AOC to CS substrate (P<0.01). There was the interaction between AOC and HMB in proportion of propionate (P<0.01), butyrate (P=0.04) and ratio of acetate to propionate (A:P)(P<0.01) with CS substrate. Adding AOC and HMB had no response to the total VFA of CST, but increased molar proportion of propionate and decreased the ratio of A:P. It was inferred adding AOC and HMB could improve the rumen fermentation of substrates of CWR, AH and CS except CST and there was an interaction of CS.Experiment2. The objective of this study was to evaluate the effects of AOC and HMB on rumen microbial population using real-time PCR and enzyme activities with CWR, AH and CS on the basis of Experiment1. The effect of adding of AOC and HMB on rumen microbes was the increased fungi population for substrates of CWR and AH (P<0.01), F. succinogenes for CS (P=0.02), and S. ruminatium population for CWR and CS (P<0.01). Addition of AOC also significantly increased populations of F. succinogenes, R. flavefaciens and R. albus for CWR (P<0.01), and R. albus for AH (P<0.01). Adding HMB significantly increased populations of R. albus for CS and R. flavefaciens and S. ruminatium population for AH (P<0.01),with significant interaction with AOC (P<0.01). Besides, activities of CMCase and amylase of CWR and xylanase of AH were increased with the addition of AOC (P<0.05). Inclusion of HMB significantly increased CMCase for AH and xylanase for substrates of CWR and AH (P<0.05). There was an interaction of AOC and HMB with activities of CMCase and amylase for substrates of CWR and AH, and xylanase with CWR, AH and CS. It suggested that adding AOC and HMB could stimulate rumen fibrolytic bacteria and cellulolytic enzyme activities with substrates of CWR, AH and CS.Experiment3. The effects of adding AOC and HMB on lactation performance of dairy cows were investigated. Sixty-four multiparous Chinese Holstein cows (body weight=520kg, average days in milk=136, milk yield=31kg) were randomly allocated to4dietary treatments. A2×2factorial arrangement of treatment was adopted to provide2levels of supplemental AOC (0or5g/d per cow) and2levels of HMB (0or 25g/d per cow). HMB inclusion improved yield of milk protein and fat, percentage of milk total solid ((P<0.05)). Besides, there was a trend to increase the yield of4%FCM and the percentage of milk protein and fat (P=0.1), while addition of AOC significantly increased the percentage of milk lactose (P<0.05). Supplementation of AOC significantly decreased serum NEFA concentration and HMB significantly decreased serum lactose concentration (P<0.05). And there was a trend of HMB to increase serum Cys (P<0.1). It was included addition of AOC significantly decreased blood NEFA concentration, adding HMB increased the percentage of milk protein and fat, lactose and TS and the yield of milk protein and fat of Chinese Holstein cows in mid-lactation.Experiment4. The effects of AOC and HMB on rumen fermentation and microbial populations of dairy cows were investigated. The experiment design was the same with Experiment3. Six cows of each treatment were chosen to collect ruminal liquid by an oral stomach tube in the middle and late period of the experiment. Supplementation of AOC and HMB significantly increased concentrations of rumen microbial protein and total volatile fatty acids. Adding HMB significantly increased molar proportion of acetate, but decreased molar proportion of propionate so increased the acetate to propionate ratio. Populations of rumen fungi, F. succinogenes and R. flavefaciens relative total bacteruak16S rDNA were increased with supplementing AOC and HBM. Activity of carboxymethl cellulase (CMCase) was significantly higher by adding AOC and HMB and there was an interaction between AOC and HMB. From this study, it is inferred supplementation of AOC and HMB improved rumen fermentation and lactation performance.by stimulating rumen microbes and CMCase activity.In summary, the effects of AOC and HMB on different forages were different. Inclusion of AOC and HMB significantly improved rumen fermentation of CWR, AH and CS, while had no effect on CST. It was indicated that the effect of AOC and HMB on rumen fermentation was concerned with the effect of rumen fibrolytic bacteria population and rumen CMCase activity. Addition of AOC and HMB to the diets of Chinese Holstein dairy cows in mid-lactation had no effect on DMI and milk yield. However, adding AOC significantly decreased plasma NEFA concentration by stimulating rumen total VFA and improved energy metabolism in dairy cows. Adding HMB significantly increased concentrate and yield of milk protein and fat and yield of4%FCM by stimulating total VFA, acetate proportion and MCP. It was inferred the effect of AOC and HMB on dairy cows probably resulted from the stimulation of fungi, fibrolytic bacteria and CMCase activity. |
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