| A relevant metabolic disorder in ruminants is acidosis. Many reports estimated that this disease was related to the disorder of the rumen microbial composition when more rumen fermentable carbohydrate was used. Under the inormal rumen fermentation conditions, the VFA and lactic acid production was improved dramatically, and some unhealthy metabolites such as LPS and histamine concentration were improved. However, which caused the improvement of the lactate concentration? Is there some relationship between the microbial compostion and the VFA production? What is the correct correlationship the LPS concentration, rumen microbial compostion and the diet? To our knowledge, there is fewer report on it. To investigate the major producer of the lactate and explore the relationship between LPS concentration and the microbial comostion, this present study was conducted using the classic microbial techniques combined with PCR/DGGE, Realtime PCR and other molecular methods. This thesis was described in the following three sections.In the first section, the study was conducted to isolate the isolate lactic acid bacteria and investigate its characteristics and the potential role in the rumen of goat. Six lactic acid producing bacteria were isolated from the rumen contents of two goats fed a diet mixed with the corn and the grass. The results showed that two isolates were identified as Streptococcus bovis, and the others were identified as Weissella sp. The isolates extended the logarithmic growth phase from2h to8h after inoculation. The concentration of L-lactate production was beyond14mmol/L in fermentation supernatants when isolates of L3, L5, L8, L10and L12was used as inoculants, whereas L2isolate produced only1.7mmol/L of L-lactate. The isolates of L3, L5, L2, L10and L8isolate produced14mmol/L,4.17mmol/L,5.07mmol/L and0.83mmol/L D-lactate, respectively. The results indicated the Streptococcus bovis and the Weissella sp. was the predominant lactate producer in the rumen of the goat, and all isolates can produce both the D-and L-lactate. In the second section, the changes of the ruminal fermentation, the LPS concert ration in rumen liquid and blood and the ruminal microbial composition were investigated as the diet changed from the whole forage to the mixed diet. Four local sheep were gelded and designed for a self-controlled trial. The trail consisted of three periods corresponding to three diets (whole forage, medium-forage diet (F:C=5:5, DM basis), low-forage diet (F:C=2:8, DM basis). The results showed that, as the proportion of concentrate versus forage in the diet increased, the pH value decreased (P<0.05), and the acetate, propionate, butyrate, isobutyric acid, valerate, isovalerate and TVFA production groups were improved (P<0.05), the ration of the acetate to propionate was reduced (P<0.05). Lactate was not detected in the whole forage group. The LPS concert ration in blood and rumen liquid increased (P<0.05). No significant differences were observed on the viable counts of lactobacillus and E.coli among the three diet. The analysis of the DGGE profiles of the bacillus showed that there were some new bands appeared when the diet changes from the whole forage to the F:C(4:6) and F:C(8:2) diet. The Real-time PCR results showed the copies of the16SrRNA of lactobacillus and total bacteria affected by the high proportion of the concentration, whereas no significant changes were found on the number of E.coli and the Streptococcus bovis. The results indicated that the proportion of dietary concentrates affects ruminal fermentation and the composition of the rumial microbial.In the last section, the effects of acarbose addition on in vitro rumen fermentation characterizes of ruminal bacteria was studied using the batch culture techniques. The diets consisted of the0.8g grinding corn and0.2g grinding chinless.The acarbose was added to achieve final acarbose concentrations of4mg,8mg andl6mg in treatment. Control bottles had the same ingredients except no acarbose. Both acarbose treatment and the control had four replicate bottles. The results showed that during24h incubations, acarbose addition increased the pH and the NH3-N concentration, and decreased the ratio of the acetate to propionate, isobutyrate, valerate, lactate, acetate, propionate, butyrate and TVFA production(P<0.01). There is no significant difference of isovalerate between the control and the treatment (P=0.794). The determination of the kinetic parameters of the in vitro fermentation shows that acarbose addition decreased the rate of gas production during the first24h of fermentation. The results suggested that acarbose addition can decrease the fermentation activity effectively and has the potential to prevent the rumen acidosis. |
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