| This study was designed to investigate the effect of active dried yeast (viable bacteria counts≥2×1010) on ruminal fermentation in vitro, degradation of roughages, biochemical indexes of blood and microbial community. This thesis contains three parts:the effects of different concentrations of active dried yeast on rumen fermentation in vitro was studied in experiment 1. The optimal dietary supplementation of yeast was selected. Experiment 2,3 was conducted to determine effects of appropriate amounts of active dried yeast on ruminal digestibility of different roughages, biochemical indexes of blood and microbial community of beef cattle, respectively. The main results are as follows:In Exp.1, an in vitro test was used to determine the effects of various level (0%, 0.05%,0.075%,0.1%,0.125%, and 0.15%) of active dried yeast on rumen fermentation of total mixed ration with artificial rumen device. Gas production was recorded and fermentation liquor was collected at 2、4、8、12、16、24、36、48h to measure pH、ammonia nitrogen (NH3-N)、microbial protein (MCP) and volatile fatty acids (VFAs). The results show that:(1) The addition of yeast caused an increase in pH values and the pH values in 0.1% group were significantly higher than those in control group (P<0.05). (2) The gas production was significantly increased by active dried yeast (P<0.05). (3) With the addition of active dried yeast increasing, the MCP concentration in test groups were improved. As the adding amount reached 0.1%, MCP concentration got peak value. (4) The active dried yeast caused a decrease of NH3-N content, and the content of 0.075%,0.1%,0.125% groups were significantly lower than those in control group (P<0.05). (5) The yeast supplementation tend to enhance the concentration of acetate, propionate, butyrate, total volatile fatty acid (TVFA) and reduce the acetate:propionate ratio significantly, respectively. Because of increasing propionate fermentation, ruminal energy efficiency was improved by yeast. (6)The appropriate level of active dried yeast for rumen fermentation was 0.1%, based on the indexes being synthesized.In Exp.2, on the basis of previous experiment, six Xuanhan yellow cattle (BW 457.80±18.15kg) with permanent rumen fistula divided into two treatments randomly. The present trial was designed to test the effect of yeast on dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) degradation of alfalfa particles, corn straw silage, rye hay and total mixed ration at 6, 12,24,36,48,72h by nylon bag technique. The experimental cattle were fed with basic diet and cattle in treatment group, in addition, were given 0.1% active dried yeast. There are 3 replications in each group and 1 cattle per replication. The adaptive period was 10 days and the experimental period lasted 3 d. The results show that:(1) The NDF, ADF, DM, CP rapid degraded fraction (a) of alfalfa particles, corn straw silage, rye hay and total mixed ration in rumen were enhanced significantly by adding active dried yeast (P<0.05). (2) The yeast caused a significant increase of NDF, ADF, DM, CP effective degradation rate of different roughages within 72h (P<0.05).In Exp.3, the experimental design is same with Exp.2. The adaptive period lasted 10 days and the trial period was 30 d. Rumen fluid and blood samples were collected at Id,15d and 30d to determine the effect of feeding active dried yeast on blood biochemical indexes and ruminal microbial community. The results show that:(1) the content of insulin (Ins) and insulinlike growth factor 1 (IGF-1) were significantly higher than control group (P<0.05). The dietary supplemental yeast, comparing to control group, caused significantly enhancement of blood albumin (ALB), globulin (GLB), total protein (TP) and glucose (GLU) concentration (P<0.05). Blood urea nitrogen (BUN) was decreased significantly by adding active dried yeast (P<0.05). (2) The supplementation of yeast increased pH values and decreased oxidation-reduction potential (ORP) value and lactate in rumen, respectively. (3) There were different degrees of the increase of ruminal cellulolytic bacteria (R.albus, R. flavefaciens, F.succinogenes, Butyrivibrio fibrisolvens) with the supplementation of active dried yeast. (4)Yeast, comparing with controls, inhibited the population of lactate-producing bacteria (streptococcus bovis) and improved lactate-utilizing bacteria (selenomonas ruminantium and megasphaera elsdenii) population. Meanwhile, population of fungus and protozoa in rumen were increased and methanogens was decreased.In conclusion, active dried yeast could increase pH value in rumen, maintain the ruminal anaerobic environment, improve ruminal fermentation, and thus increase rapid degraded fraction, effective degradation of roughages and decrease ruminal lactate concentration under high concentrate condition by decreasing population of lactate-producing bacteria (Streptococcus bovis) and stimulating cellulolytic bacteria community (R.albus, R. flavefaciens, F.succinogenes, Butyrivibrio fibrisolvens) and lactate-utilizing bacteria (Selenomonas ruminantium, Megasphaera elsdenii). Because of improvement of NH3-N utilization, MCP synthesis, VFAs concentration and propionate fermentation, glucose and nitrogen utilization and energy efficiency were improved by yeast. The appropriate supplementation of active dried yeast for ruminal fermentation was 0.1%, based on parameters of fermentation in vitro synthetically. |
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