饲粮精粗比和添加硫胺素对奶牛体外瘤胃发酵参数及菌群结构的影响

Effects of Dietary Concentrate to Forage Ratio and Thiamine Supplementation on in Vitro Rumen Fermentation Parameters and Microbial Community Structure in Dairy Cows

本试验采用体内逐渐提高奶牛饲粮精料水平与体外批次培养相结合的方法建立亚急性瘤胃酸中毒模型,旨在研究不同精粗比饲粮对硫胺素微生物净合成量的影响,以及添加硫胺素对亚急性瘤胃酸中毒状态下奶牛体外瘤胃发酵参数和菌群结构的影响。试验采用2×4因子完全随机试验设计,因素1为硫胺素添加水平,设0和180 mg/kg 2个水平,因素2为饲粮的精粗比,设4个水平,分别为40∶60、50∶50、60∶40、70∶30。试验共设8个处理,每个处理3个重复,于体外培养0、3、6、9、12 h后采集样品。结果表明:随着精料水平的提高,培养液中硫胺素的微生物净合成量呈先升高后降低的趋势,其中精粗比为40∶60、70∶30的饲粮组培养液中硫胺素的微生物净合成量在3、9、12 h时均显著或极显著低于精粗比为50∶50和60∶40的饲粮组(P<0.05或P<0.01)。在12 h时,随着精料水平的提高,培养液pH极显著降低(P<0.01),精粗比为70∶30的饲粮组发生亚急性瘤胃酸中毒;与未添加组相比,添加硫胺素组培养液pH极显著提高(P<0.01)。在6、9、12 h时,精粗比为60∶40和70∶30的饲粮组培养液中乳酸浓度极显著高于精粗比为40∶60的饲粮组(P<0.01);在3、9 h时,添加硫胺素可极显著降低培养液中乳酸浓度(P<0.01)。饲粮精粗比对培养液中溶纤维丁酸弧菌和反刍兽新月形单胞菌的数量无显著影响(P>0.05),但可显著或极显著影响培养液中牛链球菌、乳酸杆菌和埃氏巨型球菌的数量(P<0.05或P<0.01);与未添加组相比,添加硫胺素组培养液中牛链球菌的数量降低了3.84%(P<0.01),埃氏巨型球菌的数量提高了4.02%(P<0.01),但乳酸杆菌、溶纤维丁酸弧菌和反刍兽新月单胞菌的数量未发生显著变化(P>0.05)。由此得出,在高精料饲粮条件下,瘤胃中硫胺素的微生物净合成量降低,发生亚急性瘤胃酸中毒;添加硫胺素可通过提高瘤胃pH,降低乳酸浓度,以及调节瘤胃菌群结构来缓解亚急性瘤胃酸中毒。

A subacute ruminal acidosis（SARA） model was established by gradually increasing the dietary concentrate to forage ratio（C∶ F） of dairy cows in vivo combined with in vitro batch culture,aimed at determining the effects of dietary C∶ F on microbial net synthetic quantity of thiamine,and the effects of thiamine supplementation on in vitro rumen fermentation parameters and microbial community structure in dairy cows under the state of SARA.A 2×4 two factorial random experiment design was adopted： one factor was thiamine supplemental level（2 levels,0 and 180 mg/kg,respectively）,and the other was different dietary C∶ F（4 levels,40∶ 60,50∶ 50,60∶ 40 and 70∶ 30,respectively）.There were 8 treatments in the experiment and 3 replicates in each treatment,and samples were collected at 0,3,6,9 and 12 h after culture in vitro.The results showed as follows： with the concentrate level increasing,microbial net synthetic quantity of thiamine in culture solution was firstly increased and then decreased,and it was significantly lower in the groups with the dietary C∶ F of 40∶ 60 and 70∶ 30 than the other two groups at 3,9 and 12 h（P0.05 or P0.01）.The pH in culture solution was significantly decreased with the increase of dietary concentrate level at 12 h（P0.01）,and the SARA was occurred under the dietary C∶ F of 70∶ 30.The pH in culture solution in the thiamine supplemental group was significantly increased compared with the non-thiamine supplemental group（P0.01）.The lactate concentration in culture solution in the two groups with the C∶ F of 60∶ 40 and 70∶ 30 was significantly higher than that in the group with the dietary C∶ F of 40∶ 60（P0.01） at 6,9 and 12 h,and thiamine supplementation could significantly reduce the lactate concentration in culture solution at 3 and 9 h（P0.01）.Dietary C∶ F showed significant effects on the number of Strepococcus bovis,Lactobacillus and Megasphaera elsdenii in culture solution（P0.05 or P0.01）,but had no significant effects on the number of Butyrivibrio fibrisovens and Selenomonas ruminantium in culture solution（P0.05）.Meanwhile,the number of Strepococcus bovis was decreased by 3.84%（P0.01） and the number of Megasphaera elsdenii was increased by 4.02%（P0.01） in thiamine supplemental group compared with the non-thiamine supplemental group,while the number of Lactobacillus,Butyrivibrio fibrisolvens and Selenomonas ruminantium had no significant changes（P0.05）.It is concluded that the microbial net synthetic quantity of thiamine is decreased and the SARA is occurred under the high concentrate diets.Thiamine supplementation can relive SARA by increasing the rumen pH and declining the lactate concentration,and regulating rumen microbial community structure.