中文摘要：

本试验旨在研究不同水平的包被维生素A对奶牛瘤胃发酵特性及营养物质表观消化率的影响.试验采用单因素随机区组试验设计,按照体重、产奶量及胎次相近的原则,将28头奶牛随机分为2组,每组14头,各组在基础饲粮中分别添加110和220 IU/kg BW包被维生素A,基础饲粮精粗比为42：58.预试期15d,正试期60 d.结果表明：与110 IU/kg BW组相比,220 IU/kg BW组能够显著增加奶牛瘤胃液中维生素A含量和丙酸浓度（P＜0.05）,显著提高粗脂肪的表观消化率（P＜0.05）;包被维生素A对瘤胃液pH,氨氮和菌体蛋白含量,乙酸、丁酸和总挥发性脂肪酸浓度,乙酸/丙酸以及中性洗涤纤维、钙、磷的表观消化率均无显著的影响（P＞0.05）.结果提示,在NRC（2001）推荐量（110 IU/kg BW）基础上,进一步增加包被维生素A水平到220 IU/kg BW,对奶牛瘤胃发酵功能无显著的影响,但可促进奶牛对粗脂肪的消化,增加瘤胃液中维生素A含量和丙酸的浓度.

英文摘要：

This study was conducted to determine the effects of different levels of coated vitamin A on ruminal fermentation characteristics and nutrient apparent digestibility of dairy cows.Twenty-eight Holstein cows were used in a single factor randomized block arrangement and were divided into 2 groups with 14 replicates in each group by the principle of similar body weight,milk yield and parity.Coated vitamin A at two levels （110 and 220 IU/kg BW,respectively） was supplemented to a basal diet （concentrate ∶roughage was 42∶58）.Pre-trial period was 15 days and trial period was 60 days.The results showed as follows：compared with 110 IU/kg BW group,vitamin A content,propionate acid concentration and ether extract apparent digestibility in rumen fluid in 220 IU/kg BW group could be significantly increased （P＜0.05） ; There were no significant effects of coated vitamin A on pH,the contents of ammonia nitrogen and bacterial protein,the concentrations of acetic acid,butyric acid and total volatile fatty acids,acetic acid/propionic acid,and the digestibility of neutral detergent fi-ber,calcium and phosphorus （P＞0.05）.Based on recommend requirement in NRC （2001） （110 IU/kg BW）,further increased coated vitamin A level to 220 IU/kg BW can promote digestion of ether extract and increase vitamin A content and propionate acid concentration in rumen fluid without affecting the function of ruminal fermentation.