本文旨在研究酵母培养物对奶牛瘤胃发酵功能的影响。试验选用4头装有永久性瘤胃瘘管、体况相近的荷斯坦奶牛，直接饲喂50 g/d酵母培养物，试验分为对照组、扣囊酵母（Sacchromycopsis fibuligera，SF）组、酿酒酵母(Saccharomyces cerevisiae，SC)组和热带假丝酵母(Candida tropicalis berkhout，CB)组。采用4×4拉丁方试验设计，试验分为4期，每期18 d（预试期15 d，正试期3 d）。结果表明：饲喂酵母培养物4~8 h均能显著提高瘤胃pH（P<0.05），其中CB组效果最好，可以把pH从6.24提高到6.45~6.59，在饲喂4 h后，酵母培养物将氨态氮浓度显著提高了11.64%~16.09%（P<0.05），并在6~8 h时，显著提高瘤胃总挥发性脂肪酸、乙酸、丁酸浓度和乙酸/丙酸比值（P<0.05）。在4~8 h，酵母培养物能显著提高瘤胃液中细菌总数25.00%~59.25%和纤维素酶的活性6.13%~11.83%（P<0.05），但酵母培养物对瘤胃原虫数量没有显著影响（P>0.05）。各指标3种酵母菌组间差异不显著（P>0.05）。酵母培养物直接饲喂奶牛，可以改善瘤胃内环境指标，从而提高饲料利用效率。

This study was conducted to examine the effects of yeast culture on rumen fermentation when fed to dairy cows directly. Four ruminally-fistulated Holstein cows were used in 4×4 Latin square design. Each cow was directly fed one of the diets (50 g/d): no addition (the control), Sacchromycopsis fibuligera (SF), Saccharomyces cerevisiae (SC), and Candida tropicalis Berkhout (CB). The whole trial lasted for 18 d with 15 d of adaptation period and 3 d of sampling period. The results showed as follows: dietary yeast culture could significantly increase rumen pH (P<0.05) at 4-8 h, with CB yeast culture being the best, which could increase pH from 6.24 to 6.45-6.59. Dietary yeast culture also significantly increased the concentration of ammonia nitrogen by 11.64%-16.09% (P<0.05) at 4 h. The concentrations of total ruminal volatile fatty acids, acetic acid, butyric acid, and acetate/propionate ratio were significantly increased (P<0.05) when cows fed yeast culture at 6-8 h. Total number of rumen bacteria and cellulase activity were significantly increased by 25.00%-59.25% and 6.13%-11.83% at 4-8 h, respectively (P<0.05), and rumen protozoa number was not altered by treatments (P>0.05). All indices were not different among 3 treatments (P>0.05). In conclusion, yeast culture affects rumen fermentation and consequently improves feed utilization.［Chinese Journal of Animal Nutrition, 2010，22（5）:1390-1395］