Effects of Directly Fed Yeast Culture on Ruminal Fermentation in Dairy Cows

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 (P0.05) 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% (P0.05) at 4 h.The concentrations of total ruminal volatile fatty acids,acetic acid,butyric acid,and acetate/propionate ratio were significantly increased (P0.05) 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 (P0.05),and rumen protozoa number was not altered by treatments (P0.05).All indices were not different among 3 treatments (P0.05).In conclusion,yeast culture affects rumen fermentation and consequently improves feed utilization.