Abstract: The quantitative changes of some related bacteria in the rumen of dairy goats suffered from subacute rumen acidosis (SARA) were determined. Six Guanzhong lactating goats with similar weights and fixed with ruminal cannula were used.They were fed concentrates daily by gradually increasing feeding regime. The trial was divided into four stages and in first stage dietary concentrate-to-forage ratio is 5∶5, in second stage 6∶4, in third stage 7∶3，and in the fourth stage 8∶2. The amount of ruminal bacteria of the experimental animals were determined by the method of 16S rRNA probes and traditional cultivation method. With the increase of the dietary concentrate to forage ratio, the quantities of Strepococcus bovis, Lactobacillus, Selenomonas ruminantium, Megasphera elsdenii and Amylolytic bacteria were increased in varying degrees, while amounts of the three kinds Cellulolytic bacterias were decreased and the numbers of amylolytic bacteria increased significantly（P<0.01）.Under the condition suffered from SARA, the amounts of rumen bacteria, Lactate-production bacteria and Lactate-utilizing bacteria were all increased, and quantities of the three main kinds Cellulolytic bacterias were decreased significantly.

Key words: subacute rumen acidosis; ruminal bacteria; 16S rRNA probes