Abstract: 【Objective】 This study aimed to investigate the correlation between blood biochemistry,immunity,oxidative stress,metabolic products,urinary biochemical metabolism,milk composition and rumen pH in dairy cows with subacute ruminal acidosis (SARA),in order to screen potential auxiliary indicators for effective diagnosis and monitoring of SARA dairy cows. 【Method】 Sixteen Holstein dairy cows in good body condition with similar number of litres (2-3),body weight (580 kg±20 kg),days of lactation (130 d±33 d) and milk yield (21.28 kg/d±3.78 kg/d) were selected and divided into two groups i.e.,control (CON) group and SARA group with 8 dairy cows in each group.Dairy cows in CON group were fed a basal diet with 5∶5 concentrate to forage ratio.Dairy cows in SARA group was supplemented with pressed corn (1 kg/d) on the basis of CON group,and the diet concentrate to forage ratio was 6∶4,and the experiment lasted for 60 days.Rumen pH was the gold standard for detecting SARA in dairy cows.SmaXtec equipment was used to monitor rumen pH,and Pearson correlation coefficient (r) was used to analyze the correlation between body fluid index of SARA dairy cows and rumen pH. 【Result】 ①The daily duration of rumen pH below 5.5 and 5.8 in SARA group was 2.55 and 6.38 h,respectively,indicating that the SARA model was successfully established.②Compared with CON group,the contents of albumin (ALB),interleukin-1β (IL-1β),tumor necrosis factor-α (TNF-α),malondialdehyde (MDA) and amyloid A in SARA group were significantly increased,and were negatively correlated with rumen pH (P＜0.05).The activities of superoxide dismutase (SOD),glutathione peroxidase (GSH-Px),peroxidase (POD) and catalase (CAT) were significantly decreased,and were positively correlated with rumen pH (P＜0.05).③Compared with CON group,the contents of C16∶0,C18∶0,C18∶2 and C20∶1 in SARA group were significantly decreased,which showed a significant positive correlation with rumen pH (P＜0.05).Whereas,the contents of tyramine,cadaverine,histamine and lipopolysaccharides were significantly increased,which showed a significant negative correlation with rumen pH (P＜0.05).④Compared with CON group,the contents of L-cystine and L-glutamic acid in SARA group were significantly increased,which was significantly negatively correlated with rumen pH (P＜0.05).The contents of tryptophan and threonine were significantly decreased,which were significantly positively correlated with rumen pH (P＜0.05).⑤Compared with CON group, urinary pH,and the contents of calcium and creatinine in SARA group were significantly decreased,which showed a significant positive correlation with rumen pH (P＜0.05).Whereas,the contents of phosphorus and uric acid were significantly increased,which showed a significant negative correlation with rumen pH (P＜0.05).The milk fat rate in emulsion was significantly decreased,which showed a significant positive correlation with rumen pH (P＜0.05),whereas the number of somatic cell counts was significantly increased (P＜0.05),which was significantly negatively correlated with rumen pH (P＜0.05). 【Conclusion】 By Pearson correlation coefficient analysis with |r|＞0.85 as the screening basis,the contents of SOD,GHS-Px,POD,MDA,C18∶2,tryptophan and histamine in serum,urinary pH,milk fat rate in emulsion,and somatic cell counts correlated with rumen pH,which were of reference value for the diagnosis and monitoring of SARA dairy cows,and could be used as potential ancillary diagnostic index for SARA in dairy cows.

Key words: subacute ruminal acidosis; dairy cows; body fluid index; pH; correlation; ancillary diagnostic index