| Subacute ruminal acidosis(SARA)is a common nutritional and metabolic disease in dairy cows.It is the accumulation of volatile fatty acid(VFA)in the rumen due to animal ingestion of high-concentrate feed containing a large amount of carbohydrate,which is easy to ferment.When the production of VFA such as lactic acid in the rumen exceeds the absorption or clearance rate of the rumen,the p H in the rumen decreases,thus,resulting in SARA.SARA is characterized by slow onset,long course and insidious symptoms,which can impair rumen function of dairy cows,seriously reduce feed utilization,leading to decreased milk yield and milk quality.SARA can also induce chronic diseases such as laminitis,intermittent diarrhea and systemic inflammation,and seriously harm long-term health and production performance of dairy cows,which causes huge economic losses.Therefore,scientific and effective SARA monitoring and diagnostic is of great importance.In this study,rumen fluid and blood of healthy cows and SARA cows were collected,and relevant indexes of rumen fluid and blood were detected and analyzed by biochemical analysis or ELISA,so as to determine the correlation between the indexes and p H of rumen fluid and screen potential sensitive indicators of SARA.The results showed that compared with healthy dairy cows,the p H of rumen fluid in SARA dairy cows was significantly decreased,and the levels of total VFA,acetic acid,isobutyric acid,lipopolysaccharide(LPS)and histamine in rumen fluid were significantly increased.The levels of total VFA,acetic acid,propionic acid,butyric acid,isobutyric acid,LPS and histamine in rumen fluid were negatively correlated with p H.The content of glucose(Glu),an indicator related to energy metabolism,in blood of SARA cows was significantly increased;immuno-related indexes LPS,lipopolysaccharide binding protein(LBP),interleukin-1β(IL-1β),tumor necrosis factor-α(TNF-α),haptoglobin(HP),serum amyloid protein A(SAA),neutrophilic granulocyte count and eosinophilic granulocyte count were significantly increased.The levels of LBP,IL-1β,TNF-α and SAA were negatively correlated with rumen fluid p H.Malondialdehyde(MDA)level was significantly increased,while superoxide dismutase(SOD),catalase(CAT)and glutathione peroxidase(GSH-Px)levels were significantly decreased.Moreover,MDA level was negatively correlated with rumen fluid p H.The levels of SOD,CAT and GSH-Px were positively correlated with rumen fluid p H.Comprehensive comparison showed that there was a strong correlation between total VFA,acetic acid,rumen fluid LPS,histamine,blood LPS,LBP,IL-1β,TNF-α,SAA,MDA,CAT,GSH-Px and rumen fluid p H,which could be used as an alternative sensitive index for the diagnosis of SARA.In addition,receiver operating characteristic curve(ROC curve)was used to analyze the area under the curve(AUC),sensitivity(sensitivity,Se),1-specificity(Sp)and cut-off point of specificity were used to compare the diagnostic value of these selected indicators in diagnosing SARA cows.The results showed that the AUC of total VFA in rumen was 0.843,that of acetic acid was 0.738,that of rumen fluid LPS was 0.938,that of histamine was 0.835,that of IL-1β was 0.730.The AUC of TNF-α was 0.785 and that of MDA was 0.884,which possessed practical diagnostic value.Among these,histamine(Se = 1,Sp = 0.4),IL-1β(Se = 0.85,Sp = 0.45),TNF-α(Se = 0.9,Sp = 0.4),MDA(Se = 0.95,Sp = 0.35)had diagnostic significance.The above results indicated that the relevant components of rumen fluid of SARA cows were significantly changed.SARA cows showed significant systemic inflammation and oxidative damage,as well as metabolic disorders to a certain extent.Histamine in rumen fluid,IL-1β,TNF-α and MDA in blood can be used as potential sensitive diagnostic indicators for SARA.This study aims to provide data basis for the development of sensitive and effective SARA monitoring and warning system and diagnostic means. |
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