| The subacute rumen acidosis(SARA)have become a prevalent problem in the dairy herds exposed on a high amount of ruminally-available carbohydrate.This will result in the important economic loss associated with SARA in dairy herds.The objective of this study was(1)to understand the dynamic changes and correlations between blood lactic acid and other biochemical parameters and milk composition in dairy cows,(2)to demonstrate the regularity of the SARA development and(3)to choose reliable monitoring parameters which could conduce to the set up of the effective system of predicting and monitoring SARA in dairy herds.The study was divided into two parts:In the first part 19 dairy cows with non-clinical difference were randomly chosen;plasma lactic acid,non-esterified fatty acids, calcium,phosphonium,magnesium and potassium were dynamically determined,respectively at -7d(7d prepartum),0d(parturition day),7d,14d, 21d,28d,35d,42d,49d,56d postpartum.In the second part 18 dairy cows with non-clinical difference were randomly chosen,plasma lactic acid, endotoxin,non-esterified fatty acids and magnesium,and milk fat,milk solids-not-fat,protein content were determined at-7d(7d prepartum), 0d(parturition day),7d,14d,21d,28d,35d,42d,49d,56d,63d postpartum, respectively.In above two experiments the cows with high plasma level of lactic acid and relative signs of SARA were allocated to affected group,the remainder to control group.The following results were observed:1.The time for plasma parameters to increase to the abnormality in affected group:lactic acid in -7d～14d and 35d～49d,non-esterified fatty acids and endotoxin in 0d～ 14d,calcium in 0d～7d;the time for plasma parameters to decrease to the abnormality:phosphonium in 7d～21d.Normal fluctuations were observed in plasma magnesium and potassium.2.The time for milk composition content to decrease to the abnormality in affected group:milk fat in 14d～28d.The milk solids-not-fat and protein content abnormality were not observed during the experimental time.3.There were high positive correlations between plasma lactic acid and non-esterified fatty acids and between plasma lactic acid and calcium in affected group,respectively.Milk protein and milk solids-not-fat had positive correlation,but non-esterified fatty acids had negative correlation with phosphonium.4.The time for plasma lactic acid,non-esterified fatty acids and milk fat abnormality changing was longer,rumen function's modulation was slow and a rapid fluctuation was observed in affected dairy cows.5. SARA in dairy cows occurs approximately within 1 week prepartum,and 1, 5～7 weeks postpartum.Plasma lactic acid,non-esterified fatty acids and milk fat could be considered to monitor SARA efficiently,but endotoxin, calcium,phosphonium,magnesium and potassium could serve as auxiliary diagnostic methods of SARA in dairy cows. |
