[Comparison of different methods for monitoring of acid base status in dairy cow herds]

Acid-base disorders in dairy herds can be diagnosed by determining urinary net base excretion (NBE). Modifications of this method are the differential NBE (dNBE) with determination of the urinary concentration-independent base-acid ratio (BAR) and the simplified NBE test with reduced urine volume (sNBE). The aim of this study was to compare these methods among themselves and as a pooled test, in their assessment of cow group acid base status as well as to derive recommendations for practical use.

The concentrations of NBE, dNBE, and sNBE were measured in urine samples derived from 855 German-Holstein cows in 127 cow groups at different stages of lactation. BAR was then calculated. dNBE and BAR were determined both individually per cow and as a pool of a group. Mixed linear models were used to examine the relationship between the mean of the individual animal values and the pool sample result of a group for these two parameters. In addition, all groups were evaluated with respect to acidotic or alkalotic load based on their single animal results of the respective methods, the mean values formed from them, and the measured pool result. By using the single animal BAR as reference, the sensitivity and specificity of the different methods were calculated.

The calculated mean values of the individual measurements of dNBE and BAR differed from the measured value in the pool sample, especially in low and high measurement ranges. In the group assessment, NBE showed the best combined sensitivity and specificity for the detection of acid base disorders. The dNBE pool assay showed satisfactory specificity with respect to acidosis and alkalosis, while the sNBE on an individual animal basis and the BAR determination in the pool showed satisfactory sensitivity with respect to acidosis.

It was shown that NBE determined in individual animal samples is well suited for the assessment of acid base status of cow groups and can therefore be recommended for practical use. The determination of dNBE as well as BAR as a pool test is not sufficient for the detection of alkalotic load in cow groups but may help to confirm an existing acidotic load.