QUANTITATIVE-DETERMINATION OF BOVINE SERUM HAPTOGLOBIN IN EXPERIMENTALLY-INDUCED ESCHERICHIA-COLI MASTITIS

A high performance liquid chromatography (HPLC) method was developed, validated and used to analyse haptoglobin concentrations in serum samp les taken from eight cows which had been challenged twice intramammari ly with Escherichia coli. The results of the HPLC were compared with t hose from a photometric assay. The kinetics of the haptoglobin respons e were analysed with pharmacokinetic computer software. In contrast wi th the photometric assay, the HPLC was sufficiently sensitive to detec t normal background levels of bovine serum haptoglobin. The serum hapt oglobin concentrations of healthy cows ranged from 22 to 47 mg litre(- 1). As the concentration of haptoglobin increased, the results of the two methods correlated well (r=0.96). A 52-fold increase in serum hapt oglobin was detected after the first challenge with E coli. The mean p harmacokinetic parameters of the response after the first challenge we re: lag phase 12 hours, t(2/1increase) 20 hours, t(max) 72 hours, t(1/ 2increase) 46 hours, and mean residence time 112 hours. The second cha llenge three weeks later resulted in a significantly lower haptoglobin response, the area under curve being 35 per cent of that after the fi rst challenge. The clinical signs and inflammatory changes in the milk did not differ significantly between the challenges.