Assessment of an immunoturbidimetric method for measuring equine serum haptoglobin concentrations

Serum haptoglobin was measured by immunoturbidity in Thoroughbreds stabled in three Newmarket yards for nine months. The mean serum haptoglobin value for horses housed in Stable 1 was 1.43 +/- 0.68 g/litre, similar to values in grazing adult ponies. The mean monthly haptoglobin values remained constant. For horses in Stable 2 there was an increase in serum haptoglobin values in June and July whereas, in Stable 3, the increases early in the training season were associated with an increase in serum viral titres. In equine serum, haptoglobin values estimated in g/litre by immunoturbidimetry were twice the haemoglobin binding capacity (HbBC). The correlation coefficient, between the methods, exceeded 0.96. Surgical interference caused a 2- to 3-fold increase in serum haptoglobin, with levels peaking between three and five days post surgery. The concomitant presence of haematomata following surgical interference (castration) resulted in the disappearance of haptoglobin from the circulation. There was no significant increase in serum haptoglobin levels following vaccination of Thoroughbreds against influenza and tetanus. However inhalation of influenza virus by vaccinated and non-vaccinated ponies resulted in a 2- to 3-fold increase in both groups of ponies, peaking seven to 10 days post infection. Serum haptoglobin proved to be a useful indicator of infection/inflammation and haemolytic disease in the horse and could be used to monitor the health status of stabled Thoroughbreds.