MEASUREMENT OF PARATHYROID-HORMONE IN HORSES

Measurement of parathyroid hormone (PTH) in horses was performed on pl asma samples using 2 immunoradiometric assays: a human intact PTH assa y and a rat amino-terminal PTH assay. The assays were validated by ass essment of their precision, sensitivity and specificity, and also by e valuating PTH changes in the horse in response to variation in blood i onised calcium. Intra- and inter-assay variance, precision and sensiti vity were similar for both human and rat assays; however, the rat assa y was slightly more precise and sensitive than the human assay. Both a ssays detected an increase in PTH levels in the horse when blood ionis ed calcium was decreased and a decline in PTH concentration with hyper calcaemia. Measurement of PTH concentration in samples from healthy ho rses with the human assay yielded a mean (+/- s.e.) value of 31.3 +/- 4.1 pg/ml. When using the rat assay, PTH values were 44.1 +/- 5.3 pg/m l. Plasma samples held for up to 3 months at -20 degrees C did not sho w a significant change in PTH concentration. In conclusion, the human intact PTH and the rat amino-terminal assays detected equine PTH and c an be used for measurement of this hormone in horses. Quantification o f equine PTH using these assays will allow more precise diagnosis of a variety of disorders affecting mineral metabolism in horses.