Course of blood levels of calcium, inorganic phosphate, alkaline phosphatase, parathyroid hormone and calcidiol (25-OH-D3) in one and two year old thoroughbred horses

The present study was aimed to determine the contents of calcium, inorganic phosphate, parathormon, 25-OH-D3 and the activity of alkaline phosphatase in the plasma of one- and two-years-old thoroughbred horses. Data were obtained monthly from 44 one-year-old thoroughbred of 4 different studs from May during grazing-season and from October during stable-, resp. training-season up to april of the following year. Calcium, inorganic phosphate and the activity of alkaline phosphatase were measured with a photometric method and the concentration of PTH and 25-OH-D3 were determined with a radioimmunoassay. The following results were obtained: Calcium: The concentration of calcium in the plasma of one-year-old thoroughbred horses was 3.03 +/- 0.23 mmol/l during grazing-season and 3.14 +/- 0.14 mmol/l during the following stable-, resp. training-season. Inorganic phosphate: The concentration of inorganic phosphate was significantly affected by the age. The average was 1.7 +/- 0.19 mmol/l during grazing-season and 1.3 +/- 0.19 mmol/l during the following stable- and training-season. Activity of alkaline phosphatase: The activity of alkaline phosphatase was also significantly affected by the age. The average of the activity was 403 +/- 86 U/l during grazing-season and 308 +/- 65 U/l during the following winter period. Parathormon: There were big differences between the averages of parathormon during grazing-season (1.27 +/- 0.45 ng/ml) and the following winter-season (0.9 +/- 39 ng/ml). Besides from that there were big individual differences. 25-OH-D3: The concentration of 25-OH-D3 during grazing-season (10.38 +/- 3.08 ng/ml) was lower than during the winter period (13.03 +/- 2.86 ng/ml). The significance of the obtained results is discussed in relation to the corresponding literature.