Serum cortisol concentrations in spanish mares during pregnancy

The aims of this study were to define the normal serum concentrations of cortisol in Spanish mares, and to analyse the effect of pregnancy and age. Thirty-three Spanish broodmares, aged between 4 and 17 years were studied. Jugular blood samples were extracted every month during pregnancy, in the morning. Immediately after withdrawal, blood was centrifuged and serum was harvested. Serum cortisol concentrations were measured by competitive immunoassay. Mean serum cortisol concentrations were 54.96 ng/ml, with maximum and minimum values of 281.31 and 4.21 ng/ml respectively. Serum cortisol concentrations during the first half of pregnancy were significantly higher than those of the second half Mean values in the first month of pregnancy were 58.43 ng/ld. They increased progressively (P < 0.05), achieving maximum concentrations at 4(th) (74.05 ng/ml) and 5(th) (75.64 ng/ml) months. A significant decrease was observed from the 7(th) month to the end of pregnancy, with the minimum values (P < 0. 05) in the last three months (32.46, 34. 10 and 28.77 ng/ml at 9(th), 10(th) and 11 (th) months). No significant differences existed in relation to the age of the mares. This research demonstrated that serum cortisol concentrations in pregnant Spanish broodmares are similar to the normal values described for adult healthy horses. Furthermore, pregnancy induces significant changes, in serum cortisol concentrations. This finding might be the consequence of the interaction between metabolism and reproductive hormones during pregnancy.