In this study, the levels of serum progesterone, vitamin A, ß-carotene and magnesium (Mg) in 12 cows during pregnancy period and after delivery were determined and their interrelationships were evaluated.

Serum vitamin A and ß-carotene, and progesterone levels were assessed with spectrophotometer device, Atomic absorption spectrophotometer and enzyme immunoassay method, respectively.

The progesterone concentration increased slightly (3.02±0.35 ng/ml) at the 2^nd month of pregnancy, declined (2.43±0.24-2.44±0.24 ng/ml) between 3-6 months, increased sharply (3.36±0.22 ng/ml) at the 7^th month, reached its peak value (3.79±0.35 ng/ml) at 8^th month and then declined below 1 ng/ml a day after parturition. The present results revealed that gestation had a significant (P<0.001) effect on concentrations of serum progesterone, vitamin A, β-carotene and Mg. A positive correlation was found between serum progesterone and Mg (P<0.01), progesterone and vitamin A (P<0.05) or progesterone and β-carotene (P<0.05) during gestation. Additionally, there was an important correlation between serum vitamin A and ß-carotene during pregnancy (P<0.01).

In conclusion, the present findings suggest that serum progesterone, vitamin A, ß-carotene and Mg concentrations of the cows similarly fed, could alter depending on gestation period and parturition.