In this study, the presence of any relationships between the serum levels of progesterone, calcium, zinc, copper, magnesium and potassium during the oestrous cycles of a total of 14 animals (6 heifers, 8 cows) between January-February and July-August of 1996 was investigated.

The estrus cycles of the animals were synchronized using prostaglandin F-2 alpha and their blood samples were collected overnight during the cycle, starting on the following estrus of the synchronization. Serum Ca, Zn, Cu, K, Mg and progesterone levels were determined using atomic absorbtion unit and RIA, respectively.

In this respect, no difference was determined between cycle days of the levels of serum Ca, Zn, Cu, Mg and K during the oestrous cycle (P>0.05). When seasonal variation was taken into account, it was observed that mean serum levels of Ca and K were higher in summer season than the winter; whereas lower levels of Zn (P<0.05). Howewer, there was no seasonal variation in serum Cu, Mg and progesterone levels (P>0.05). A variation between cows and heifers were considered, higher serum Zn level was observed in cows than heifers (P<0.05). The differience between mean serum Ca, Cu, K, Mg and progesterone levels of these two groups was not significant (P>0.05).

There was a positive correlation between Cu-Zn in the winter season Ca-Zn, Ca-Cu and Cu-Zn in the summer season. Additionaly, a positive correlation seen between P4-Ca and Cu-Zn in the cows and P4-Cu, Cu-Zn and Ca-K in the heifers throughout the oestrous cycle.

In conclusion, despite the marked difference in serum progesterone levels between the various stages at oestrous cycle, the difference between the same stages of the oestrous cycle regarding to serum levels of Ca, Cu, Mg, Zn and K was observed to be not-significant.