This study was undertaken to examine serum and plasma Zn and Cu levels during different stages of oestrous cycle in cows. Presence of any differences in plasma and serum concentrations of these trace elements between various stages of the cycles were also investigated. A total of 32 Brown Swiss cows were used. The blood samples of 15 cows were used for serum and of remaining 17 cows for the plasma extraction. All animals were synchronised with PGF2a, and then randomly allocated into two groups. Commencing on the onset of the oestrous cycle, blood samples (10ml) at two days intervals were collected from the jugular veins of all cows for 21 days. Zn and Cu concentrations and progesterone (P) levels were determined using atomic absorption unit and RIA, respectively.

Serum Zn levels varied from 0.49 ± 0.07 to 0.68 ± 0.11mg/L and those of plasma from 0.74 ± 0.08 to 0.98 ± 0.17 mg/L. Cu levels were found to be between 0.67 ± 0.04 - 0.73 ± 0.05ng/L in serum and between 0.48 ± 0.03 - 0.54 ±0.02 ng/L in plasma. The results showed that plasma Zn levels were higher than those obtained from the serum on the days 4, 10, 16 and 18 of the oestrous cycle. Whereas serum Cu levels were found to be higher at all sampling intervals than those of plasma. There was a negative correlation between P4 levels and serum Zn concentrations throughout the oestrous cycle. It was concluded that Zn and Cu deficiency resulted in some fluctuations in plasma P4 levels. Unlike the well-documented variations in blood hormone levels, concentrations of Zn and Cu remained unchanged during the oestrous cycle.