Abstract
Peripheral blood hormonal patterns, follicular steroids and oocyte nuclear maturation were studied in dairy cows induced to superovulate with a PMSG/PG regimen and given a single dose of GnRH at the time of the expected LH surge. Animals can be divided into two groups according to the appearance of the LH surge after GnRH treatment. Group A can be characterized by a normal hormonal profile including the LH surge immediately after GnRH treatment. The majority of follicles and oocytes obtained from this group followed a normal maturation pattern. However, animals from Group B lacked the LH surge despite GnRH treatment, and their follicular and oocyte maturation was impaired. It is concluded that a single dose of GnRH given at the time of the expected LH surge is unable to challenge the LH surge in all PMSG-superovulated cows or to protect these animals from abnormal follicular and oocyte maturation. Such impaired maturation can cause poor oocyte and, subsequently, poor embryo quality in donor cows.
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