EXOGENOUS CONTROL OF FOLLICULAR WAVE EMERGENCE IN CATTLE

Variability in ovarian response to superstimulatory treatments and in the interval from PGF(2 alpha) treatment to estrus in cattle is largely attributable to the status of follicular wave development at the time of treatment. To date, most treatments designed to control follicular wave development have been based on removal of the suppressive effect of the dominant follicle, either physically (by electrocauterization or ultrasound-guided follicle ablation) or hormonally (by GnRH or estradiol and progestogen treatment), and thereby induce the emergence of a new follicular wave at a specific time after treatment. Treatment of progestogen-implanted cattle with estradiol-17 beta (E-17 beta) resulted in suppression of the dominant follicle and emergence of a new follicular wave 4.3 +/- 0.1 d later. Superstimulatory treatments initiated 4 d after E-17 beta treatment in progestogen-implanted cattle resulted in a superovulatory response comparable to that of cattle in which superstimulatory treatments were initiated on the second follicular wave. In another study, induced follicular wave emergence, regardless of the stage of the estrous cycle, resulted in similar superovulatory response and higher fertilization rates in heifers than when superstimulatory treatments were initiated 8 to 12 d after estrus (traditional approach). Finally, estrus synchronization treatments with E-17 beta plus progesterone and PGF(2 alpha) have resulted in synchronous estrus and ovulation. Overall, it appears that treatment with E-17 beta and progestogen in combination may be used to effectively control and synchronize follicular wave development and may have important implications in artificial control of ovarian cyclicity and superovulation.