Response of suckling beef cows to multiple, low-dose injections of Gn-RH with or without progesterone pretreatment.

Treatment of 97 suckling beef cows at about 30 days post partum with doses of 0.25, 0.5, 1.0, 2.5, 3.0, or 5.0 micrograms Gn-RH/pulse for period of 2-4 days at 1-h or 2-h intervals in three different experiments did not increase the number of cows ovulating when compared to untreated controls. Treatment with 0.25 or 0.5 micrograms Gn-RH/pulse resulted in little or no LH release, whereas higher doses gave discernible LH releases after each Gn-RH pulse. Pretreatment with progesterone did not affect the ovulatory or LH responses. These data indicate that pulsatile injections of Gn-RH, at the dose levels and frequencies used, cannot reactivate ovarian cyclicity in a majority of cows. We suggest that the degree of follicular development at the time of treatment is a major factor determining the ovulatory response to such pulsatile Gn-RH regimens.