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

Summary. 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 µg 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 µg 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.