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

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Abstract
Treatment of 97 suckling beef cows at .apprx. 30 days post partum with doses of 0.25, 0.5, 1.0, 2.5, 3.0 or 5.0 .mu.g Gn-RH[gonadotropin releasing hormone]/pulse for period of 2-4 days at 1h or 2h intervals in 3 different experiments did not increase the number of cows ovulating when compared to untreated controls. Treatment with 0.25 or 0.5 .mu.g Gn-RH/pulse resulted in little or no LH [luteinizing hormone] release, while higher doses gave discernible LH releases after each Gn-RH pulse. Pretreatment with progesterone did not affect the ovulatory or LH responses. Pulsatile injections of Gn-RH, at the dose levels and frequencies used, cannot reactivate ovarian cyclicity in a majority of cows. Apparently the degree of follicular development at the time of treatment is a major factor determining the ovulatory response to such pulsatile Gn-RH regimens.