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.
D000818:Animals; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005260:Female; D007774:Lactation; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D010060:Ovulation / Q000187:drug effects*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology*; D013997:Time Factors
D010906:Pituitary Hormone-Releasing Hormones; D011374:Progesterone; D007986:Luteinizing Hormone