Pituitary and ovarian responses to gonadotropin releasing hormone, calf removal and progestogen in anestrous beef cows.
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Biomedical subjects
Publications and source records attributed to E K Inskeep.
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Ten veterinarians diagnosed and treated 296 cows for reproductive irregularities on 28 dairy farms. Average interval from treatment with 25 mg of prostaglandin F2 alpha (137 cows) to estrus for cows with a corpus luteum (14.6 days) was reduced compared to saline (52 cows) (21.8 days), and a greater percentage (41.6 versus 17.3%) showed estrus within 6 days of treatment. Cows with a cystic corpus luteum (28) were detected in estrus at comparable intervals after prostaglandin F2 alpha or saline (21.8 versus 21.2 days), and similar proportions of cows were detected in estrus within 6 days of treatment (16.7 versus 10.0%). Intervals to estrus among cows with cystic follicles (40 cows) or anestrous cows with follicular ovaries (39 cows) did not differ after treatment with saline or 100 or 200 micrograms of gonadotropin releasing hormone. Within 25 days after treatment, 47.5% of cows with cystic ovaries and 64.1% of anestrous cows showed estrus. Number of cows pregnant after as many as three artificial inseminations of the number examined was 46%, whereas average number of conceptions per service was .32. The long interval from parturition to examination (112 days), the low rate of estrous response after treatment, and the long interval (1.6 estrous cycles) between estruses are consonant with inadequate estrous detection.
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Seventy-three multiparous beef cows (21 to 35 d postpartum) were used in an experiment with a 2 X 4 factorial design to test the effects of pretreatment with norgestomet and preovulatory gonadotropic stimulation on the life span of corpora lutea induced by human chorionic gonadotropin (hCG). Cows were implanted subcutaneously for 9 d with norgestomet (3 mg; 35 cows) or sham-implanted (38 cows). HCG (1,000 IU) was administered in to all cows 36 h (time = 0) after implant removal. Each cow received one of the following treatments: (1) pregnant mare's serum gonadotropin (PMSG; 750 IU) in a single subcutaneous injection 48 h prior to hCG (-48 h); (2) follicle stimulation hormone (FHS-P) in saline (10 mg) in a series of four subcutaneous injections (2.5 mg/injection) at -48, -36, -24 and -12 h; (3) FSH-P in 5% beeswax-sesame oil (10 mg) administered as in 2; or (4) saline, administered as in 2. Samples of serum taken at the time of implantation, at the time of implant removal and daily on d 5 to 20 after administration of hCG were assayed for progesterone. Samples taken at 12-h intervals from -48 to +12 h were assayed for estradiol-17 beta. Cows were observed for estrus at 6-h intervals from 24 to 60 h after implant removal and twice daily until d 22. Seventy-one percent of the cows (25/35) were in standing estrus from 29 to 60 h after removal of a norgestomet implant, compared to 16% of the sham-implanted cows (six of 38). As determined by progesterone in serum and by palpation of the ovaries, 88% of the cows (64/73) formed corpora lutea in response to hCG, with a tendency (P less than or equal to .10) for a positive effect of pretreatment with norgestomet (94 vs 82%). The life span of corpora lutea was longer (P less than or equal to .01) in cows treated with norgestomet (19.6 d) than in sham-implanted cows (13.4 d). Level of function of the induced corpora lutea as indicated by the pattern of daily concentrations of progesterone in serum was increased by pretreatment with either norgestomet (P less than .01) or gonadotropin (P less than .05), but there was no interaction of these treatments. The mean level of estrogen before ovulation was increased (P less than .01) by pretreatment with norgestomet or any regimen of gonadotropin, and, again, there was no significant interaction. Pretreatment with progestogen was associated with a higher pattern of concentration of estrogen over time (P less than .01).
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Two studies were conducted to investigate the effect of a progesterone-releasing intrauterine contraceptive device (IUD) on uterine secretion of prostaglandin (PG) F2alpha associated with IUD-induced luteolysis in sheep. In bilaterally ovulating ewes receiving an IUD on day 3 (estrus = day 0) intrauterine release of progesterone (90 microgram per day) by the device did not prevent premature luteolysis or the increased concentration of PGF2alpha in uterine venous plasma on day 5 caused by conventional IUD's. In the second study a progesterone-releasing IUD (645 microgram per day) inserted adjacent to the intact ovary at unilateral ovariectomy on day 14 inhibited early luteolysis in the subsequent estrous cycle and reduced the uterine secretion of PGF2alpha on day 5, without affecting concentrations of progesterone in the peripheral circulation at the intervening estrus. It is suggested that locally delivered intrauterine progesterone can inhibit IUD-induced luteolysis in the ewe by suppressing the uterine secretion of PGF2alpha.
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