R.E. Stewart

Administering a GnRH agonist (receptal) after insemination fails to improve pregnancy rates at first service

Two experiments were performed to determine the influence of administering a highly potent agonist of gonadotropin-releasing hormone (Receptal) on various reproductive characteristics in dairy cows. In Experiment 1, lactating Holstein cows were treated with either saline (n = 51) or 8 μg of receptal (n = 50) on d 11 to 14 after estrus (d 0) and first service. Peak concentrations of LH, FSH, and progesterone, but not estradiol-17β, in blood serum were increased during 6 to 12 h after injection of Receptal. Pregnancy rates were unaffected by treatment. Concentrations of progesterone in blood serum were increased in nonpregnant and pregnant cows after injection of Receptal. Return to estrus in Receptal-treated cows increased by 2.5 ± .8 days compared to controls. The number of follicles >10 mm in diameter, assessed by transrectal ultrasonography, were reduced and follicular development was altered after Receptal. In Experiment 2, various doses of Receptal were tested in eight dairy herds, including 1,013 inseminations at first service. Cows were given a single injection of either saline or 4, 8, or 12 μg of Receptal on days 11 to 14 after first service. Pregnancy rates were not improved consistently in all herds and failed to increase across all herds. We concluded that administering a potent GnRH agonist altered number and distribution of ovarian follicles, increased cycle length, and increased concentrations of progesterone, without a consistent increase in fertility.

Induction of estrus in thyroidectomized-ovariectomized, nonlactating, holstein cows

Low thyroid activity (hypothyroidism) has been reported to decrease sexual behavior associated with reproduction in several species. Using estradiol benzoate (EB) and progesterone (P ), we attempted to induce 4 estrus in hypothyroid cows. Thyroid glands (thyroidectomy) and ovaries (ovariectomy) were removed surgically from nonlactating and nonpregnant Holstein cows that were culled from the Kansas State University dairy herd. Eight cows were thyroidectomized and ovariectomized (THYOVEX) and another four cows were ovariectomized only (OVEX). Starting 9 hr after injection of EB, cows were continuously observed for estrus for 36 hr. Frequencies of mounting activity and standing behavior were recorded for each cow. The percentage showing standing estrus was greater in cows that had no thyroid glands or ovaries than in cows without ovaries (78 vs 31%). Manifestation of estrus was identical in cows treated with EB or EB+P (62%). Interval from 4 EB injection to onset of standing estrus, frequency of mounting activity, and duration of standing estrus were similar among treatment groups and unaffected by the type of hormonal treatment. Thyroidectomized cows can exhibit estrous behavior, which is similar to that in ovariectomized cows treated with EB or P +EB. 4

Influence of prebreeding progesterone plus prostaglandin F2-alpha on estrus and fertility in lactating dairy cows

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Concentrations of progesterone and conception rates in Holstein heifers after hCG administration during the first 3 weeks after estrus

This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright 1987 Kansas State University Agricultural Experiment Station and Cooperative Extension Service.

Further studies utilizing hormones to alter estrous cycles and fertility

In one large dairy herd, we examined the reproductive performance of 943 cows following early postpartum hormonal therapy utilizing gonadotropin-releasing hormone (GnRH or Cystorelin®) and prostaglandin F2-α (PGF). None of our hormonal treatments improved reproductive efficiency in this herd, whereas earlier studies at the KSU Dairy Teaching and Research Center had proved beneficial. However, cows given PGF to induce estrus at the beginning of the breeding period had similar reproductive performance to control cows, suggesting a potential use for one injection of PGF to allow the breeding of more cows by a target date after calving (e.g., by 65 days).; Dairy Day, 1987, Kansas State University, Manhattan, KS, 1987;

Influence of multiple daily injections of oxytocin on reproductive and milk characteristics of postpartum dairy cows

Release of oxytocin at the time of suckling or milking may delay onset of estrous cycles in postpartum cows. Twenty lactating Holsteins were used in this study to determine if multiple daily injections of oxytocin would prolong postpartum anestrus. Cows received either oxytocin or saline (controls) intravenously through indwelling jugular catheters four times daily for 28 days following calving. Treatment with oxytocin did not lengthen intervals to ovulation or estrus or alter secretion patterns of luteinizing hormone, cortisol, progesterone, or 13,14-dihydro-15-keto prostaglandin F2αin serum. Although milk production, percentage protein, and somatic cell counts were similar between treatment groups, oxytocin appeared to increase (P<.10) percentage of fat 0.99 vs 3.68%) in milk. Involution of the reproductive tract (uterus and cervix) was also similar between oxytocin-treated and control cows. We concluded that oxytocin alone does not prevent the occurrence of estrus and ovulation in dairy cows or hasten the rate of cervical and uterine involution.; Dairy Day, 1986, Kansas State University, Manhattan, KS, 1986;