AbstractsMedical & Health Science

The overall objective was to develop new synchronization protocols that facilitate fixed-time artificial insemination (AI). A series of experiments were designed to evaluate the effects of estradiol and progesterone on gonadotrophin release, follicular wave emergence and ovulation in beef cattle. In ovariectomized cows, a new CIDR-B device increased plasma progesterone to near-luteal concentrations, but for only 2 to 3 days. Injection of 100 mg progesterone increased plasma progesterone approximately 2 ng/mL. Progesterone suppressed plasma LH concentrations but did not affect plasma FSH concentrations. Estradiol, with or without progesterone, resulted in FSH suppression with resurgence (and follicular wave emergence) at an interval that varied according to the estradiol formulation. Estradiol administration following CIDR-B removal resulted in LH release (and ovulation in intact animals). Both estradiol-17β and estradiol benzoate (EB) synchronized ovarian follicular wave emergence in CIDR-B�-treated animals and the interval from CIDR-B removal to ovulation (72 to 120 h) was shorter and more synchronous in estradiol-treated animals than in controls. In cattle given a CIDR-B device and estradiol plus progesterone, estradiol treatment following CIDR-B removal 7 days later resulted in acceptable conception rates to fixed-time AI. Estradiol or GnRH at the beginning and end of a 7-day MGA-based synchronization regimen resulted in acceptable pregnancy rates to fixed-time AI. In a single experiment, EB, GnRH or pLH in CIDR-B- or MGA-treated beef heifers effectively synchronized ovulation for fixed-time AI. Pregnancy rates were, on average, 58.0% (range 52.5 to 65.0%). A 6- or 7-d interval from GnRH to PGF in a Cosynch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Cosynch or Ovsynch regimen improved pregnancy rates in heifers but not in cows. Synchronization of follicular wave emergence and ovulation in a two-dose PGF-based protocol resulted in acceptable fertility to fixed-time AI; the administration of EB induced luteal regression in some animals but E-17β did not. In conclusion, synchronization programs including GnRH, pLH or estradiol to synchronize follicular wave emergence and ovulation in CIDR-B-, MGA- or two-dose PGF-protocols resulted in acceptable pregnancy rates to fixed-time AI.