title: Timing of preovulatory endocrine events, estrus and ovulation in Brahman x Hereford females synchronized with norgestomet and estradiol valerate.
abstract: The purpose of these studies was to investigate the pattern and timing of preovulatory endocrine events, estrus and ovulation in Brahman X Hereford (F1) heifers synchronized with norgestomet and estradiol valerate. In Exp. 1, 66 nulliparous and 191 primiparous Brahman X Hereford (F1) heifers were used to estimate the interval from norgestomet implant removal to onset of estrus. The mean interval from implant removal to onset of estrus was 29.8 +/- .5 h, with 80.9% exhibiting estrus within 48 h. Endocrine and reproductive characteristics were examined in detail during Exp. 2 with 37 primiparous heifers. Continuous observation for estrus, 6-h or 2-h blood sampling and ovarian palpation per rectum were employed. All animals were artificially inseminated 48 h after implant removal. Mean interval from implant removal to onset of estrus and to onset of the luteinizing hormone (LH) surge were closely related (r = .91; P less than .0001). Mean intervals from implant removal to ovulation, onset of estrus to ovulation and onset of LH surge to ovulation were 59.1 +/- 2.5 h, 23.3 +/- 1.4 h and 23.1 +/- 1.6 h, respectively. Approximately 73% of heifers exhibited estrus within 54 h after implant removal (optimal timing); conception rate was 59.3% in this subgroup. Conception rate of heifers that did not exhibit estrus within 54 h after implant removal or exhibited an LH surge later than 12 h after estrus (delayed timing) was 10%. Assessment of plasma estradiol-17 beta concentrations suggested that retarded selection and(or) maturation of the preovulatory follicle following implant removal delayed estrus and lowered conception in up to 28% of females timed-inseminated at 48 h.
authors.affiliation: Beef Cattle Reproduction Lab. Texas Agricultural Experiment Station, Beeville 78102.
authors.forename: J C
authors.initials: JC
authors.lastname: Mikeska
authors.forename: G L
authors.initials: GL
authors.lastname: Williams
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003433:Crosses, Genetic; D004343:Drug Implants; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004966:Estrogens, Conjugated (USP) / Q000494:pharmacology*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism; D010060:Ovulation / Q000187:drug effects*; D011282:Pregnenediones / Q000008:administration & dosage / Q000494:pharmacology*; D045167:Progesterone Congeners / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D004343:Drug Implants; D004966:Estrogens, Conjugated (USP); D011282:Pregnenediones; D045167:Progesterone Congeners; C100284:norgestomet; D004958:Estradiol; D007986:Luteinizing Hormone