Timing of Preovulatory Endocrine Events, Estrus and Ovulation in Brahman × 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.

Pregnancy Rate is Greater When the Corpus Luteum is Present during the Period of Progestin Treatment to Synchronize Time of Estrus in Cows and Heifers1

“…The earlier onset of behavioral estrus after norgestomet removal in females in the PG 7 group as compared to those in the PG 17 group probably occurred as a result of the more advanced stage of the ovarian follicles in females in the PG 7 group at the time of treatment removal [22]. Earlier reports indicate that estrus occurs within 48 h of norgestomet withdrawal [5]. We have previously reported that the preovulatory surge of LH occurs earlier subsequent to norgestomet withdrawal than in cows that have had their CL lysed with PGF 2 [8].…”

“…It has been suggested that lowered pregnancy rates after treatment with norgestomet may be due to an improper temporal relationship among estrus, the preovulatory surge of LH, and ovulation [4]. In another study, delayed selection and/or maturation of the ovulatory follicle were implicated as factors involved in reduced fertility when norgestomet was used to synchronize estrus in cows [5]. In addition, reduced fertility in cows in which time of estrus is synchronized with norgestomet may result from aberrant uterine function [6].…”

Changes in ovarian follicular dynamics and luteinizing hormone profiles following different progestagen treatments in cattle

“…Wiltbank and Gonzalez Fadilla (1975), Short et al (1976) and Humphrey et al (1977) used single Norgestomet implant in combination with estradiol valerate to control estrous-cycle length. The incidence of synchrony of estrus following the above treaftnent is high (Miksch et al 198;Spitzer et al 1978 (Rentfrow et al 1987;Mikeska and Williams 1988). In a recent study (Taylor et al 1993), based on a small number of observations, we showed that prolonged maintenance of the dominant follicle with single Norgestomet implant is not detrimental to conception rate.…”

Exposure to Estrogen Mimicking the Level of Late Pregnancy Suppresses Estrus Subsequently Induced by Estrogen at the Level of the Follicular Phase in Ovariectomized Shiba Goats

“…An LH surge was defined as an increase in LH concentrations over the level of the baseline plus at least two times the SD that subsequently remained elevated in at least two consecutive samples collected at 3 h intervals [25]. The baseline was obtained as the mean concentration of the samples collected for 48 h before administration of Dose-2 E 2 B.…”