M.L. Mussard

Decreasing the interval between GnRH and PGF2α from 7 to 5 days and lengthening proestrus increases timed-AI pregnancy rates in beef cows

Four experiments were conducted in postpartum beef cows to evaluate the influence of reducing the interval from GnRH to PGF(2alpha) from 7 to 5d in a Select-Synch + CIDR or CO-Synch + CIDR estrous synchronization program. In Expt 1, cows (n=156) were treated with either a 7 or 5d Select-Synch + CIDR program. A second PGF(2alpha) treatment was given to all cows in all experiments at 12h after the initial PGF(2alpha) (to ensure that luteolysis occurred with the 5d program). Estrous response, interval to estrus, conception rate, and first service AI pregnancy rates were similar between treatments. In Expt 2, cows (n=223) were treated with either a 7 or 5d CO-Synch + CIDR program, with timed-AI concomitant with GnRH at 60 h after PGF(2alpha). Timed-AI pregnancy rates were similar between treatments. In Expt 3 (n=223) and 4 (n=400) cows were treated with either a 7 or 5d CO-Synch + CIDR program with timed-AI concurrent with GnRH at either 60 h (7d) or 72 h (5d) after CIDR withdrawal. Timed-AI pregnancy rates were 13.3% (P<0.05; Expt 3) and 9.1% (P<0.05; Expt 4) greater for the 5 than 7d program. In conclusion, timed-AI pregnancy rates were improved with a 5d CO-Synch + CIDR program with timed-AI at 72 h after CIDR withdrawal, compared to a 7d CO-Synch + CIDR program with timed-AI at 60 h after CIDR withdrawal.

Influence of the length of proestrus on fertility and endocrine function in female cattle

Previous research from our laboratory in beef cattle suggests that ovarian follicle maturity and subsequent fertility is influenced by length of proestrus across a range of follicle sizes. To test this hypothesis an animal model was used in which ovulation from similar sized follicles was induced following either a long (LPE; approximately 2.25 days) or short (SPE; approximately 1.25 days) proestrus (interval from PGF(2alpha) administration to a GnRH-induced LH surge). Specific objectives were to compare pregnancy rates and luteal phase concentrations of progesterone (Experiment 1) and to characterize preovulatory concentrations of estradiol, the GnRH-induced LH surge, and concentrations of progesterone in the subsequent estrous cycle (Experiment 2) between the LPE and SPE treatments. In Experiment 1, ovulation from follicles that were previously synchronized using follicular aspiration was induced with GnRH (Day 0) after either 2.25 days (LPE; n=40) or 1.25 days (SPE; n=38) of proestrus. Lactating and non-lactating cows were inseminated 12h following GnRH administration. Ovulatory follicle diameter was similar between treatments. Pregnancy rates to AI were greater (P<0.01) in the LPE (50.0%) compared to the SPE (2.6%) treatment. The proportion of cows having a short luteal phase in the subsequent estrous cycle was greater (P<0.01) in the SPE than LPE treatment. In cows with a luteal phase of normal length, timed-AI pregnancy rates and concentrations of progesterone in the subsequent luteal phase were greater (P<0.05) in the LPE than SPE treatment. In Experiment 2, a similar experimental approach was taken with non-lactating beef cows and ovulation was induced following either 2.2 days (LPE; n=8) or 1.2 days (SPE; n=8) of proestrus. Ovulatory follicle diameter was similar between treatments. Concentrations of estradiol during the proestrus period were greater (P<0.05) in the LPE than SPE treatment from Days -1.9 to Day 0 (GnRH administration). Concentration of LH during the GnRH-induced LH surge and concentrations of progesterone in the subsequent estrous cycle did not differ between treatments although there was a tendency (P=0.10) for increased incidence of short luteal phases in the SPE treatment. In conclusion, decreasing the length of proestrus before induction of ovulation of a large follicle resulted in lesser pregnancy rates and an increased incidence of short luteal phases. The impact of a shortened proestrus on concentrations of progesterone in cows with luteal phases of normal length varied among experiments. Decreased circulating concentrations of estradiol during the preovulatory period and/or reduced concentrations of progesterone during the subsequent estrous cycle in cows that do not experience a shortened luteal phase may represent the mechanism responsible for reduced fertility with the SPE treatment.

Impact of preovulatory estradiol concentrations on conceptus development and uterine gene expression

This experiment was conducted to determine the effect of altering preovulatory estradiol concentrations, through manipulation of length of proestrus, on peripheral progesterone concentrations, conceptus development, interferon tau (IFNT) production and uterine gene expression in cattle. Approximately 6 days after a time-synchronized ovulation, all antral follicles (≥5 mm) were ablated from the ovaries in beef heifers. To manipulate preovulatory estradiol concentrations, the length of proestrus prior to the GnRH-induced LH surge was altered between treatments. Heifers were administered PGF(2α) either -2.5 days (2.5 days of proestrus; HiE2; n=5) or -1.5 days (1.5 days of proestrus; LoE2; n=5) prior to GnRH (Day 0 of the experiment; 6.75 days after follicle ablation). Follicular dynamics and estradiol concentrations were evaluated during proestrus and progesterone concentrations were analyzed in the subsequent estrous cycle. On Day 7, embryos were transferred into all heifers using standard procedures. On Day 15.5 heifers were slaughtered, the reproductive tract was flushed to collect the conceptus and uterine flush media, and the uterine tissue was processed for subsequent analyses. Peripheral progesterone concentrations, conceptus development and IFNT production were similar between treatments. However, amount of nuclear progesterone receptor in the deep glandular epithelium and mRNA concentrations for estradiol receptor alpha (ESR1) in the uterine endometrium were less in the LoE2 than HiE2 treatment. These changes in uterine characteristics in heifers with lower preovulatory estradiol concentrations were not related to aspects of conceptus development monitored, however, it is speculated that the alterations in mRNA and receptor protein detected may contribute to pregnancy failure subsequent to day 15.5 of gestation.

The requirement of GnRH at the beginning of the five-day CO-Synch + controlled internal drug release protocol in beef heifers.

The objective of this study was to determine if the omission of GnRH at controlled internal drug release device (CIDR) insertion would impact pregnancy rates to timed AI (TAI) in beef heifers enrolled in a 5-d CO-Synch + CIDR protocol that used 1 PGF2α dose given at CIDR removal. Yearling beef heifers in Ohio in 2 consecutive breeding seasons (2011, n = 151, and 2012, n = 143; Angus × Simmental), Utah (2012, n = 265; Angus × Hereford), Idaho (2012, n = 127; Charolais), and Wyoming (2012, n = 137; Angus) were enrolled in the 5-d CO-Synch + CIDR protocol. At CIDR insertion (d -5), heifers were randomly assigned either to receive 100 μg GnRH (GnRH+; n = 408) or not to receive GnRH (GnRH-; n = 415). At CIDR removal (d 0 of the experiment), 25 mg PGF2α was administered to all heifers. All heifers were inseminated by TAI and given 100 μg GnRH 72 h after PGF2α (d 3). In heifers at the Ohio locations (n = 294), presence of a corpus luteum (CL) at CIDR insertion (d -5) was determined via assessment of progesterone concentrations (2011) and ovarian ultrasonography (2012). Subsequently, in both years, ovarian ultrasound was conducted on d 0 to determine the presence of a new CL. In this same subgroup of heifers, blood samples for progesterone analysis were collected on d 3 to assess luteal regression. Pregnancy diagnosis was performed between 32 and 38 d after TAI. At CIDR withdrawal, presence of a new CL was greater (P < 0.05) in the GnRH+ (55.8%, 82/147) than GnRH- (26.5%, 39/147) treatment. Incidence of failed luteal regression did not differ between the GnRH+ (3.4%) and GnRH- (0.7%) treatments. Pregnancy rate to TAI did not differ between the GnRH+ (50.5%) and GnRH- (54.9%) treatments. In conclusion, although the incidence of a new CL at CIDR removal was increased in the GnRH+ treatment, omission of the initial GnRH treatment in the 5-d CO-Synch + CIDR protocol did not influence TAI pregnancy rate in yearling beef heifers. In addition, a single dose of PGF2α at CIDR removal was effective at inducing luteolysis in yearling beef heifers enrolled in the 5-d CO-Synch + CIDR protocol, regardless of whether or not the initial GnRH treatment was given.

Role of progesterone concentrations during early follicular development in beef cattle: II. Ovulatory follicle growth and pregnancy rates

Two experiments were conducted to investigate the role of relatively lesser and greater progesterone (P4) concentrations during early follicular development on ovulatory follicle growth and pregnancy rate in beef cattle. In Experiment 1, time of ovulation was synchronized with the 5 d CO-Synch + CIDR (Controlled Internal Drug Release) program in multiparous cows (n = 241). Six days after the 2nd GnRH injection of the pre-synchronization program (d 0), ablation of follicles ≥ 5 mm in the ovaries was performed and cows were assigned to receive either a previously used CIDR and 2x-25 mg PGF2α doses 8 h apart (LoP4), or a new CIDR (HiP4). On d 5, CIDR were removed from all cows, 2x-25 mg PGF2α were administered, and estrous detection tail paint was applied. Timed artificial insemination (TAI) was performed on d 8. On d 5, P4 concentrations were greater (P <  0.01) in the HiP4 (4.9 ± 0.13 ng/mL) than LoP4 (1.0 ± 0.06 ng/mL) treatment group. Conversely, d 5 estradiol (E2) concentrations and follicular diameter were greater (P <  0.01) in the LoP4 (5.0 ± 0.23 pg/mL and 8.9 ± 0.20 mm) than HiP4 (1.5 ± 0.12 pg/mL and 7.4 ± 0.15 mm) treatment group. Follicular diameter at TAI (12.0 ± 0.12 mm, Table 1) and TAI pregnancy rate did not differ (P >  0.10) between treatment groups. In Experiment 2, a new follicular wave was induced with estradiol benzoate on d -7, and cows (n = 275) were assigned on d 0 to receive 25 mg PGF2α and either have the CIDR replaced with a new CIDR (HiP4) or the used CIDR was left in place (LoP4).Furthermore, all cows received GnRH on d 0. The CIDRs were removed from all cows on d 5 and two doses of -25 mg PGF2α were administered. Estrous detection combined with AI 12 h later (Estrus-AI) was performed for 60 h after CIDR removal with TAI coupled with GnRH administration at 72 h if estrus was not detected. The concentrations of P4 on d 5 were greater (P <  0.01) in the HiP4 (2.8 ± 0.10 ng/ml) than LoP4 (1.7 ± 0.05 ng/mL) treatment group. For cows that were detected in estrus after PGF2α administration, estrous response (83.5%) and interval to estrus (55.0 ± 0.5 h) did not differ between treatment groups. Pregnancy rate (combined Estrus-AI and TAI) that resulted from breeding at the time of the synchronized time of estrus was similar between treatment groups (HiP4: 77.1%; LoP4: 82.3%). In conclusion, differences in P4 concentrations during early follicular development do not effect pregnancy rate in beef cows when the cows are inseminated at the time of a synchronized estrus if the cows have similar intervals of proestrus.

Role of progesterone concentrations during early follicular development in beef cattle: I. Characteristics of LH secretion and oocyte quality

Objective was to investigate the effect of different progesterone (P4) concentrations during early follicular development on luteinizing hormone (LH) secretion and oocyte characteristics in beef cows. Primiparous cows (n = 24) were estrous pre-synchronized and follicular ablation was performed (d 0) 6 days following the time of ovulation. At the time of follicular ablation, cows were assigned to either: 1) high P4 treatment - HiP4; a new CIDR was inserted on d 0 to supplement P4 from the existing corpus luteum [CL], or 2) low P4 treatment - LoP4; a previously-used CIDR and two doses of PGF 8 to 12 h apart were given on d 0. Concentrations of P4 were greater (P < 0.01) in the cows of the HiP4 than LoP4 group on d 1.5, 2.5, and 3.5. Peripheral concentrations of E2 were greater (P < 0.05) in the cows of the LoP4 than HiP4 group on d 2.5 and 3.5. Frequency of LH pulses was greater (P <  0.05) in the LoP4 than HiP4 group on d 2.5, but mean LH concentration and pulse amplitude did not differ between treatments. Number of follicles aspirated per cow, total oocytes recovered, recovery rate, percentage of oocytes graded 1 to 3, oocyte diameter, percentage BCB+ oocytes, and relative abundance of oocyte mRNA for FST did not differ (P >  0.10) between treatments. In conclusion, lower P4 concentrations during early follicular development resulted in increased LH pulse frequency and E2 concentrations, but did not affect characteristics of oocyte developmental competence.