Comparison of two intravaginal progesterone-releasing devices in shortened-timed artificial insemination protocols in beef cattle

Influence of repeated estrus synchronization treatment on hormone secretion, growth, and development of dairy goats

In large-scale intensive farms, dairy goats often undergo frequent estrus synchronization (ES) treatment, which may result in a decline in reproductive performance; however, the underlying mechanism remains unclear. The present study aimed to investigate the effect of pregnant mare serum gonadotropin (PMSG) and progesterone (P4)-mediated ES treatment on fertility in dairy goats, while also identifying key metabolic and endocrine mechanisms that influence reproductive performance in does subjected to repeated ES treatment. Forty-eight Saanen does were randomly assigned to two groups (24 goats each) that received ES treatments either thrice fortnightly (3-PMSG) or once (1-PMSG) simultaneously with the third ES treatment of the 3-PMSG group during the breeding season. ES treatment was performed via the intravaginal insertion of a controlled internal drug release (CIDR) device impregnated with 300 mg P4, followed by 300 IU PMSG injections 48 h before CIDR withdrawal. Blood was collected to detect the level of hormones and blood biochemical indices. Additionally, estrus rate, fecundity rate, body weight, size, and lactation performance were measured. The results showed that repeated ES treatment markedly decreased the estrus rate and fecundity rate of goats. Among the does in all groups, there was no substantial difference in follicle stimulating hormone, luteinising hormone, gonadotropin-releasing hormone, melatonin, growth hormone, PMSG, total cholesterol, total protein, and glucose levels, as well as the body weight, body size, and lactation performance. Repeated ES treatment elevated estrogen (E2) levels 36, 48, and 72 h post-CIDR removal; increased P4 upon CIDR insertion; and raised PMSG antibody levels 24, 48, and 72 h post-CIDR removal. The results suggest that elevated anti-PMSG levels are the primary reason for the decline in ES efficiency, and that high E2 and P4 levels at some time points also impair reproductive performance. These findings provide novel insights into the metabolic effects of repeated PMSG stimulation in goats, guiding future reproductive hormone use in breeding practices.

A high dose of initial GnRH increased ovulatory response and fertility in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol

The objectives of this study were to investigate the effect of presynchronization or dose of GnRH on ovulatory response to initial GnRH, estrus expression and reproductive outcomes in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Heifers were fitted with a collar-mounted automated activity monitoring system on Day -5 and were assigned randomly to one of three groups: 1) G100 (n = 111), a 5-d CO-Synch plus PRID protocol with administration of 100 μg of GnRH at the time of PRID insertion (Day 0), 500 μg of cloprostenol (PGF) at the time of PRID removal (Day 5) and again 24 h later (Day 6); 2) G200 (n = 112), same as G100 except 200 μg GnRH was administered on Day 0; 3) P10 (n = 111), PRID + PGF on Day -5 followed by a 5 d CO-Synch with administration of 100 μg of GnRH on Day 0, PGF at the time of PRID removal (Day 5) and again 24 h later (Day 6). Approximately 72 h after PRID removal (Day 8), all heifers were timed-inseminated (TAI) and concurrently 100 μg of GnRH was administered to those not exhibiting estrus. All inseminations were done by one technician using either sex-sorted (n = 265) or conventional (n = 69) frozen-thawed semen. Transrectal ultrasonography was done to determine ovarian cyclicity and normalcy of the reproductive tract, ovarian dynamics and pregnancy. All heifers were cyclic and ovulatory response to initial GnRH was greater (P < 0.01) in G200 (51.8%) and P10 (47.7%) compared to G100 (27.9%). Estrus expression rate tended to be greater (P = 0.08) in G100 (93.7%) compared to G200 (85.7%) and intermediate in P10 (89.2%). Expression of estrus was associated positively with P/AI at 45 d post-TAI (P < 0.01; 70.2 vs. 31.4% for heifers expressing or not expressing estrus). Heifers in the G200 group had greater P/AI at 30 (P < 0.01) and 45 (P = 0.01) d post-TAI (79.5 and 75.9%, respectively) compared to those in G100 (63.1 and 60.4%) or P10 (64.0 and 62.2%) groups. Pregnancy loss did not differ among treatment groups (overall 3.9%). Results indicate that increasing the dose of the initial GnRH from 100 to 200 μg resulted in increased ovulatory response and improved P/AI in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Although heifers presynchronized with a combination of PRID and PGF had an increased ovulatory response to the initial GnRH, P/AI did not differ from the standard progesterone based 5-d CO-Synch protocol.

Evaluation of Corpus Luteum and Plasma Progesterone the Day before Embryo Transfer as an Index for Recipient Selection in Dairy Cows

The aim of the present study was to evaluate the effects of synchronization method, season, parity, corpus luteum (CL) size, and progesterone (P4) levels on the pregnancy rate after bovine embryo transfer (ET). Among 165 recipient candidates who received 1 of 2s estrus synchronization treatments, 96 heifers and 43 cows were selected through rectal examination and used as recipients. The day before ET, the CL size and plasma P4 concentration were evaluated. The CL sizes and plasma P4 levels were not different between the selected and unselected candidates, and the pregnancy rates with the two synchronization methods were not different. However, the pregnancy rates were higher in heifers than in lactating cows, and also higher after ET performed from September to February than from March to August (p < 0.05). The recipients with a CL larger than 1.5 cm showed statistically higher pregnancy rates, and although there was no statistical significance, the pregnancy rate was higher when the plasma P4 levels were between 2.0 and 4.0 ng/mL. Exposure to a stressful environment and repeated manipulations can reduce the success rate of ET, and recipient selection with an optimal CL size and P4 level can increase the success rate of ET.

Enhanced progesterone support during stimulated cycles of transvaginal follicular aspiration improves bovine in vitro embryo production

The in vitro production (IVP) of cattle embryos requires that germinal-vesicle stage oocytes undergo a period of maturation in vitro prior to fertilization and culture to the blastocyst stage. Success of IVP in taurine cattle is enhanced following ovarian stimulation prior to oocyte retrieval (OPU), particularly if preceded by a short period of FSH withdrawal ('coasting'). However, evidence regarding the importance of progesterone (P4) support during OPU-IVP is equivocal. The current study, therefore, determined the effects of increased peripheral P4 concentrations during FSH-stimulated ('coasted') cycles of OPU. Progesterone support was provided by either an active corpus luteum (CL) and/or one of two intravaginal P4 releasing devices (i.e., CIDR® [1.38 g P4] or PRID® Delta [1.55 g P4]). Expt. 1 established an initial estrus prior to OPU, allowing CL formation (single luteal phase) spanning the first two of five cycles of OPU; the remaining three cycles were supported by either a CIDR® or PRID® Delta. Expt. 2 commenced with two cycles of dominant follicle removal (including prostaglandin F_2α) undertaken seven days apart prior to six cycles of OPU. The absence of a CL meant that these cycles were supported only by a CIDR® or PRID® Delta. As each experiment involved several sequential cycles of OPU, the cumulative effects of device use on vaginal discharges were also assessed. Each experiment involved 10 sexually mature Holstein heifers. In the absence of a CL, peak plasma P4 concentrations were greater (P = 0.002) for the PRID® Delta (4.3 ± 0.22) than for the CIDR® (2.9 ± 0.22). In Expt. 1 there was an interaction (P < 0.05) between CL presence at OPU and P4 device on Day 8 blastocyst yields, indicating an effect of P4 device only when the CL was absent. The percentage hatching/hatched blastocysts of matured oocytes for the CIDR® and PRID® Delta was 44.3 ± 5.04 and 41.0 ± 5.40 in the presence, and 17.1 ± 3.48 and 42.2 ± 3.76 in the absence, of a CL (P = 0.018). Combined analyses of data from Expt. 1 and 2, when no CL was present, confirmed that Day 8 blastocyst yields were greater (P = 0.022) for the PRID® Delta than the CIDR®. Vaginal discharge scores were higher (P < 0.001) for the PRID® Delta than the CIDR® in Expt. 1 but not in Expt 2; however scores were low, did not increase with repeated use, and thus were deemed of no clinical or welfare concern. In conclusion, enhanced P4 support during FSH-stimulated cycles of OPU-IVP can improve in vitro embryo development.