Treatment with prostaglandin F2α and an intravaginal progesterone insert promotes follicular maturity in advance of gonadotropin-releasing hormone among postpartum beef cows.

An experiment was designed to evaluate treatments to promote ovarian follicular maturity in advance of administration of exogenous gonadotropin-releasing hormone (GnRH; 100 µg gonadorelin) for control of the bovine estrous cycle. We hypothesized prostaglandin F2α (PGF2α; 500 µg cloprostenol) followed by an intravaginal progesterone-releasing insert (CIDR; 1.38 g progesterone) would induce greater follicle size and serum estradiol at the time of GnRH administration. Postpartum cows (n = 194) in two locations were assigned to one of five treatments based on age, days postpartum, and body condition score. Cows in Treatment 1 were treated with the standard 7-d CO-Synch + CIDR protocol: administration of GnRH and CIDR insertion on Day -10, and administration of PGF2α and CIDR removal on Day -3. Treatments 2-5 were designed in a 2 × 2 factorial arrangement, with Treatment 1 included as an additional reference. On Day -17, cows in Treatments 2-5 received a CIDR insert, either with (Treatments 2 and 3) or without (Treatments 4 and 5) administration of PGF2α at CIDR insertion. On Day -10, all cows were administered GnRH, and CIDR inserts were either removed (Treatments 2 and 4) or remained in place until Day -3 (Treatments 3 and 5). Treatment with PGF2α and CIDR in advance of GnRH (Treatments 2 and 3) resulted in increased diameter of the largest ovarian follicle (P < 0.001) and increased serum concentrations of estradiol (P < 0.0005) on Day -10. In addition, variation among cows in CL status (no CL vs. a single CL vs. multiple CL) on Day -3 tended to be decreased (P = 0.08), with cows more likely to have a single CL rather than no CL or multiple CL. Lastly, the proportion of cows expressing estrus prior to fixed-time artificial insemination tended (P = 0.08) to be improved. Results support the hypothesis that administration of PGF2α and treatment with a CIDR for 7 days prior to GnRH promotes follicular maturity in advance of GnRH administration and may provide an approach by which to enhance response of postpartum beef cows to GnRH-based estrus synchronization programs.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers.

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F2α (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278. Fertile bulls were placed in pastures with heifers of the three NS treatment groups for a 65-day period which began 10 days after progestin treatments (MGA or CIDR) ended. Heifers in FTAI treatment groups were administered PG (25 mg, IM) 16 days after CIDR removal or 19 days following MGA withdrawal, respectively, and FTAI was performed at 66 (CIDR-PG) or 72 h (MGA-PG) after PG. Gonadotropin-releasing hormone (GnRH; 100 µg, i.m.) was administered at FTAI. Pregnancy status was determined at the end of a 65-day breeding period. Pregnancy rates on Days 21 and 65 of the breeding period differed among treatment groups based on pre-treatment pubertal status (P ≤ 0.02) and body weight (P ≤ 0.05) but did not differ by group. These data highlight the need for continued research efforts to improve reproductive management of Bos indicus-influenced females.

Altering duration of the presynchronization period in a long-term progestin-based estrus synchronization protocol for timed artificial insemination of beef heifers.

An experiment was designed to evaluate the effect of extending duration of the presynchronization treatment in a long-term progestin-based estrus synchronization protocol. Heifers were assigned to either an 18 d (Day 0-18) or 14 d (Day 4 to Day 18) CIDR® treatment (1.38 g progesterone controlled internal drug release insert; Zoetis, Madison, NJ), with prostaglandin F2α (PG; 250 µg im cloprostenol sodium) administered 16 d after CIDR® removal (Day 34). Heifers at two locations (location one, n = 193; location two, n = 649) were assigned to treatment based on reproductive tract score (RTS; Scale 1-5) and body weight. Heifers that were assigned RTS 1 were not retained for the trial (n = 6). Estrus detection aids (Estrotect®) were applied at PG. Split-time artificial insemination (STAI) was utilized and AI performed based on expression of estrus at 66 h. Expression of estrus was defined as removal of ≥50% of the grey coating from the Estrotect® patch. Heifers that expressed estrus at 66 h were inseminated then and heifers that had not expressed estrus were inseminated at 90 h. Only heifers that failed to express estrus by 90 h received gonadotropin-releasing hormone (GnRH; 100 µg im gonadorelin acetate) at the time of AI. At location one, blood samples were collected at PG and AI (66 h or 90 h) from all heifers to determine E2 concentration by radioimmunoassay, and transrectal ovarian ultrasound was performed to detail ovarian structures on a subset of heifers (n = 73) at both time points. The proportion of heifers expressing estrus did not differ between treatments, either by 66 h (60%) or in total by 90 h (84%) after PG. Pregnancy rate to STAI did not differ between treatments (P = 0.3; 52%, 14-d CIDR®-PG; 50%, 18-d CIDR®-PG), or at the end of the 60 d breeding season (P = 0.2; 86%, 14-d CIDR®-PG; 82%, 18-d CIDR®-PG). No differences were detected in mean diameter of the dominant follicle at PG (P = 0.6; 10.9 ±â€¯0.4 mm, 14-d CIDR®-PG; 11.0 ±â€¯0.4 mm, 18-d CIDR®-PG) or at STAI (P = 0.3; 12.6 ±â€¯0.4 mm, 14-d CIDR®-PG; 13.2 ±â€¯0.4 mm, 18-d CIDR®-PG), nor were any differences observed between treatments in concentrations of E2 at PG (P = 0.8; 1.1 ±â€¯0.19 pg/ml, 14-d CIDR®-PG; 1.1 ±â€¯0.19 pg/ml, 18-d CIDR®-PG) or STAI (P = 0.6; 3.8 ±â€¯0.19 pg/ml, 14-d CIDR®-PG; 3.6 ±â€¯0.19 pg/ml, 18-d CIDR®-PG). These data indicate that duration of CIDR® treatment can be extended from 14 to 18 d, thus providing flexibility in scheduling without compromising reproductive outcomes.

Evaluation of split-time artificial insemination following administration of a long or short-term progestin-based estrus synchronization protocol in beef heifers.

Fixed-time and split-time AI were compared following the melengestrol acetate (MGA®) prostaglandin F2α (Experiment 1) and 7-d CO-Synch + controlled internal drug release (CIDR®) protocols (Experiment 2). Heifers in Experiments 1 (n = 524) and 2 (n = 456) were assigned within pen to balanced treatments based on weight and reproductive tract score (RTS; Scale 1-5). In Experiment 1, MGA® (0.5 mg∙animal-1∙d-1) was fed for 14 d, and prostaglandin F2α (PG; 250 µg im cloprostenol sodium) was administered 19 d after MGA® withdrawal. In Experiment 2, gonadotropin-releasing hormone (GnRH; 100 µg gonadorelin acetate) was administered coincident with CIDR® (1.38 g progesterone [P4]) insertion. Inserts were removed after 7 d, and PG (250 µg im cloprostenol sodium) was administered at CIDR® removal. In both experiments, estrus detection aids (Estrotect®) were applied at the time of PG administration. Estrous status was recorded at FTAI or STAI. Estrus was defined as removal of ≥ 50% of the grey coating from the Estrotect® patch. Heifers assigned to FTAI treatments received GnRH and were artificially inseminated at the standard time for FTAI for each protocol: 72 or 54 h after PG administration for the MGA-PG or 7-d CO-Synch + CIDR® protocol, respectively. In the STAI treatments, only heifers that expressed estrus prior to the standard time of FTAI were artificially inseminated at that time. For heifers failing to express estrus, AI was postponed 24 h. Only heifers that failed to exhibit estrus by the delayed time received GnRH concurrent with AI. In both experiments, estrous response prior to the standard time of FTAI did not differ between treatments. Total estrous response was increased (P < 0.01) among heifers assigned to STAI in Experiment 1 (88%, STAI; 72%, FTAI) and 2 (74%, STAI; 47%, FTAI). In Experiment 1, pregnancy rates resulting from AI were greater (P < 0.04) for heifers assigned to STAI compared with FTAI (55% vs 46%, respectively). In Experiment 2, pregnancy rates resulting from AI were similar between treatments (48% and 46%, respectively; P = 0.6). In summary, when compared with FTAI, STAI resulted in greater estrous response following both the MGA®-PG and 7-d CO-Synch + CIDR® protocols. The increased estrous response through use of STAI was associated with a corresponding increase in pregnancy rates to AI following the MGA®-PG protocol; however, a similar improvement in pregnancy rates was not observed following the 7-d CO-Synch + CIDR® protocol.

Evaluation of SexedULTRA 4M™ sex-sorted semen in timed artificial insemination programs for mature beef cows.

An experiment was designed to compare fertility of SexedULTRA 4M™ sex-sorted semen and conventional, non-sex-sorted semen following either fixed-time artificial insemination (FTAI) or split-time artificial insemination (STAI) of mature suckled beef cows. Units of sex-sorted and conventional semen were produced using contemporaneous ejaculates from three commercially available sires. Units of conventional semen were generated with 25.0 × 106 live cells per 0.25 ml straw prior to freezing, and units of sex-sorted semen were generated using the SexedULTRATM Genesis III sorting technology with 4.0 × 106 live cells per 0.25 ml straw prior to freezing. Sex-sorted units were sorted to contain X chromosome-bearing sperm cells at an accuracy level of >90%. Cows (n = 1620) across four herds were treated with the 7-d CO-Synch + CIDR protocol [administration of gonadotropin-releasing hormone (GnRH) and insertion of a progesterone insert (CIDR) on Day -10, followed by administration of prostaglandin F2α (PG) and removal of CIDR inserts on Day -3]. Cows were preassigned based on age, body condition score, and days postpartum to one of the following four treatments: FTAI with SexedULTRA 4M™ sex-sorted semen, FTAI with conventional semen, STAI with SexedULTRA 4M™ sex-sorted semen, or STAI with conventional semen. On Day -3, estrus detection aids (Estrotect®) were applied. For cows in FTAI treatments, AI was performed on Day 0 at 66 h after PG administration and CIDR removal, and 100 µg GnRH was administered concurrent with AI. For cows in STAI treatments, AI was performed on either Day 0 or 1, at 66 or 90 h after PG administration and CIDR removal, based on timing of estrus expression. On Day 1 at 90 h after PG administration and CIDR removal, 100 µg GnRH was administered concurrent with AI to any STAI-treated cows that had failed to express estrus. Pregnancy rates to AI were affected (P = 0.04) by the interaction of bull and semen type. Greater pregnancy rates were obtained with conventional semen versus SexedULTRA 4M™ sex-sorted semen when using semen from Bull A (64% [176/277] versus 36% [100/278]; P < 0.0001) and Bull B (72% [200/277] versus 57% [156/276]; P < 0.01), whereas pregnancy rates to AI did not differ between conventional and SexedULTRA 4M™ sex-sorted semen when using semen from Bull C (58% [149/258] versus 52% [131/254]). Pregnancy rates did not differ significantly between cows inseminated using a STAI versus FTAI approach, regardless of whether insemination was performed with conventional semen (65% [265/409] versus 65% [260/403] or SexedULTRA 4M™ sex-sorted semen (50% [200/403] versus 48% [187/405]). However, due to the additional 24 h for potential estrus expression when performing STAI, total estrous response prior to AI was greater (P < 0.001) among cows receiving STAI (84%; 686/812) compared to FTAI (72%; 585/808), and greater pregnancy rates (P < 0.0001) were obtained among cows that expressed estrus prior to AI. In summary, the relative fertility of SexedULTRA 4M™ sex-sorted semen and conventional semen varied across bulls. Although overall pregnancy rates to timed AI did not differ between STAI and FTAI approaches, use of a STAI approach allowed for greater total estrous response prior to AI. Therefore, to achieve acceptable conception rates per unit and service the maximum number of cows with sex-sorted semen, one viable approach may be to use STAI to maximize total estrous response and restrict use of SexedULTRA 4M™ sex-sorted to only those cows expressing estrus.

The 9-d CIDR-PG protocol II: Characterization of endocrine parameters, ovarian dynamics, and pregnancy rates to fixed-time AI following use of long-term CIDR-based estrus synchronization among mature beef cows.

An experiment was designed to evaluate endocrine parameters, ovarian dynamics, and pregnancy rates to fixed-time artificial insemination (FTAI) following the 9-d CIDR-PG protocol in comparison to the 14-d CIDR-PG protocol. While both are long-term protocols using CIDR treatment for presynchronization, the 9-d CIDR-PG protocol differs from the 14-d CIDR-PG protocol in that prostaglandin F2α (PG) is administered at CIDR insertion and removal to facilitate a decreased length of progestin treatment and potentially enhance response to the presynchronization treatment. Estrus was synchronized for 393 mature beef cows across five locations. Treatments were represented in each location, and cows within each location were randomly assigned to one of the two protocols based on age, days postpartum (DPP), and body condition score (BCS). Cows assigned to the 14-d CIDR-PG treatment received a CIDR insert (1.38 g progesterone) on Day 0 with removal of CIDR on Day 14, and 25 mg PG 16 d after CIDR removal on Day 30. Cows assigned the 9-d CIDR-PG treatment received 25 mg PG and a CIDR insert (1.38 g progesterone) on Day 5; 25 mg PG and removal of CIDR on Day 14; and 25 mg PG 16 d after CIDR removal on Day 30. In both treatments, cows received FTAI on Day 33, 72 h after PG. All cows were administered 100 µg gonadotropin-releasing hormone (GnRH) concurrent with insemination. For a subset of animals in each treatment, ovarian ultrasound was performed and blood samples were collected for determination of serum estradiol concentrations at CIDR removal, PG administration, and FTAI. Protocols were compared on the basis of estrous response and pregnancy rate resulting from FTAI. Serum estradiol concentrations, follicle size, and estrous response did not differ based on treatment. However, cows assigned to the 9-d CIDR-PG protocol tended to achieve greater FTAI pregnancy rates than cows assigned to the 14-d CIDR-PG protocol (62% versus 52%; P = 0.07). Across treatments, greater pregnancy rates tended (P = 0.10) to be achieved by cows that expressed estrus prior to FTAI (69% for 9-d CIDR-PG, 58% for 14-d CIDR-PG) than by cows that failed to express estrus (55% for 9-d CIDR-PG, 47% for 14-d CIDR-PG). In summary, the 9-d CIDR-PG protocol is an effective protocol for synchronization of estrus among mature beef cows, and pregnancy rates to FTAI tended to be improved through use of the 9-d CIDR-PG compared to the 14-d CIDR-PG protocol.

Effective use of SexedULTRA™ sex-sorted semen for timed artificial insemination of beef heifers.

An experiment was designed to evaluate the relative fertility of SexedULTRATM sex-sorted semen compared to conventional, non-sex-sorted semen when used among beef heifers in conjunction with split-time AI following the 14-d CIDR-PG protocol. Units of conventional semen were generated with 25.0 × 106 live cells per 0.5 ml straw prior to freezing, and units of sex-sorted semen were generated using the SexedULTRATM Genesis III sorting technology with 4.0 × 106 live cells per 0.25 ml straw prior to freezing. Sex-sorted units were sorted to contain X chromosome-bearing sperm cells at an accuracy level of >90%. Estrus was synchronized in 851 heifers at four locations using the 14-d CIDR-PG protocol: controlled internal drug release (CIDR) insert (1.38 g progesterone) on Day 0, CIDR removal on Day 14, and administration of prostaglandin F2α (PG; 25 mg im) on Day 30. Estrus detection aids were applied at PG on Day 30 to evaluate estrous response rate, and split-time AI was performed based on estrous response. At 66 h after PG (Day 33), heifers having expressed estrus received timed AI. Heifers failing to express estrus by 66 h received timed AI 24 h later (90 h after PGF2α on Day 34). Heifers failing to express estrus by 90 h were administered gonadotropin-releasing hormone (GnRH; 100 µg im) concurrent with AI. Heifers were preassigned to treatment (insemination with either conventional or SexedULTRATM sex-sorted semen), and treatments were balanced within each location based on source, reproductive tract score, and weight. Heifers were exposed for natural service beginning 14 d after AI for the remainder of a 60 d breeding season. Pregnancy rates to AI across locations tended to be higher (P = 0.09) for heifers inseminated with conventional semen (60%; 257/429) compared to sex-sorted semen (52%; 218/422). Higher pregnancy rates to AI (P < 0.0001) were obtained among heifers that expressed estrus prior to AI than among heifers that failed to express estrus prior to AI at 90 h. Total pregnancy rates at the end of the 60 d breeding season did not differ between heifers that received sex-sorted semen at AI (89%; 376/422) and heifers that received conventional semen at AI (89%; 382/429). In summary, the pregnancy rates observed suggest that SexedULTRATM sex-sorted semen can be used effectively for timed AI of beef heifers when split-time AI is performed following the 14-d CIDR-PG protocol.

Evaluation of the 14-d CIDR-PG and 9-d CIDR-PG protocols for synchronization of estrus in Bos indicus-influenced and Bos taurus beef heifers.

Two long-term, CIDR-based estrus synchronization protocols were evaluated among Bos indicus-influenced and Bos taurus beef heifers. Treatments were evaluated on the basis of estrous response and pregnancy rate resulting from fixed-time artificial insemination (FTAI), and these outcomes were analyzed retrospectively relative to reproductive tract score (RTS; Scale 1-5) at treatment initiation. Estrus was synchronized for 1139 heifers in three locations, and heifers were assigned to one of two treatments within each location based on RTS. Heifers assigned to the 14-d CIDR-PG protocol received a controlled internal drug release (CIDR) insert (1.38 g progesterone) on Day 0, CIDR removal on Day 14, administration of prostaglandin F2α (PG; 25 mg im) on Day 30, and administration of gonadotropin-releasing hormone (GnRH; 100 µg im) concurrent with FTAI on Day 33, 66 h after PG. Heifers assigned to the 9-d CIDR-PG protocol received administration of PG concurrent with CIDR insertion on Day 5, administration of PG concurrent with CIDR removal on Day 14, administration of PG on Day 30, and administration of GnRH concurrent with FTAI on Day 33, 66 h after PG. Estrus detection aids were applied at CIDR removal on Day 14 and at PG on Day 30 to evaluate estrous response rate. Mean RTS differed (P < 0.0001) based on biological type due to higher rates of estrous cyclicity (RTS 4 and 5) among Bos taurus heifers (72%; 416/574) than among Bos indicus-influenced heifers (27%; 150/565). The proportion of heifers expressing estrus following CIDR removal was greater (P = 0.01) among heifers assigned to the 14-d CIDR-PG treatment (88%; 492/559) compared to the 9-d CIDR-PG treatment (83%; 480/580). Estrous response following CIDR removal was also higher (P < 0.0001) among Bos taurus (95%; 547/574) compared to Bos indicus-influenced (75%; 425/565) heifers. Rate of estrous response prior to FTAI did not differ significantly based on treatment but was higher (P < 0.0001) among Bos taurus heifers (60%; 344/574) than among Bos indicus-influenced heifers (45%; 253/565). However, the effect of biological type on estrous response was not significant when RTS was included in the model, as RTS significantly (P < 0.0001) affected the rate of estrous response both at CIDR removal and prior to FTAI. Across treatments and biological types, heifers that expressed estrus prior to AI achieved higher (P < 0.0001) AI pregnancy rates than heifers failing to express estrus. Pregnancy rates to FTAI did not differ significantly based on treatment in either biological type. Higher rates of estrous cyclicity among Bos taurus heifers resulted in higher FTAI pregnancy rates among Bos taurus (51%; 290/574) compared to Bos indicus-influenced heifers (39%; 218/565). However, pregnancy rates of respective RTS did not differ based on biological type. In summary, long-term CIDR-based protocols provide a simple, effective method of estrus synchronization in Bos indicus-influenced and Bos taurus beef heifers. Moreover, these results highlight the importance of management practices that result in high rates of estrous cyclicity prior to protocol initiation, particularly among later maturing breeds and biological types.