Implications of disparate uterine and ovarian development observed among heifers evaluated during the peripubertal period.

The incidence and implications of disparate ovarian and uterine development during the peripubertal period were evaluated in two experiments. In Experiment 1, two consecutive pre-breeding evaluations were performed on 469 heifers. In Experiment 2, data from 22,174 heifers were retrospectively analyzed. For heifers in both experiments, ovarian and uterine maturity were independently assessed via transrectal evaluation, and a two-digit reproductive tract score (RTS: first digit = ovarian; second digit = uterine) was assigned. Measures of the physical maturity of heifers were recorded at the time of pre-breeding evaluation. Heifers were subjected to 14-day progestin-based protocols for synchronization of estrus, and artificial insemination (AI) was performed. Pregnancy diagnosis was performed via transrectal ultrasonography. Incidence of disparate ovarian and uterine score was 33.7 % (158/469) in Experiment 1 % and 16.3 % (3622/22,174) in Experiment 2. Observations of disparate ovarian and uterine maturity were correlated with physical maturity. Heifers with RTS < 3-3 demonstrated poor reproductive performance, as lesser proportions of these animals conceived to the first AI service in Experiment 2 (P < 0.01) or throughout the breeding season in Experiment 1 (P = 0.03). Conception did not differ between heifers assigned congruent or disparate scores of greater than RTS = 3-3. Disparities in ovarian and uterine development are likely observed as the result of rapid, yet asynchronous growth of reproductive tissues during the peripubertal period and are not indicative of inherently reduced potential for fertility. Independent assessment of ovarian and uterine maturity may increase precision in characterizing physiologic maturity of mixed groups of prepubertal, peripubertal, and pubertal heifers.

Evaluation of the 7 & 7 Synch and 7-day CO-Synch + CIDR treatment regimens for control of the estrous cycle among beef cows prior to fixed-time artificial insemination with conventional or sex-sorted semen.

An experiment was conducted to compare the 7 & 7 Synch and 7-day CO-Synch + controlled internal drug release (CIDR®) treatment regimens before fixed-time artificial insemination (FTAI) of beef cows with conventional or sex-sorted semen. Cows (n = 1538) were blocked based on age and days postpartum (DPP) and randomly assigned to treatment regimen and semen type. Cows assigned to the 7-day CO-Synch + CIDR treatment regimen (n = 769) were administered gonadotropin-releasing hormone (GnRH) and an intravaginal progesterone-releasing insert (CIDR) on Day - 10, and administration of prostaglandin F2α (PG) coincident with CIDR removal on Day - 3. Cows assigned to 7 & 7 Synch (n = 769) were administered PG and a CIDR device on Day - 17, GnRH on Day - 10, and PG coincident with CIDR removal on Day - 3. Cows were administered GnRH coincident with FTAI, which was performed 66 h after CIDR removal with conventional (20 × 106 cells) or sex-sorted (4 × 106 cells) semen. Expression of estrus was affected by treatment regimen (P = 0.01) and by treatment regimen × DPP (P = 0.0004), as a result of imposing the 7 & 7 Synch regimen; therefore, a greater percentage of cows expressed estrus (82% compared with 64%), particularly among cows with greater DPP. Pregnancy percentages resulting from FTAI were less (P < 0.0001) when using sex-sorted semen but greater among cows treated with 7 & 7 Synch (conventional semen: 72%; sex-sorted semen: 52%) compared with 7-day CO-Synch + CIDR (conventional semen: 61%; sex-sorted semen: 44%).

Evaluation of later timepoints for split-time artificial insemination when using sex-sorted semen among beef heifers following the 14-d CIDR®-PG protocol.

An experiment was designed to evaluate later timepoints for Split-Time AI (STAI), with the hypothesis that delaying AI may improve estrous response and pregnancy per AI when using sex-sorted semen. Timing of estrus was synchronized among 794 heifers using the 14-d CIDR®-PG protocol (1.38 g progesterone intravaginal insert from Day 0-14, followed by 25 mg dinoprost tromethamine on Day 30) with STAI performed based on estrous status. Heifers were blocked based on breed, source, sire, reproductive tract score (RTS), and BW and assigned within block to one of two approaches. In Approach 66, heifers that were estrual by 66 h after PG administration were inseminated at 66 h, and remaining heifers were inseminated 24 h later (90 h). In Approach 72, heifers that were estrual by 72 h were inseminated at 72 h, and remaining heifers were inseminated 24 h later (96 h). With both approaches, heifers that were non-estrual by the final timepoint were administered 100 µg gonadorelin acetate (GnRH). Within approach, heifers were pre-assigned to receive SexedULTRA 4M™ sex-sorted or conventional semen. The proportion of heifers estrual by the first timepoint was greater (P < 0.0001) with Approach 72 (76 %; 302/395) compared to Approach 66 (61 %; 242/399). The proportion of heifers pregnant as a result of AI differed (P = 0.0005) by semen type (59 % [240/404] for conventional compared with 48 % [187/390] for sex-sorted) but was not affected by approach or approach × semen type. In summary, pregnancy per AI of heifers receiving sex-sorted or conventional semen following the 14-d CIDR®-PG protocol did not differ when STAI was delayed 6 h. The proportion of estrual heifers prior to the first timepoint, however, was greater with later STAI.

Comparison of the 7 & 7 Synch protocol and the 7-day CO-Synch + CIDR protocol among recipient beef cows in an embryo transfer program.

An experiment was designed to evaluate the effectiveness of the recently developed 7 & 7 Synch protocol to synchronize estrus among recipients prior to embryo transfer (ET). Postpartum beef cows (n = 1358) across thirteen locations were assigned to either the 7-d CO-Synch + CIDR protocol or the 7 & 7 Synch protocol prior to ET. Cows were preassigned to balanced treatments within location based on age and days postpartum, with body condition score recorded at ET. Cows assigned to the 7-d CO-Synch + CIDR protocol were administered gonadotropin-releasing hormone (GnRH; 100 µg gonadorelin acetate) on Day 7, an intravaginal controlled internal drug release (CIDR; 1.38 g progesterone) from Day 7 to Day 14, and prostaglandin F2α (PGF2α; 25 mg dinoprost tromethamine) coincident with CIDR removal on Day 14. Cows assigned to the 7 & 7 Synch protocol were administered PGF2α (25 mg dinoprost tromethamine) coincident with CIDR insertion on Day 0, GnRH (100 µg gonadorelin acetate) on Day 7, and PGF2α (25 mg dinoprost tromethamine) coincident with CIDR removal on Day 14. Cows were observed for visible signs of estrus, with GnRH (100 µg gonadorelin acetate) administered to cows failing to express estrus during the detection period. Embryo transfer was performed approximately seven days after estrus or GnRH administration. Presence of corpora lutea (CL) was determined via transrectal palpation by a single veterinarian blinded to treatment, and embryos were transferred only to cows with palpable CL. Embryo transfer was performed using either fresh or frozen embryos, with embryo stage and grade recorded for each recipient. The proportion of cows expressing estrus was increased (P < 0.0001) among cows assigned to the 7 & 7 Synch protocol (86% [529/615] vs 76% [488/640]). The proportion of cows expressing estrus and presenting with palpable CL at ET was greater (P < 0.0001) among cows following treatment with the 7 & 7 Synch protocol compared to the 7-d CO-Synch + CIDR protocol (76% [466/615] vs 65% [418/640]). Consequently, the proportion pregnant to ET was greater (P < 0.03) following the 7 & 7 Synch protocol (40% [263/653]) compared to the 7-d CO-Synch + CIDR protocol (34% [228/664]). In summary, the 7 & 7 Synch protocol involving administration of PGF2α and treatment with a CIDR for 7 days prior to GnRH improved the likelihood of estrus expression in recipients, increased the proportion of cows eligible to receive an embryo, which resulted in a greater pregnancy rate to ET.

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.

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.