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 F_2α (PGF_2α; 25 mg dinoprost tromethamine) coincident with CIDR removal on Day 14. Cows assigned to the 7 & 7 Synch protocol were administered PGF_2α (25 mg dinoprost tromethamine) coincident with CIDR insertion on Day 0, GnRH (100 μg gonadorelin acetate) on Day 7, and PGF_2α (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 PGF_2α 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 F_2α (PGF_2α; 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 PGF_2α 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 PGF_2α 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 PGF_2α 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 PGF_2α 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.