Search

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., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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 F 2α (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 × 10 6 cells) or sex-sorted (4 × 10 6 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%)., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., (Copyright © 2020 Elsevier B.V. All rights reserved.)