Effects of hCG administration on corpus luteum development and plasma sex steroid hormone concentration in beef heifers differ according to the locational relationships of the original corpus luteum and the first-wave dominant follicle

Human Chorionic Gonadotrophin (hCG) induces changes in IFN-pathway and Interferon-Stimulated Genes (ISGs) on the bovine endometrium at Day 18 of pregnancy

We hypothesized that the hCG modulates the expression of IFNT-pathway and ISGs in bovine endometrium during early pregnancy. The aim of the current study is to evaluate the effect of hCG on IFNT-pathway signals and ISGs expression in endometrial cells. For this, 29 non-lactating cross-bread cows were used in the study and submitted to a 9-day fixed-time artificial insemination (FTAI) protocol. The day of the AI was considered Day 0 (D0), and five days (D5) after the FTAI, the cows were allocated into two groups: Control and hCG group, when a hCG group received a single dose of 2.500UI of hCG. On day 18 after FTAI (D18) cows were slaughtered and endometrial tissue samples were collected. There was no difference between the embryo recovery rate of the cows in C compared to the hCG. The hCG group increased the accessory corpus luteum formation rate. The hCG resulted in greater serum progesterone concentration in the hCG group compared to the C on Day 14. Only the expression of IFNAR2 and STAT1 were upregulated on pregnant cows of the hCG group compared to the C group. The pathway genes (JAK1, STAT2, and IRF9) were not regulated. The mRNA abundance of ISG15, MX1, MX2, and OAS1 was upregulated in pregnant cows for hCG group, compared to C group. The results show that the administration of hCG, 5 days after AI, in addition to increasing the serum progesterone, modulates the expression of IFNT-pathway and ISGs on bovine endometrium on Day 18 of pregnancy.

Effects of human chorionic gonadotropin on the last day of a 5-day CIDR Synch protocol and 5 days later on circulating progesterone concentrations and luteal area in Holstein heifers

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The hCG on the last day of a 5-day CIDR Synch (day 0) enhanced original CL area on day 5.

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The hCG versus GnRH on day 0 increased serum P4 on day 5, 7, and 12.

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The hCG on day 5 induced accessory CL formation and increased serum P4 on day 7 and 12.

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The hCG on day 5 augmented original CL area on day 12 compared with no hCG on day 5.

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The hCG on day 0 and 5 (HH) increased serum P4 on day 7 compared with the other treatments.

The objective was to determine the effect of replacing GnRH with human chorionic gonadotropin (hCG) on the last day of a 5-d CIDR Synch protocol (d 0) and inducing accessory corpus luteum (CL) formation with hCG 5 d later (d 5) on serum progesterone (P4) concentrations and luteal dynamics in dairy heifers. Holstein heifers (n = 207) were synchronized with a 5-d controlled internal drug release (CIDR) Synch protocol (d −8: used CIDR inserted; d −3: CIDR removed and PGF_2α). Heifers were randomly assigned to 1 of 4 treatments on d 0: control (G; n = 55), H (n = 50), GH (n = 53), and HH (n = 49). Heifers in G were treated with 100 μg of GnRH on d 0, while H heifers received hCG (3,300 IU) on d 0. Heifers enrolled in GH were treated with GnRH on d 0 and hCG on d 5, while HH received hCG on d 0 and 5. Ovaries were scanned by ultrasound on d 0, 5, and 12, and blood was collected on d 0, 5, 7, and 12. Heifers that ovulated before or after the hCG or GnRH d 0 treatment and had P4 ≤ 0.50 ng/mL on d 0 were considered as synchronized. Overall protocol synchronization response was 93.8%, with no differences among treatments. Only synchronized heifers (n = 193) were included in the analyses of luteal dynamics after d 0. Serum P4 concentration and original CL luteal area on d 5 in heifers treated with hCG on d 0 (H + HH) were greater than in heifers treated with GnRH on d 0 (G + GH). Almost all heifers treated with hCG on d 5 had ≥2 CL on d 12 (98.6%). Ovulatory response for d 5 hCG treatment did not differ for GH versus HH (97.2 vs. 94.7%). Heifers in HH had the highest serum P4 on d 7, and G had the lowest serum P4 on d 7 and 12. In contrast, serum P4 on d 7 did not differ for H versus GH. On d 12, serum P4 and total luteal area were not different for GH versus HH. In summary, heifers that received hCG on d 0 had a larger total luteal area and greater serum P4 concentration on d 5 than heifers treated with GnRH on d 0. Moreover, hCG on d 5 promoted a greater proportion of heifers with ≥2 CL on d 12 and a larger luteal area of the original CL, which resulted in a larger total luteal area on d 12. The HH treatment successfully increased serum P4 concentrations in heifers on d 7 compared with the other treatments.

Effects of the formation and regression of accessory corpus lutea during pregnancy on plasma progesterone concentration and pregnancy status in cross-bred beef heifers

There was examination of effects of accessory corpus lutea (CLs) formation and regression during pregnancy on circulating progesterone (P₄) concentrations and pregnancy maintenance in beef heifers. Heifers (Experiment 1, n = 75; Experiment 2, n = 496) were randomly assigned to either a human chorionic gonadotropin (hCG) treatment or untreated group 5 days post-estrus, followed by embryo transfer (ET) on Days 6-8 (Day 0 = Estrus). In Experiment 1, blood samples were collected from pregnant heifers on Days 33, 40, and 47 for conducting P₄ assays. Plasma P₄ concentrations were greater in hCG-treated heifers than in untreated heifers on Day 33. In hCG-treated heifers with accessory CL regression between Days 33 and 47, plasma P₄ decreased to concentrations similar to those of untreated heifers after Day 40. In hCG-treated pregnant heifers in Experiment 2, CL regression by Day 50 of gestation was more frequent when CLs were contralateral (49.3 %) rather than ipsilateral (4.4 %, P < 0.001) to the original CL. The hCG treatment resulted in a greater pregnancy percentages on Days 30 (80.5 % and 68.6 %, P = 0.002) and 50 (76.2 % and 65.3 %, P = 0.007) compared with untreated heifers. There, however, were no differences in either pregnancy percentages on Days 30 and 50 or pregnancy losses between hCG-treated heifers with ipsilateral and contralateral accessory CLs. These results indicate accessory CL formation improves pregnancy percentages resulting from ET. Furthermore, plasma P₄ decreases associated with accessory CL regression does not affect pregnancy loss in beef heifers.