Equine chorionic gonadotropin alters luteal cell morphologic features related to progesterone synthesis

The effectiveness of low-dose of eCG in timed AI Nelore (Bos indicus) heifers

This study evaluated the efficacy of the administration of different doses of equine chorionic gonadotropin (eCG; 0 IU, 200 IU, or 300 IU) at the time of the progesterone device removal in 2-year-old Nelore (Bos indicus) heifers synchronized for fixed-timed artificial insemination (FTAI). On day 0 (D0), a total of 398 heifers received 2 mg of oestradiol benzoate i.m., 0.53 mg of cloprostenol i.m., and an eight-day previously used (second use) intravaginal device containing 1 g of progesterone (P4). Eight days later (D8), simultaneous with the P4 device removal, 0.5 mg of oestradiol cypionate i.m. and 0.53 mg of cloprostenol i.m. were administered. At the same time, heifers were randomly assigned to receive one of the following treatments: G-0 IU (n = 141; no eCG treatment), G-200 IU (n = 132; treated with 200 IU of eCG), and G-300 IU (n = 125; treated with 300 IU of eCG). FTAI was performed 48 h after the P4 device removal (D10). Ultrasonographic evaluations were performed at D0, D10, and D17. Heifers were scanned to measure the size of the largest follicle (LF), the presence, number, and size of the corpus luteum (CL), and the ovulation rate. Subsequently, at D40, the heifers underwent scanning to determine the pregnancy rate and identify any twin pregnancies. Additionally, at D70, scans were performed to assess pregnancy loss (PG). Data were analysed by orthogonal contrasts [C1 (eCG effect): control x (200 IU + 300 IU) and C2 (eCG dose effect): 200 IU × 300 IU]. On D0, CL presence was similar between the groups [G-0 IU = 65.2% (92/141), G-200 IU = 55.3% (73/132), and G-300 IU = 63.2% (79/125); p = .16]. No interactions between the presence of CL on D0 and eCG treatment were found for any of the variables (p > .05). The diameter of the LF at FTAI (D10) was not influenced by eCG treatment (p = .22) or eCG dose (p = .18). However, treatment with eCG increased the diameter of the CL at D17 (G-0 IU = 15.7 ± 0.3 mmb , G-200 IU = 16.6 ± 0.2 mma , and G-300 IU = 16.6 ± 0.3 mma ; p = .001), regardless of the dose used (p = .94). The ovulation rate was higher in heifers treated with eCG [G-0 IU = 79.4%b (112/141), G-200 IU = 90.2%a (119/132), and G-300 IU = 93.6%a (117/125); p = .002], but there was no effect of eCG dose (p = .36). Pregnancy per AI (P/AI) on D40 [G-0 IU = 32.6%b (46/141), G-200 IU = 42.4%a (56/132), and G-300 IU = 42.4%a (53/125); P = 0.05] and D70 [G-0 IU = 29.1%b (41/141), G-200 IU = 40.9%a (54/132), and G-300 IU = 40.8%a (51/125); p = .02] were higher on heifers that received eCG; however, no dose effect was observed for P/AI on D40 (p = .89) nor D70 (p = .98). Pregnancy loss between D40 and D70 tended to reduce (p = .07) in eCG-treated heifers without dose effect (p = .91). Heifers with CL at D0 presented a greater follicle diameter (LF) on D10 (With CL = 11.2 ± 0.2 mm and Without CL = 10.2 ± 0.2 mm; p = .05), CL diameter on D17 (With CL = 15.8 ± 0.03 mm and Without CL = 11.8 ± 0.6 mm; p = .01), and ovulation rate [With CL = 95.5% (233/244) and Without CL = 74.7% (115/154); p = .01]. However, no difference in pregnancy rate at D40 (p = .52) and D70 (p = .84) was found. In conclusion, eCG treatment increases ovulation and pregnancy rates of heifers submitted to a FTAI protocol. Furthermore, eCG treatment increases the diameter of the CL after FTAI and reduces pregnancy losses. No dose effect was observed, suggesting Nelore (Bos indicus) heifers respond to 200 IU of eCG treatment for FTAI.

Equine chorionic gonadotropin treatment and timed artificial insemination for dairy cow production under heat stress

This study investigated the effects of timed artificial insemination (TAI) and equine chorionic gonadotropin (eCG) administration on lactating dairy cows under heat-stress conditions (average temperature-humidity index: 80). Timed artificial insemination was performed on the cows with (n = 57) or without (control, n = 41) supplementation with 500 IU of eCG at the day of PGF2α treatment using the CIDR-Ovsynch protocol. GnRH was administered, and a progesterone device (CIDR) was inserted on Day -10 of the treatment protocol. The CIDR was removed on Day -3, and the cows were treated with PGF2α. Two days later, a 2nd GnRH injection was administered. Subsequently, AI was performed on Day 0 (16-20 h after the 2nd GnRH injection), and pregnancy was diagnosed on Days 32 and 60. Plasma progesterone (P4) concentrations were measured after AI. Results showed that the eCG group had a higher pregnancy per AI (P/AI) than the control group (43.9 vs. 12.2%, P = 0.002), which was also accompanied by elevated P4 levels. Four cows in the eCG group had multiple calves, representing 7.0 and 16.0% of the group and pregnant cows, respectively. In conclusion, 500 IU of eCG combined with CIDR-Ovsynch in lactating dairy cows under severe heat stress conditions successfully improved fertility. However, the protocol may have a slight risk of multiple births.

Use of new recombinant proteins for ovarian stimulation in ruminants

Currently, gonadotropin products (follicle stimulating hormone, FSH, and luteinizing hormone, LH) used in animal reproduction are produced by extraction and purification from abattoir-derived pituitary glands. This method, relying on animal-derived materials, carries the potential risk of hormone contamination and pathogen transmission. Additionally, chorionic gonadotropins are extracted from the blood of pregnant mares (equine chorionic gonadotropin; eCG) or the urine of pregnant women (human chorionic gonadotropin; hCG). However, recent advancements have introduced recombinant gonadotropins for assisted animal reproduction therapies. The traditional use of FSH for superovulation has limitations, including labor requirements and variability in superovulation response, affecting the success of in vivo (SOV) and in vitro (OPU/IVEP) embryo production. FSH treatment for superstimulation before OPU can promote the growth of a homogenous follicular population and the recovery of competent oocytes suitable for IVEP procedures. At present, a single injection of a preparation of long-acting bovine recombinant FSH (rFSH) produced similar superovulation responses resulting in the production of good-quality in vivo and in vitro embryos. Furthermore, the treatment with eCG at FTAI protocol has demonstrated its efficacy in promoting follicular growth, ovulation, and P/AI, mainly in heifers and anestrous cows. Currently, treatment with recombinant glycoproteins with eCG-like activity (r-eCG) have shown promising results in increasing follicular growth, ovulation, and P/AI in cows submitted to P4/E2 -based protocols. Bovine somatotropin (bST) is a naturally occurring hormone found in cows. Recombinant bovine somatotropin (rbST), produced through genetic engineering techniques, has shown potential in enhancing reproductive outcomes in ruminants. Treatment with rbST has been found to improve P/IA, increase donor embryo production, and enhance P/ET in recipients. The use of recombinant hormones allows to produce non-animal-derived products, offering several advantages in assisted reproductive technologies for ruminants. This advancement opens up new possibilities for improving reproductive efficiency and success rates in the field of animal reproduction.

[Influence of an eCG administration on puerperal involution and fertility in Simmentaler cows]

SUBJECT AND AIM

In the literature, various methods aiming for a promotion of uterine involution and ovarian function in post-partum dairy cattle have been described. Recently, successful use of equine choriongonadotropin (eCG) in this context has been repeatedly reported, while other studies have failed to demonstrate positive effects of eCG administration on puerperal involution in cows. Due to the contradictory results described in the literature, the aim of this field study was to verify whether the administration of eCG on day 10 post-partum exerts a positive effect on uterine involution, ovarian activity and fertility indices in Simmental cows.

MATERIAL AND METHODS

In nine dairy farms, 205 Simmental cows were divided by lot into three groups: Group 1 animals received 500 I.U. eCG, group 2 received 50 µg gonadorelin, and group 3 animals received 250 mg butafosfan and 125 µg cyanocobalamin (control group). Treatment was administered on day 10 post-partum in each case. The animals were examined clinically and ultrasonographically on the 10th, 25th and 42nd day post-partum and the time to insemination and pregnancy were recorded. Group comparison with respect to the recorded parameters was initially performed without considering confounding factors by analysis of variance. In the second step, potential influencing variables (lactation, milk yield, change in backfat thickness, retentio secundarium and serverity of the obstetric intervention) were taken into account, as well as the combination of the random factors "farm" and "individual animal within the farm".

RESULTS

The administration of eCG exhibited no significant effect on uterine involution, however, the cervical involution was influenced significantly. In the group of cows with eCG treatment, ovarian cysts were detected significantly more frequently on day 25 post-partum (p=0.04). This difference did not persist on the 42nd day post-partum. Neither voluntary waiting period nor the days open were significantly shortened by eCG administration. Lactation number showed a significant effect on uterine involution. Heifers exhibited more rapid involution by day 42 post-partum than cows.

CONCLUSION

Administration of eCG in Simmentaler cows at day 10 post-partum showed no positive effect.

CLINICAL RELEVANCE

The use of eCG in early puerperium to promote fertility in the cow should be avoided.

"Which Factors Affect Pregnancy Until Calving and Pregnancy Loss in Buffalo Recipients of in vitro Produced Embryos?"

In vitro embryo production and embryo transfer (ET) in buffaloes has been developed for decades. However, most studies are focused on the donor or laboratory improvements, and there is a lack of reports regarding the recipients. Therefore, our aim was to investigate factors associated to pregnancy (P/ET), pregnancy loss (PL), and calving rates in buffalo recipients. The studied factors were season, recipient parity, the synchronization protocol, the CL diameter, asynchrony between the embryo and the recipient, the day of the recipient estrous cycle, the embryo (fresh vs. vitrified), the day of embryo development, and the embryo stage. These retrospective data, from a program of in vitro produced embryos, were analyzed by logistic regression, and the odds ratio was also estimated. Two factors were related to P/ET and the calving rate: (1) progesterone associated to estradiol plus eCG protocol for fixed time ET tended to affect positively P/ET on day 30 (41.9 vs. 36.1%, respectively; P = 0.07; AOR = 1.28) and P/ET on day 60 (37.8 vs. 36.1%, respectively; P = 0.09; AOR = 1.08) compared to the Ovsynch protocol; and (2) the CL diameter (≥14.5 mm) at transfer increased P/ET on day 30 (47.4 vs. 32.5%; P < 0.01; AOR = 1.87) and on day 60 (45.3 vs. 27.7%; P < 0.01; AOR = 2.16), and also the calving rate (37.9 vs. 21.7%; P < 0.01; AOR = 2.20). PL was greater when ET was done in the nonbreeding season compared to the breeding season (PL 30-60: 12.8 vs. 0.0%, P = 0.01; AOR > 999.99; PL 60-calving: 26.8 vs. 3.6%, P = 0.03; AOR = 9.90; and PL 30-calving: 36.2 vs. 3.6%, P = 0.01; AOR = 15.30). In conclusion, the data of our study indicated that the synchronization protocol, the CL diameter, and ET during the breeding season impacted the reproductive efficiency of buffalo recipients.

Size and number of corpora lutea and serum progesterone concentrations when administering two doses of eCG in an estrous synchronization treatment regimen for dairy cattle

There was investigation of whether there were ovulations from co-dominant follicles following eCG administration. In all experiments, there was GnRH injection and CIDR insertion on day 0 (D0), CIDR withdrawal on D8, and cloprostenol administration on D8 (Exp. I and II) or D7 and D8 (Exp. III). Females in the control group were not administered any further treatment. Females in other group(s) were treated with eCG (500 IU) on Day 2 in Exp. I, Day 2 (eCG-2) or 8 (eCG-8) in Exp. II and Day 2 (eCG-2) or Days 2 and 6 (eCG-2-6) in Exp. III. Ovaries were examined using ultrasonography. In Experiments I and II, females had follicle emergence on Day 2. At the time of CIDR removal, more eCG-treated heifers (8/9; Exp. I) and cows (5/6; eCG-2; Exp. II) had co-dominant follicles compared to those in the control group (P < 0.05). Occurrence of ovulations from co-dominant for individual cows was minimal. In Experiment III, the time period from CIDR removal to estrus in cows treated with eCG-2 (68 ± 13 h) was longer compared to cows in the control (37±2 h) and eCG-2-6-treated group (38 ± 5 h; P < 0.05). There was a greater proportion of heifers having ovulations and thus greater progesterone concentration in the eCG-2-6 than eCG-2 group (P < 0.05). Administering eCG twice 4 days apart with the initial administration being two days after GnRH administration, at the time of follicle wave emergence, could induce growth of and ovulation from co-dominant follicles and enhance progesterone production in cattle.

Effects of Equine Chorionic Gonadotropin on Ovulatory and Luteal Characteristics of Mares Submitted to an P4-Based Protocol of Ovulation Induction With hCG

The aim of this study was to evaluate the effect of equine chorionic gonadotropin (eCG) at the end of progesterone (P4) treatment on follicular and luteal characteristics during transition period (TP) and reproductive breeding season (RP). A total of 13 crossbred mares were distributed in two experimental groups in the spring and summer (n = 26). The animals received intravaginal P4 (1.9 g) releasing device from D0 to D10. On removal of P4 device, the mares received 400 IU of eCG (eCG group) or saline solution (control group). Human chorionic gonadotropin (hCG; 1.750 IU) was administered (DhCG) as soon as ovulatory follicle (OF) ≥35 mm was detected. Ovarian ultrasonography was performed from D0 until 15 days after ovulation. Blood samples were collected on D0, D5, D10, DhCG, 9 days after ovulation (CL9D), and 13 days after ovulation (CL13D). P4 and estradiol concentrations were assessed by chemiluminescence. Data were compared by Tukey test at P < .05. Ovulation rate was similar (P = .096) between seasons (RP = 100%; TP = 70%) but occurred earlier (P = .015) in RP (34.8 ± 10.1 hours) compared with TP (42.0 ± 10.4 hours). Interactions between season and treatment were observed for OF diameter (mm) (RP/control = 36.2 ± 1.8ab; RP/eCG = 32.9 ± 2.8 b; TP/control = 32.2 ± 1.2 b; TP/eCG = 37.2 ± 1.9a; P = .004) and for corpus luteum (CL) diameter (mm) on CL13D (RP/control = 25.4 ± 3.5a; RP/eCG = 22.5 ± 1.8ab; TP/control = 21.6 ± 4.9 b; TP/eCG = 27.4 ± 4.3a; P = .023), although no differences were observed for serum P4 on CL13D (RP/control = 6.0 ± 3.1 ng/mL; RP/eCG = 5.8 ± 0.9 ng/mL; TP/control = 3.6 ± 2.7 ng/mL; TP/eCG = 5.1 ± 2.3 ng/mL; P = .429) or for day of structural CL regression (RP/control = 12.8 ± 1.9; RP/eCG = 12.1 ± 1.1; TP/control = 11.0 ± 1.7; TP/eCG = 13.2 ± 2.0; P = .102). The application of eCG at the moment of P4 implant removal seemed to increase the capacity of luteal maintenance during spring TP. However, eCG treatment was worthless during the breeding season.

Melatonin protects against chronic stress-induced oxidative meiotic defects in mice MII oocytes by regulating SIRT1

Chronic stress which is common in the current society can be harmful to female reproduction and is associated with oocyte defects. However, the underlying mechanisms remain largely unknown. Herein, by using a mouse model of chronic restraint stress, we demonstrated that chronic stress could induce meiotic spindle abnormalities, chromatin misalignment, mitochondrial dysfunction and elevated ROS levels in oocytes in vivo, all of which were normalized by the administration of melatonin. Consistently, melatonin treatment during in vitro maturation also attenuated the meiotic defects induced by H₂O₂ by regulating autophagy and SIRT1, which could be abolished by SIRT1 inhibitor, Ex527 and autophagy inhibitor Bafilomycin A1 (Baf A1). These data indicate that melatonin can mitigate chronic stress-induced oxidative meiotic defects in mice MII oocytes by regulating SIRT1 and autophagy, providing new understanding for stress-related meiotic errors in MII oocytes and suggesting melatonin and SIRT1 could be new targets for optimizing culture system of oocytes as well as fertility management.

Decreasing the dose of equine chorionic gonadotropin does not affect ovarian or pregnancy responses of purebred taurine and crossbred beef heifers

In this study there was evaluation of effects of different doses of equine chorionic gonadotropin (eCG: 200, 300, or 400 IU) administrated at progesterone (P4) plus estradiol-based timed AI (TAI). A total of 1080 heifers were included in the study. There was insertion of the intravaginal P4-device plus administration of 2 mg of estradiol benzoate IM. On D7, 12.5 mg of dinoprost tromethamine IM was administered and on D9, the P4 insert was removed and 0.5 mg of estradiol cypionate IM was administered. Heifers were categorized according to Reproductive Tract Status (RTS; 1-5) and were assigned to one of three treatments: 200 IU (n = 387), 300 IU (n = 357), or 400 IU (n = 336) of eCG. Estrous occurrence was evaluated at TAI 48 h later (D11). A subset of heifers (n = 213) had the largest follicle (LF) evaluated on D9 and on D11, and the formation of a new CL evaluated on D18.There was no effect of eCG treatment on LF on D11 (P = 0.79), occurrence of estrus (P = 0.92), and pregnancy at 30 days after AI (P/AI; 52.2%, 49.8%, and 51.5% for 200 IU, 300 IU, and 400 IU, respectively; P = 0.46). Regardless of the treatment, there was a greater P/AI when heifers had a functional CL, at initiation of the estrous synchronization treatment regimen. It, therefore, is efficacious to reduce the dose of eCG to 300 or 200 IU in purebred taurine and crossbred beef heifers without negative effects on ovarian, estrous or pregnancy responses.

Effect of equine chorionic gonadotropin (eCG) administration and proestrus length on ovarian response, uterine functionality and pregnancy rate in beef heifers inseminated at a fixed-time

The objective of the present study was to evaluate the effect of equine chorionic gonadotropin (eCG) administration associated to different proestrus lengths for Fixed-time AI (FTAI) in beef heifers. In Experiment 1, pre-pubertal heifers (n = 46) received a 6-day estradiol/progesterone-based treatment (J-Synch protocol), and were then allocated into four experimental groups in a 2 × 2 factorial design, to receive or not receive eCG (300 IU) at the time of intravaginal progesterone device removal, and to receive GnRH at 48 h or 72 h after device removal (to induce shortened and prolonged proestrus length, respectively). Endometrial samples were obtained 6 d after ovulation from the cranial portion of the uterine horn. The eCG administration induced greater serum estradiol-17β concentrations before ovulation (P < 0.05) and greater proportion of heifers bearing a competent corpus luteum after ovulation (P = 0.054). Delaying GnRH administration from 48 h to 72 h induced a longer interval from device removal to ovulation (i.e., prolonged proestrus; P < 0.05), larger diameter of the ovulatory follicle, and greater progesterone concentrations on Day 10-11 after ovulation. Heifers in eCG + GnRH72h group had more uterine receptors in luminal epithelium than those in eCG + GnRH48h group (PR and ERα), and than those in No eCG + GnRH72h group (PR) (P < 0.05). No effect of eCG or GnRH treatments was found in endometrial gene expression of progesterone and estrogen receptors. In Experiment 2, a total of 2,598 heifers received the J-Synch protocol associated or not with eCG administration at device removal, followed by FTAI/GnRH at 60 or 72 h after device removal (i.e., prolonged proestrus protocol). Heifers that received eCG had greater P/AI than those not receiving eCG (P < 0.05) and there was an interaction between eCG treatment and time of FTAI. The lowest P/AI was found in those heifers that received FTAI/GnRH at 72 h without eCG treatment at device removal (P < 0.05), and no differences were found between the other experimental groups. In conclusion, prolonging the length of proestrus in J-Synch protocol improves ovulatory follicular diameter and luteal function; and the administration of eCG at device removal improves preovulatory estradiol concentrations and luteal function. Finally, P/AI was enhanced by eCG treatment and the improvement was more evident when FTAI/GnRH was performed at 72 h after device removal.

Effect of eCG on the follicular dynamics and vascularization of crossbred cows with different circulating progesterone concentrations during synchronization of ovulation in an FTAI protocol

ABSTRACT: This study aimed to evaluate the effect of treatment with equine chorionic gonadotrophin (eCG) on the follicular dynamics and function of crossbred cows with different circulating progesterone (P4) concentrations during synchronization of ovulation in a fixed-time artificial insemination (FTAI) protocol. To this end, 30 crossbred cows were submitted to a pre-synchronization protocol to ensure that all of them presented corpus luteum (CL) at the beginning of the protocol, and were evaluated by transrectal ultrasonography (TRUS) to verify the presence of CL. After that, the animals underwent an ovulation synchronization protocol and evaluation of follicular dynamics and vascularization by B-mode and power-Doppler ultrasound (US). High plasma P4 concentrations at the time of ovulation synchronization negatively influenced follicle diameter on day 10 (D10), preovulatory follicle diameter, and preovulatory follicle wall vascularization area (p<0.05). Cows with high P4 concentration at the time of ovulation synchronization that were treated with eCG showed follicle diameter on D10 and preovulatory follicle diameter and wall vascularization area (p>0.05) similar to those of animals with low P4 concentration at the time of ovulation synchronization. Therefore, high P4 concentrations at the time of ovulation synchronization negatively influence follicular diameter and vascularization, and eCG can be used as a strategy to favor better follicular and luteal response in crossbred cows with high P4 concentrations submitted to an FTAI protocol.

Equine Chorionic Gonadotropin Modulates the Expression of Genes Related to the Structure and Function of the Bovine Corpus Luteum

We hypothesized that stimulatory and superovulatory treatments, using equine chorionic gonadotropin (eCG), modulate the expression of genes related to insulin, cellular modelling and angiogenesis signaling pathways in the bovine corpus luteum (CL). Therefore, we investigated: 1—the effect of these treatments on circulating insulin and somatomedin C concentrations and on gene and protein expression of INSR, IGF1 and IGFR1, as well as other insulin signaling molecules; 2—the effects of eCG on gene and protein expression of INSR, IGF1, GLUT4 and NFKB1A in bovine luteal cells; and 3—the effect of stimulatory and superovulatory treatments on gene and protein expression of ANG, ANGPT1, NOS2, ADM, PRSS2, MMP9 and PLAU. Serum insulin did not differ among groups (P = 0.96). However, serum somatomedin C levels were higher in both stimulated and superovulated groups compared to the control (P = 0.01). In stimulated cows, lower expression of INSR mRNA and higher expression of NFKB1A mRNA and IGF1 protein were observed. In superovulated cows, lower INSR mRNA expression, but higher INSR protein expression and higher IGF1, IGFR1 and NFKB1A gene and protein expression were observed. Expression of angiogenesis and cellular modelling pathway-related factors were as follows: ANGPT1 and PLAU protein expression were higher and MMP9 gene and protein expression were lower in stimulated animals. In superovulated cows, ANGPT1 mRNA expression was higher and ANG mRNA expression was lower. PRSS2 gene and protein expression were lower in both stimulated and superovulated animals related to the control. In vitro, eCG stimulated luteal cells P4 production as well as INSR and GLUT4 protein expression. In summary, our results suggest that superovulatory treatment induced ovarian proliferative changes accompanied by increased expression of genes providing the CL more energy substrate, whereas stimulatory treatment increased lipogenic activity, angiogenesis and plasticity of the extracellular matrix (ECM).

Morphology and vascularization of the corpus luteum of peccaries (Pecari tajacu, Linnaeus, 1758) throughout the estrous cycle

The current paper characterizes the changes in morphology and vascularization of the corpus luteum of collared peccaries during the estrous cycle and correlates progesterone synthesis (P4). Twenty females were subjected to a treatment for estrus synchronization; an ear implant containing 1.5 mg of norgestomet was implanted on D0, whereas on D9 the peccaries received an IM injection of eCG 200UI and 50g of PGF2a. The animals were divided into four groups (G1, G2, G3 and G4) and euthanized on post-ovulation days 3, 12, 18 and 22. The ovaries were collected and the corpora lutea were measured and processed for histological and vascular density (Dv). Blood was collected for dosage of P4 serum. The morphology of the ovaries, the corpora lutea and P4 varied significantly during the estrous cycle (P<0.001). There was a significant co-relationship between weight and length of the ovaries and CL (r = 0.66, r = 0.52, P<0.05, respectively) and between weight, length and width of the CL and P4 (r = 0.51, r = 0.54 and r = 0.68, P<0.05, respectively). The luteal Dv was highly influenced by the estrous cycle phase (P<0.0001). The P4 and luteal Dv concentrations were higher in G2 and evidenced maximum secretory activity, with a highly significant correlation (P<0.0001). Assessed lutein parameters may estimate the phase of the estrous cycle in peccaries and the functional activity of the corpus luteum.

Development of a GnRH-PGF2α-progesterone-based synchronization protocol with eCG for inducing single and double ovulations in beef cattle

Experiments were designed to investigate the effect of different doses and timing of an eCG treatment given during GnRH-based synchronization protocols on follicular dynamics and fertility in cattle. In Exp. 1, Angus heifers (n = 50) received a 7-d Ovsynch + progesterone protocol (on d 0, GnRH and progesterone insert were administered; on d 7, progesterone insert was removed and PGF2α was injected; and on d 9.5, GnRH was injected 56 h after progesterone removal) with eCG (0, 300, 500, 700, or 1,000 IU) administered on d 7. In Exp. 2, Angus cows (n = 27) received the same protocol as Exp. 1 and were assigned randomly to receive 0 or 400 IU eCG i.m. on d 2 or 7. In Exp. 3, Angus cows (n = 18) received a 6-d Ovsynch + progesterone protocol and were randomly assigned to receive 0 or 800 IU eCG on d 3 of the protocol (Exp. 3a). A pilot field trial was also performed using the same treatments in suckled Angus-cross cows (n = 72; Exp. 3b). In Exp. 4, beef heifers (n = 200) were assigned randomly to the same treatments as in Exp. 3, but the second GnRH was not given, with Holstein bulls introduced on d 6. In Exp. 5, Angus cows (n = 12) received the same treatment as in Exp. 3, but were not inseminated. Progesterone concentrations were assessed in plasma collected during the estrous cycle following synchronization. Ultrasonography was used to monitor ovarian dynamics and to diagnose pregnancy. In Exp. 1, the mean number of ovulations was affected (P < 0.02) by the dose of eCG and the stage of follicular development when administered. Treatment with eCG on d 2 tended (P < 0.08) to extend the interval from PGF2α to ovulation, but was not successful in inducing double ovulations. In contrast, eCG on d 3 increased (P < 0.01) the number of cows with double ovulation when administered i.m. and increased (P < 0.04) pregnancy rate in single ovulating heifers after bull breeding (68.0 vs. 53.1%). This treatment also elevated progesterone concentrations during the estrous cycle following synchronization. Thus, the mechanism by which administration of eCG on d 3 of the synchronization increased pregnancy rates may be through supporting development of a healthy follicle and subsequent corpus luteum capable of secreting increased concentrations of progesterone during early pregnancy. In conclusion, strategic administration of eCG during a synchronization protocol can be used to improve reproductive performance through increased pregnancy rates in single ovulating animals as well as the induction of twin ovulations for twinning.

Microvascularization of corpus luteum of bovine treated with equine chorionic gonadotropin

This study aimed to evaluate the morphological changes in microvascular density and corpus luteum (CL) vascularization in cows treated with eCG during stimulatory and superovulatory protocols. Sixteen cows were synchronized and divided into three groups: control (n = 6), stimulated (n = 4) and superovulated (n =6), one was submitted to estrous synchronization (ES) and received no eCG (control), and those that were submitted to ES and received eCG before or after follicular deviation (superovulation and stimulation of the dominant follicle, respectively). Ovulation was synchronized using a progesterone device-based protocol. After six days of ovulation, the cows were slaughtered and the ovaries and CL were collected. The CLs were processed and photomicrographs were taken under light microscopy to assess the vascular volume density (Vv) by stereology, and scanning electron microscopy (SEM) was used to perform ultrastructural analysis of the microvasculature. The Vv in stimulated and superovulated cows significantly increased (P ≤ 0.0001) when compared to control, indicating that the eCG is able to induce angiogenic activity in bovine CL. However, no significant differences were observed between stimulated and superovulated cows. The SEM demonstrated ratings indicative of angiogenesis, marked by several button-shaped projections in the capillaries, and the presence of more dilated capillaries in CL treated with eCG. These morphological findings are evidence of an angiogenic effect of the eCG treatment in CL of cows.

FSH up-regulates angiogenic factors in luteal cells of buffaloes

Follicle-stimulating hormone has been widely used to induce superovulation in buffaloes and cows and usually triggers functional and morphologic alterations in the corpus luteum (CL). Several studies have shown that FSH is involved in regulating vascular development and that adequate angiogenesis is essential for normal luteal development. Angiogenesis is regulated by many growth factors, of which vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) have an established central role. Therefore, we have used a combination of in vitro and in vivo studies to assess the effects of FSH on the expression of VEGF and FGF2 and their receptors in buffalo luteal cells. The in vivo model consisted of 12 buffalo cows, divided into control (n = 6) and superovulated (n = 6) groups, and CL samples were collected on day 6 after ovulation. In this model, we analyzed the gene and protein expression of FGF2 and its receptors and the protein expression of VEGFA systems with the use of real-time PCR, Western blot analysis, and immunohistochemistry. In the in vitro model, granulosa cells were collected from small follicles (diameter, 4-6 mm) of buffaloes and cultured for 4 d in serum-free medium with or without FSH (10 ng/mL). To induce in vitro luteinization, LH (250 ng/mL) and fetal bovine serum (10%) were added to the medium, and granulosa cells were maintained in culture for 4 d more. The progesterone concentration in the medium was measured at days 4, 5, and 8 after the beginning of cell culture. Cells were collected at day 8 and subjected to real-time PCR, Western blot analysis, and immunofluorescence for assessment of the expression of FGF2, VEGF, and their receptors. To address the percentage of steroidogenic and growth factor-expressing cells in the culture, flow cytometry was performed. We observed that in superovulated buffalo CL, the FGF2 system mRNA expression was decreased even as protein expression was increased and that the VEGF protein was increased (P < 0.05). In vitro experiments with granulosa cells showed an increase in the mRNA expression of VEGF and FGF2 and its receptors 1 and 2 and protein expression of VEGF, kinase insert domain receptor, FGF receptor 2, and FGF receptor 3 in cells treated with FSH (P < 0.05), in contrast to the in vivo experiments. Moreover, the progesterone production by FSH-treated cells was elevated compared with untreated cells (P < 0.05). Our findings indicate that VEGF, FGF2, and their receptors were differentially regulated by FSH in vitro and in vivo in buffalo luteal cells, which points toward a role of CL environment in modulating cellular answers to gonadotropins.

Aromatase inhibitor treatment with an intravaginal device and its effect on pre-ovulatory ovarian follicles in a bovine model

BACKGROUND

Letrozole, a non-steroidal aromatase inhibitor, prevents the body from producing its own estrogen. The objectives of the present study were to test the hypotheses that letrozole treatment, initiated prior to selection of the preovulatory dominant follicle, will induce the growth of more than one follicle to a pre-ovulatory size, and will delay ovulation.

METHODS

Post-pubertal beef heifers were given two luteolytic doses of PGF (12 h apart) and monitored by ultrasonography for ovulation. Five to eight days later, ovarian follicular wave emergence was synchronized by ultrasound-guided transvaginal follicular ablation (Day 0=wave emergence) and a luteolytic dose of PGF was given 60 and 72 h later. On Day 1, heifers were divided randomly into two groups (n=15/group) and an intravaginal device containing 1 g of letrozole or a blank device (control) was inserted. The intravaginal devices were removed on Day 7, or at the time of ovulation, whichever occurred first. Transrectal ultrasonography and blood sample collection were performed daily from the day of ablation to 12 days after subsequent ovulation.

RESULTS

The mean (+/-SEM) interval from device placement to ovulation was longer in letrozole-treated animals compared to controls (6.1+/-0.25 vs 5.1+/-0.26 days, respectively; P<0.01). Single dominant follicles were present in both groups. The day-to-day diameter profiles of the dominant follicles of the ovulatory wave were larger (P<0.05) and the maximum diameters greater in letrozole-treated heifers (14.6+/-0.51 vs 12.4+/-0.53 mm, respectively; P<0.01). The diameter profile of the corpus luteum (CL) that formed after treatment did not differ between groups; however, plasma progesterone concentrations were higher (P<0.01) in heifers treated with letrozole. Estradiol concentrations were reduced following letrozole treatment (P<0.05), although a preovulatory rise of estradiol occurred in both groups.

CONCLUSIONS

Administration of letrozole with an intravaginal device during growth of the ovulatory follicle delayed ovulation by 24 h and resulted in the formation of a CL that secreted higher levels of progesterone. A sustained-release intravaginal device may be useful for the development of an aromatase inhibitor-based protocol to control ovulation for herd synchronization and to enhance fertility by increasing circulating progesterone concentrations during the first 7 days post-ovulation in cattle.