Context Adequate progesterone levels are crucial for embryo development and maintenance of pregnancy. Aims This study aimed to evaluate the effects of injectable progesterone (iP4) administered 14 days after timed artificial insemination (TAI) on conception at Day 30, maintained pregnancy at Day 60 and pregnancy loss in high-yielding dairy cows. We hypothesized that exogenous iP4 supplementation during the critical period of maternal recognition of pregnancy would enhance conception rates. Methods A total of 382 lactating Holstein cows were subjected to TAI. On Day -11, they received an intravaginal device containing 1.9 g of P4, associated with 10.5 mu g of buserelin acetate (gonadotropin-releasing hormone) and 2 mg of estradiol benzoate. On Days -4 and -2, the animals received 25 mg of dinoprost tromethamine, and on Day -2, the device was removed and 1 mg of estradiol cypionate was administered. On Day 0, TAI was performed. Fourteen days after insemination (Day 14), the cows were divided into two groups: control (n = 186) and iP4 (n = 196, supplemented with 350 mg iP4). Pregnancy diagnosis was performed on Days 30 and 60 post-TAI. The data were analyzed using a mixed-effects model that included fixed effects, random effects and covariates. Key results The conception rates at 30 and 60 days post-insemination were significantly higher (P < 0.05) in the iP4 group (44.7% and 39.2%, respectively) than in the control group (35.1% and 31.7%, respectively). A significant interaction was observed between iP4 supplementation and body condition score, in which cows with body condition scores >2.75 treated with iP4 had a higher conception rate at 30 and 60 days than those in the control group. Pregnancy loss between 30 and 60 days was not affected by treatment. Implications These findings suggest that iP4 supplementation 14 days after artificial insemination may improve fertility in high-producing dairy cows, but they should be interpreted with caution due to the lack of physiological evaluation of the mechanisms underlying the action of exogenous progesterone.

The objective of this study was to evaluate the effects of gonadotropin-releasing hormone (GnRH) administration at the beginning of a fixed-time artificial insemination (FTAI) protocol on ovarian dynamics and haemodynamics, assessed by Doppler ultrasonography, in Holstein cows. Sixteen lactating cows were enrolled and allocated to two experimental groups. After pre-synchronisation, the number of corpora lutea (CL) was quantified, and blood samples were collected for progesterone (P4) measurement at the beginning of the FTAI protocol (day 0; D0). The control group (n = 8) received 5 mL of 0.9% NaCl solution intramuscularly, whereas the GnRH group (n = 8) received 21 & micro;g of buserelin acetate (GnRH analogue). On day 7 of the protocol (D7), ovarian ultrasonographic examination was repeated, and additional blood samples were collected. On day 10 (D10), the diameter and blood perfusion of pre-ovulatory follicles (POFs) were measured. On D0, there was no difference in the number of CLs or P4 levels, whereas on D7, GnRH increased the number of CLs (2.25 +/- 0.17 vs 1.12 +/- 0.17; p = 0.005) and P4 levels (12.22 +/- 0.52 vs 9.38 +/- 0.52 ng/mL; p = 0.001) compared with the control group. On D10, POFs in the GnRH group showed a greater blood perfusion area (16.74 +/- 3.41 vs 7.52 +/- 1.15 mm2; p = 0.031). The use of GnRH on D0 of the FTAI protocol resulted in a significant increase in the number of CLs, P4 levels, and blood supply to pre-ovulatory follicles.

This study compared the reproductive performance of three different programs using conventional fixed-time artificial insemination (FTAI), fixed-time embryo transfer (FTET), and their combined use, considering estrus intensity as a criterion for the reproductive program. Brangus multiparous cows (n = 1.100), 40-50 days postpartum, 4-8 years old, and body condition scores 2.50 of 4.50 underwent a protocol for ovulation synchronization based on progesterone (P4) and estradiol on D0. On D10, one of three Programs I-III was implemented: control FTAI (n = 147 cows), control FTET (n = 617) with embryos from in vitro production (IVP) on D17, or FTAI + FTET (n = 336), where cows with low or no estrus expression were inseminated on D10, similar to Program I, while those with high-intensity expression received one embryo from IVP on D17, similar to Program II. Corpus luteum (CL) size and quality were assessed using B-mode and Doppler ultrasound on D17. The service/utilization rate was higher for FTAI and combined FTAI + FTET than for the conventional FTET. The program that used only FTAI resulted in higher pregnancy at 30 and 60 days, as well as lower pregnancy loss, compared to programs that used embryos. Furthermore, the FTAI + FTET program showed reduced pregnancy loss, compared to the FTET program. In the combined program, the CL was greater in those who received FTET alone than in those who received FTAI alone. A higher proportion of recipients with CL with a high luteal blood perfusion score was observed in the FTET group compared to the FTAI group. Satisfactory reproductive rates can be achieved using conventional FTAI or FTET programs. However, the combined program, associated with monitoring the intensity of estrus expression, is a promising strategy for allocating females with absent or low estrus expression to FTAI, and those with high estrus intensity to FTET. Recipients with high-intensity expression had higher CL quality and, when transferred, maintained satisfactory reproductive performance compared with conventional FTET.

Oxidative stress (OS) induced by an imbalance in reactive oxygen species (ROS) levels in vitro impairs embryonic development. Here, we assessed the effects of alpha-lipoic acid (ALA) in in vitro production media on OS reduction, embryonic development, and cryotolerance of bovine embryos. We evaluated the effects of adding different concentrations of ALA (2.5, 5, 10, and 25 μM) to in vitro maturation (IVM) or in vitro culture (IVC) medium on embryonic development. We also determined the effects of adding ALA (25 μM) to the IVM and IVC medium in the same routine on the development and quality of embryos, ROS levels, and cryotolerance. Embryos were produced in vitro using conventional protocols for each treatment. The inclusion of ALA in the IVM and IVC media did not affect the development or quality of embryos; however, it reduced ROS levels in grade II embryos and increased hatching after 12 h on day 7 in grade I embryos and on day 8 in grade II embryos after warming. These findings prompt questions regarding the potential of ALA in improving embryo metabolism, considering the initial embryo recovery in the first few hours of embryo warming.

This study evaluated oocyte competence, gene expression, and in vitro embryo production (IVEP) in cattle, based on follicular waves. Twenty Bos taurus taurus donors were subjected to ovulation synchronization, starting with intramuscular administration of 2 mg estradiol benzoate and a 1.9 g intravaginal progesterone device on a random estrous cycle day (ten days before synchronized ovulation; D-10). After 3 days, the device was removed, and 150 mu g of D-cloprostenol sodium, 300 IU of equine chorionic gonadotrophin, and 1.0 mg of estradiol cypionate were administered. Day zero (D0) was defined as the day of ovulation, and the ovaries of the females in the crossover design were examined using Doppler ultrasonography. Ovum pick-up was scheduled on days D4, D8, D14, and D18, and the experimental groups were designated as G4 (n = 5), G8 (n = 5), G14 (n = 5), and G18 (n = 5), respectively. The corpus luteum (CL) increased in diameter, perimeter, and area throughout the estrous cycle, with significant differences between G4 and other groups (P < 0.0001). CL vascularization scores on G4, G8, G14, and G18 revealed a gradual increase in peripheral blood flow(1.28, 1.79, 1.67, and 1.86, respectively). The central blood flow was higher in G8 (1.53) and G14 (1.57) than that in G4. Oocytes from each group were analyzed using reverse transcription and quantitative polymerase chain reaction after cumulus cell removal. The effect of group (OPU timing) on follicular growth waves was analyzed using ANOVA, followed by Tukey's post hoc test. All statistical analyses were conducted using Minitab statistical software version 18.1, with the significance level set at P <= 0.05. For evaluation of qPCR data, the 2(-Delta Cq) method was used. Analyses were conducted using SigmaStat 4.0 and MetaboAnalyst 5.0. Differences were considered significant at P < 0.05 and/or FC > 2.0 (upregulated) or FC < 0.5 (downregulated).Total and viable oocyte numbers were lowest in G8 (13.9 and 9, respectively). The average numbers of embryos per donor were 2.58, 2.38, 2.29, and 1.69 G14, G18, G4, and G8, respectively. Gene expression analysis showed downregulation of genes related to apoptosis and lipid metabolism in oocytes retrieved from G14 compared to those from G4, G8, or G18. Oocytes from G18 showed upregulation of genes related to apoptosis control and lipid metabolism, whereas those from G4 and G8 were downregulated. In conclusion, ovum pick-up at the beginning of the second follicular wave can improve IVP efficiency.

The postpartum period presents significant reproductive challenges and remains relatively understudied in beef cattle. This study evaluated the effects of prostaglandin F2α (PGF2α) and injectable progesterone (iP4) on uterine health, ovarian dynamics, and pregnancy per insemination in Nelore cows subjected to timed artificial insemination (TAI) during early postpartum. In Study I, cows at 10 days postpartum (dpp) were randomly assigned to one of four groups: Control (0.9 % NaCl, n = 10); PGF2α (0.5 mg cloprostenol, n = 10); iP4 (150 mg, n = 10); or PGF2α+iP4 (0.5 mg cloprostenol and 150 mg iP4, n = 10). Animals were evaluated for uterine inflammation-based on polymorphonuclear cell count (PMN) and uterine body diameter-at 10 and 30 dpp, and underwent an estradiol/progesterone-based TAI protocol to monitor follicular dynamics. In Study II, which was specifically designed to assess pregnancy outcomes, cows at 22 ± 2 dpp were randomized into the same four treatment groups: Control (n = 520), PGF2α (n = 513), iP4 (n = 521), and PGF2α+iP4 (n = 506). At 10 dpp, PMN counts were similar among treatment groups (p = 0.23) but showed a significant reduction by 30 dpp (p < 0.05). No treatment effect was observed at 30 dpp on PMN counts (p = 0.89) or incidence of subclinical endometritis (p = 0.53). Uterine diameter decreased (p < 0.05) in all groups from 10 to 30 dpp, except in the iP4 group. At 30 dpp, the PGF2α and iP4 groups showed a larger dominant follicle diameter compared to controls. PGF2α-treated cows ovulated earlier (p = 0.01), and those receiving PGF2α tended to respond better to the TAI protocol (p = 0.06). In Study II, the PGF2α+iP4 group achieved the highest pregnancy per TAI rate (354/506; 70 %), outperforming the PGF2α (333/513; 64.9 %), iP4 (331/521; 63.5 %), and Control (325/520; 62.5 %) groups (p = 0.05). Treatment with PGF2α+iP4 in early postpartum Nelore cows improved pregnancy rates following TAI.

This study aimed to assess differences in the immunostaining intensity of follicle-stimulating hormone receptor (FSHr) and leutenizing hormone receptor (LHr) receptors in the ovarian follicles of Bos indicus cows with high or low antral follicle counts (AFCs). Ovaries from cyclic Nelore cows (N = 20) were obtained from a local slaughterhouse and classified based on AFC (≥ 3 mm) into high- (≥ 30 follicles, N = 10) and low- (≤ 15 follicles, N = 10) AFC groups. Immunohistochemical studies were performed for FSHr and LHr. Immunostaining intensity was measured using ImageJ software with the IHC Profiler plugin, and pixel intensity was measured on a scale of 0 (darkest) to 255 (lightest). An interaction was observed between the AFC group and follicular developmental stage for FSHr immunostaining intensity, with preantral follicles from the low-AFC group showing highest immunostaining intensity (p < 0.0001). The FSHr immunostaining intensity of antral follicles from the low-AFC group was higher than that of the high-AFC group (p = 0.03). LHr immunostaining intensity also was higher in the low-AFC group than in the high-AFC group (p = 0.002). These findings suggest that ovarian follicle characteristics of low-AFC cows have distinct characteristics that could affect their response to reproductive treatments.

Competent oocyte is a critical point for successful fertilization and early embryonic development. This systematic review aimed to synthesize scientific evidence from omics studies on oocyte development in cattle during the estrous cycle. Our systematic search followed the PRISMA guidelines, using three databases: PubMed, Scopus, and Web of Science Core Collection. After a critical appraisal of the literature using the Kmet scoring system, ten peer-reviewed articles were included. These studies involved analyses of follicular fluid, cumulus and granulosa cells, oocytes, and maturation media. Transcriptomics predominated among the studies and identified transcriptional patterns associated with oocyte competence in different cell types and stages of the estrous cycle, particularly around the LH surge. In addition, experiments focusing on the ovulatory window as the main theme were identified in the studies. Metabolomic analyses highlighted the role of amino acid turnover and purine metabolism in follicular fluid and maturation media, providing insights into potential biomarkers in oocyte development. The results emphasized the importance of nucleotide metabolism, extracellular matrix interactions, and hormonal signaling pathways, particularly involving genes such as INHBA, TNFAIP6, and TRIB2, in regulating oocyte maturation. This review underscores the power of integrating omics data to elucidate complex molecular mechanisms relevant to the acquisition of oocyte competence. Furthermore, it explores the identification of potential molecular markers that would aid the development of protocols and culture media, while aiming to improve oocyte quality and advance assisted reproductive technologies.

This study aimed to evaluate the effect of prostaglandins on the proportion of inflammatory cells (PMN) and postpartum pregnancy rates in cows subjected to fixed-time artificial insemination (FTAI) programs. In total, 209 postpartum Nelore cows were used in this study. Females were separated into three groups to receive the following treatments: control group- CTL (n = 66), females that were not treated; group 0.5 PG (n = 68), cows that received cloprostenol 0.5mg – a PGF2α analog; and group 1.0 PG (n = 75), cows that received 1mg of cloprostenol. All females were subjected to the FTAI protocol at an average of 38.7 ± 7.6 (Mean ± SD) days postpartum (DPP). Uterine health was assessed using polymorphonuclear cell (PMN) counts. On Day 0 of the FTAI protocol (D0), material was collected using disposable cervical brushes for cytology and analysis of the proportion of inflammatory cells (PMN) recovered from the endometrium in the cervical region. Pregnancy diagnosis was performed by transrectal ultrasonography 30 days after FTAI. Logistic regression was used to analyze the effects of treatment, category, and their interactions on Pregnancy/Artificial Insemination (P/AI). The proportion of PMN cells according to the group was analyzed using ANOVA (PROC GLIMMIX; SAS Inst. Inc., Cary, NC, USA), and the means were compared between groups using Tukey’s test. A level of 5% was considered significant. The proportion of PMN did not differ among the groups. The overall pregnancy rate was 72.2% (151/209). No effects of group (P = 0.51) or category (P = 0.84) were detected on the P/AI among the groups. There was a tendency (P = 0.07) for a group-category interaction for P/AI. In this regard, the P/AI in multiparous cows treated with 1mg of PGF2α tended to be higher (P = 0.08) than that in the control cows.

Mares (n = 77) were evaluated by antral follicle count (AFC) and selected as embryo recipients. Cyclic recipients received embryos between days 4-6 after ovulation. The acyclic recipients received an intramuscular (i.m.) protocol with 5mg of estradiol benzoate (EB) on the day of donor ovulation (D0; D-4 recipient), 3mg of EB on the following day (D1; D-3 recipient), and 3mg of EB (D2; D-2 recipient). Furthermore, 1500mg of progesterone (P4) i.m. given on D0 of the recipient (D4 donor) followed by 1500mg of P4 on the day of ET (D4-6 recipient). On the ET day, the AFC and animals' weight, body condition score (BCS), corpus luteum diameter, age and degree of uterine edema (UE) were measured. Pregnancy was confirmed on days 12 and 30. Low AFC was defined as ≤11 follicles (n = 43 mares) and high AFC as >11 follicles (n = 34 mares). Data were analyzed by a mixed effect model, including AFC group, reproductive seasonality, and season (P ≤ 0.05). UE was influenced (P = 0.05) by reproductive seasonality. The conception rate was higher (P = 0.016) in recipients with low (79.07 %) than high AFC (61.76 %) and higher (P = 0.005) in cyclic (81.40 %) than anestrus (58.82 %) mares. In addition, we observed a tendency (P = 0.06) for the interaction of AFC*reproductive seasonality, showing that high*anoestrus recipients had the lowest conception rate (37.50 %b) compared to high*cyclic (83.33 %a), low*anoestrus (77.78 %a) and low*cyclic (80 %a). The conception rate was higher in cyclic recipients with low AFC. Furthermore, UE was influenced by reproductive seasonality and mares in anestrus showed a higher degree of UE than cyclic mares.

Pregnancy losses negatively affect the cattle industry, impacting economic indices and consequently the entire production chain. Early embryonic failure has been an important challenge in the embryo industry because proper identification of embryo death at the beginning of gestation is difficult. This review aimed to provide a better understanding on reproductive failure and the relationship between early embryonic loss and different reproductive biotechniques. This review also considers insights and possible strategies for reducing early embryonic loss. The strategies addressed are as follows: i) great impact of rigorous embryo evaluation on reducing embryo losses; ii) selection of recipients at the time of transfer, taking into account health and nutritional status, and classification of the corpus luteum using ultrasound, either in area or vascularization; and iii) paternal effect as one of the factors that contribute to pregnancy losses, with a focus on embryo transfer.

There is a growing regulatory and scientific interest in the studies of environmental substances that are capable of interfering with the reproductive system. Among them, parabens stand out due to their widespread use and frequent detection as contaminants in human tissues and biological fluids. Therefore, we evaluated the toxic effects of butylparaben on the viability and follicular staging of bovine ovarian follicles in vitro. Fragments of ovaries from five cyclic bovine females were cultured for 44 h in a minimal essential medium (MEM; control) or MEM supplemented with 50 µg/mL and 100 µg/mL of butylparaben (BP 50 and BP 100 groups, respectively). The ovarian fragments were subjected to follicular staging, morphological analysis, morphometric analysis, estradiol analysis and oxidative profiling. No significant changes were observed between the experimental groups in follicular staging, estradiol analysis and oxidative profile analysis. However, the BP 50 group showed a significant decrease in the number of intact ovarian follicles. Moreover, a decrease in the follicular and oocyte diameters was observed in the groups that were exposed to butylparaben. In conclusion, butylparaben impairs the integrity and size of ovarian follicles in an in vitro bovine model, but does not affect the oxidative profile and steroidogenesis.

This study evaluated the effect of prostaglandin F2α (PGF2α) associated with gonadotropin-releasing hormone (GnRH) for ovulation induction in precocious indicus heifers submitted to a fixed-time superovulation (SOV) programme. Precocious Nellore heifers (n = 35), aged 13 months, were subjected to the SOV protocol. On day 0 (D0), all animals received intravaginal insertion of a progesterone (P4) device along with intramuscular administration of 2 mg of oestradiol benzoate, plus 200 IU of follicle-stimulating hormone in decreasing doses, with 12-h intervals between D4 and D7, in addition to 150 μg of D-cloprostenol on D6 and device removal on D7. On D8, the donors received 10.5 μg of buserelin acetate and the treatment group received 300 μg of D-cloprostenol/PGF2α. Artificial insemination was performed 12 h and 24 h after GnRH administration using frozen semen. On D15 of the protocol (i.e., D7 after insemination), the embryos were collected and evaluated. All animals passed through the control and treatment groups. Results were evaluated by analysis of variance using an adjusted mixed-effects model (p < 0.05). There was no difference in the total number of embryos between the control and treatment groups (10.40 ± 1.52 vs. 9.60 ± 1.36; p = 0.63) or viable embryos (6.30 ± 1.22 vs. 4.30 ± 0.71). For precocious indicus heifers, treatment with PGF2α in association with GnRH did not affect embryo production in the fixed-time SOV protocol.

This study evaluated the effects of pre-synchronisation with injectable progesterone (P4) on the ovarian follicular dynamics of Bos taurus indicus cows in anoestrous treated with a timed artificial insemination (TAI) protocol. Multiparous Nelore females (n = 47) at 30-60 days postpartum were used in this study. 10 days before (D-10) the TAI protocol, antral follicle count (AFC; follicles >= 3 mm), ovarian condition and body condition score (BCS; 1-5) were assessed and were randomly allocated into two groups: Pre-sync (n = 25), which underwent pre-synchronisation with 150 mg of injectable P4 intramuscularly (i.m.), and control (n = 22), which received the same volume of NaCL 0.9%. On D0, the ovarian assessment was repeated, and TAI protocol was initiated in all animals, with the insertion of an intravaginal P4 device and administration of 10.5 mu g of buserelin acetate (gonadotropin-releasing hormone-GnRH). On D7, the P4 device was removed, and 300 IU of equine chorionic gonadotropin, 150 mu g of D-cloprostenol and 1 mg of estradiol cypionate were administered i.m. On the same day (D7), the presence of the corpus luteum (CL) was assessed, the dominant follicle was measured, and the tail was painted to evaluate estrous expression. On D9, the largest follicle was remeasured, and TAI was performed. Animals that were not detected in oestrous at the time of AI were administered 10.5 mu g of GnRH i.m. Numerical data were analysed using the Mann-Whitney U test. Binary data were analysed using the Fisher's exact test (5%). BCS, both at the beginning of pre-synchronisation (p = 0.45) and TAI protocol initiation (p = 0.20), and AFC (p = 0.36) did not differ between control and Pre-sync groups. The diameter of the largest follicle was similar between the control and Pre-sync groups on D-10 (p = 0.32), D0 (p = 0.33), D7 (p = 0.29) and D9 (p = 0.22). On D7 of the protocol, the Pre-sync group had a higher percentage of CL visible on transrectal ultrasonography (84.0%; p = 0.02) than the control group (54.5%); however, the expression during oestrous did not differ between groups (p = 0.59). The pregnancy rate was similar (p = 0.64) between groups and was not influenced by the CL rate on D7 (p = 0.48), oestrous expression (p = 0.20) or their interaction (p > 0.1). Pre-synchronisation effectively increased the proportion of cows with CL on D7 without altering the diameter of the largest follicle, oestrous expression or pregnancy rate in anoestrous cows treated with a GnRH/P4-based TAI protocol.

The C-type natriuretic peptide (CNP) plays a central role in regulating the meiotic progression of oocytes into growing follicles in mammals. However, there are few reports examining the relationship between CNP and embryonic development. In our study, different concentrations (50, 100, or 150 nM) of CNP were added during in vitro maturation (IVM) of cumulus-oocyte complexes (COCs) or in vitro culture (IVC) of the bovine embryos (B. taurus indicus). The effects on embryo production and transcript abundance of the 20 genes of greatest interest that are related to metabolism, oocyte maturation, follicular development, cell signaling, oxidative and thermal stress, maternal-fetal interaction, and epigenetic regulation were evaluated. The blastocyst rate was influenced by CNP treatment (P=0.049). Blastocyst rates were 31.05% (136/438) in the control group, 33.47% (162/484) in the 50 nM treatment group, 35.24% (179/508) in the 100 nM treatment group, and 32.53% (162/498) in the 150 nM treatment group for IVM. Furthermore, with IVC CNP supplementation, blastocyst rates were 28.49% (100/351) at 50 nM, 27.67% (119/430) at 100 nM, and 26.92% (112/416) at 150 nM. Moreover, the expression of RE1 silencing transcription factor (REST), a gene related to pluripotency and to embryonic development, was greater (P=0.028) in response to 150 nM CNP supplementation in IVM. Finally, we observed for the first time the expression of the CNP receptor (NPR2) in embryos and the possible action of CNP at this stage. In conclusion, our data provide a reference for the improvement of IVM results in the in vitro production of bovine embryos with supplementation with 100 nM CNP, and this is the first study to demonstrate the expression of the CNP receptor (NPR2) in bovine embryos.

This study compared the reproductive performance of embryo recipients treated with a timed embryo transfer (TET) protocol using human chorionic gonadotropin (hCG) or equine chorionic gonadotropin (eCG). On a random day of the estrous cycle (Day -10) indicus-taurus recipients (n = 341; 194 nulliparous and 147 multiparous cows) with a body condition score between 3.0 and 4.0, were submitted to the TET protocol consisting of an intramuscular (i.m.) injection of 2.0 mg estradiol benzoate (EB) and the insertion of intravaginal progesterone (P4) device that remained until Day -2.5. On the same day (-2.5), the recipients received i.m. 150 mg D-cloprostenol and 1 mg estradiol cypionate and were randomly divided into two groups: the eCG group (n = 179), in which females received i.m. 300 IU eCG and the hCG group (n = 162), in which females received 150 IU hCG. Then, estrus intensity and the diameter of the dominant follicle (DF) were monitored on D0 and the quality of the corpus luteum (CL) (B mode and color Doppler) was assessed on D7 to select recipients eligible for receiving the transfer of an embryo produced in vitro. Pregnancy diagnosis was assessed 23 days after the transfer. Continuous data were analyzed by ANOVA using a mixed-effects model and Tukey's test. The rates were analyzed using a lo-gistic regression model. The diameter of the DF on day 0 of the TET protocol was influenced by the interaction between gonadotropic treatment and category (P = 0.01), and nulliparous recipients treated with hCG had the smallest diameter. Treatment with hCG and eCG resulted in a high rate of estrus expression; however, the proportion of females with a high-intensity of estrus was higher in the hCG group (79.84 vs. 68.61%, respectively; P = 0.03). The utilization rate (recipients with CL) showed a tendency (P = 0.06) to be influenced by the interaction between gonadotropic treatment and category, wherein nulliparous recipients treated with hCG exhibited a lower utilization rate than the other groups. The diameter, perimeter, and area of the CL were similar (P > 0.1) in all groups. However, the hCG group resulted in CL with a better Doppler evaluation score (P = 0.04), central blood flow (P = 0.03), and tendency towards greater peripheral blood flow (P = 0.08). The rates of conception (32.00% hCG vs. 35.10% eCG; P = 0.46) and pregnancy (24.69% hCG vs. 29.61% eCG; P = 0.20) were similar between the hCG and eCG groups. However, an interaction between the gonadotropic treatment and category revealed lower conception (P = 0.01) and pregnancy rates (P = 0.001) in nulliparous recipients treated with hCG. Treatment with hCG resulted in a greater intensity of estrus expression and CL with a higher Doppler score, which determined rates of utilization, conception, and pregnancy similar to conventional protocols using eCG. However, nulliparous recipients treated with hCG exhibited a lower overall reproductive rate.(c) 2022 Elsevier Inc. All rights reserved.

The ovary is a dynamic structure with two main functions. First, the ovary is responsible for producing hormones that control and direct the female reproductive system. Second, it is in the ovary that folliculogenesis and oogenesis take place. Such processes begin in prenatal life and comprise the formation, growth, and maturation of the follicular and female gamete, culminating in the release of a mature oocyte for fertilization. However, only 0.1% of the follicles reach the stage known as pre-ovulatory and are fertilized, thus underutilizing the female reproductive potential. Here we review recent advances in oogenesis and folliculogenesis. First, we review mechanisms of formation, growth, and development of follicles. We discuss the influence of the antral follicle count in the reproductive performance in cattle. Finally, we present recent hypotheses about follicular renewal and new insights on epigenetic modifications during folliculogenesis.

This study aimed to evaluate the effect of luteal blood perfusion and corpus luteum (CL) area on the conception rate and occurrence of pregnancy loss of recipients in a large-scale fixed-time embryo transfer (FTET) program. Multiparous Brangus cows (n = 1700) at 45 days postpartum and body condition scores (BCS) between 2.5 and 4.0 (3.0 ± 0.3) were used in this study. On a random day of the estrous cycle (day -10), the females received progesterone and estradiol based on the FTET protocol. On day 7, 1465 recipients had at least one CL and were evaluated using B-mode ultrasound for the CL area (cm2) and color Doppler for the luteal blood perfusion score (I/low-vascularization area <40% of the CL; II/medium-vascularization >45% to < 50%; and III/high-vascularization >50%). Immediately after CL evaluation, each recipient received a single fresh embryo (blastocyst stage) ipsilateral to the CL, in vitro produced from a commercial laboratory. Pregnancy diagnosis was performed at 30 days and repeated 60 days later to evaluate pregnancy loss (30-90 days). Ultrasound evaluation and embryo transfer were performed by a single technician. For data analysis, in addition to luteal blood perfusion groups, recipients were retrospectively ranked according to CL area into small (<3 cm2; 2.63 ± 0.01), medium (>3 to < 4 cm2; 3.44 ± 0.01), and large (>4 cm2; 4.77 ± 0.03). Data were analyzed using a logistic regression model (P < 0.05). The overall conception rate was 44.2% (648/1465), influenced by the luteal blood perfusion score [P = 0.03; high 48.4%a (134/277), medium 44.6%a (427/958), and low 37.8%b (87/230)] but not by CL area ranking [P = 0.37; large 41.8% (225/538), medium 45.2% (276/610), and small 46.4% (147/317)]. There was no interaction between the luteal blood perfusion score and CL area ranking (P = 0.81), and the BCS did not affect the results of this study (P = 0.51). In terms of pregnancy loss up to 90 days, there was no effect on the CL area ranking (P = 0.77), but the flow score showed an effect [P = 0.03; high 3.6%b (5/139), medium 9.3%a (44/471), and low 10.3%a (10/97)]. The conception rate and occurrence of pregnancy loss in the FTET program in beef cattle are related to luteal blood perfusion but not CL size.

Abstract The objective of this work was to investigate whether puberty and parturition alter the antral follicle count (AFC) in female Nelore (Bos indicus) beef cattle. Two experiments were carried out to compare AFC between the prepubertal and pubertal periods and between the prepubertal and postpartum periods. AFC and follicle concentrations did not differ between the prepubertal and pubertal periods. However, the ovarian area increased after puberty. In addition, AFC and the ovarian area were greater in the postpartum than in the prepubertal period. Therefore, AFC is not affected by the puberty of Nelore heifers, but increases significantly when the prepubertal heifers become cows.