Increased pregnancy rate in beef heifers resynchronized with estradiol at 14 days after TAI

Effects of estradiol on PGF2α synthesis and corpus luteum function during early pregnancy in beef heifers

This study investigated the effects of estradiol benzoate (EB) administered 13 days post-ovulation on PGF2α release and corpus luteum function in pregnant and non-pregnant heifers. In Exp. 1, Nelore (Bos indicus) heifers, either inseminated or non-inseminated, were randomly assigned on Day 13 (D13) to receive 0, 1, or 2 mg of EB. Blood samples were collected at baseline (H0) and hourly from H3 to H12 to assess plasma P4 and PGFM concentrations. In a subgroup of pregnant heifers, blood samples were also collected to determine plasma E2 concentrations. Doppler ultrasonography was performed daily from D13 to D19 for monitoring the luteal function, and pregnancy was determined on D28. Luteolysis was earlier (P < 0.05) in non-inseminated heifers treated with 1 or 2 mg EB than in the controls (16.3 ± 0.2 vs. 17.3 ± 0.6 days). Pregnancy rate was lower (P < 0.05) in the EB-1 (50 %; 8/16) and EB-2 (29.2 %; 7/24) groups than in the EB-0 group (90 %; 9/10). The average PGFM concentrations were greater (P < 0.05) in the EB-1 and EB-2 groups than in the EB-0 group, regardless of gestational status. In Exp. 2, inseminated (n = 39) and non-inseminated (n = 21) Nelore heifers received either 0 or 1 mg of EB on D13. Three hours later, endometrial cytology was performed and samples were evaluated by qPCR. Expression of OXTR and PGR was greater and IL1β was lower in EB-treated heifers (P < 0.05). The ESR2 abundance was lower (P < 0.05) in pregnant heifers, regardless of EB treatment. In conclusion, an elevation of circulating E2 at late diestrus upregulates the OXTR and PGR expression in the endometrium, inducing PGF2α release and luteolysis, which negatively impact on pregnancy establishment, especially in heifers treated with 2 mg EB.

Evolution over the last 40 years of the assisted reproductive technologies in cattle - the Brazilian perspective for embryo transfer and resynchronization programs (part II)

The productivity of the beef and dairy industries depends directly on the reproductive efficiency and genetic gain of the herd, which are directly associated with the appropriate use of Assisted Reproductive Technologies (ARTs). The objective of this review is to show from a Brazilian perspective the evolution over the last 40 years of ARTs related to ovulation resynchronization programs and embryo transfer in cattle. Despite significant improvements and high fertility obtained in timed artificial insemination (TAI) protocols (Sales et al., 2024 - Part I), the improvement of the use of in vitro-produced embryos, development of resynchronization programs, and the advance in Doppler ultrasonography (Doppler-US) for reproductive assessments of bovine females were the ARTs that presented the greatest relevance on reproductive effectiveness in cattle. In the last seven years, the embryo transfer (ET) technology using in vitro-produced (IVP) embryos took over the conventional ET of in vivo produced embryos after donor's superovulation. Also, procedures and pregnancy rates after ET of IVP embryos were improved in dairy and beef operations. The Doppler-US allows the identification of non-pregnant females at an early stage based on the evaluation of blood perfusion of the corpus luteum. Recent studies in beef and dairy cows indicate satisfactory accuracy when Doppler-US is used at 20-22 days after TAI. Consequently, super-early resynchronization programs have been developed and are being implemented in commercial programs, thereby facilitating earlier conception through the use of semen from superior bulls, providing genetic and economic improvements in herds. Likewise, the assessment of luteal function by Doppler-US allows the selection of embryo recipients with greater receptivity, and consequently may increase the effectiveness of timed ET programs.

Optimizing ReBreed21 II: Fertility and reproductive efficiency in different parities during a shortened breeding season in beef cattle

This study evaluated the efficiency of a rapid reinsemination program allowing timed AI (TAI) every 21d (ReBreed21) in a commercial beef cow-calf operation. Nelore females from different parities (n = 2085) were synchronized for first TAI (D0 = TAI) using an estradiol/progesterone (E2/P4) protocol and assigned to one of three reinsemination programs: Resynch33 (n = 753), traditional resynch program with second TAI at D42 after first TAI; ReBreed21 (n = 687); or ReBreed21+EC (n = 670). The ReBreed females (n = 1357) received intravaginal P4 insert on D12, on D19 P4 was removed, and a dose of equine chorionic gonadotropin (eCG) was administered, then, ReBreed21 females received 0.6 mg of EC (ReBreed21+EC) or nothing (ReBreed21) and on D21, nonpregnancy (NP) was determined using Doppler ultrasound to detect corpus luteum (CL) blood flow (BF) (NP: <25 % BF pixels of total CL area) and NP cows received immediate TAI and GnRH to induce ovulation. Pregnancy diagnosis was performed at D33 after TAI following all TAIs. Cows considered pregnant at D21, based on CL BF, but NP on D33 were designated False-Positives (FP) and false negatives (FN) were number of nonpregnant cows/heifers on d21 based on the CL BF found to subsequently be pregnant on D33 divided by the total number pregnant. Pregnancy/AI (P/AI) did not differ for the first TAI (55.1 %) among the treatments. Heifers had similar P/AI at the second AI in all groups and similar to the first AI. Primiparous had greater P/AI in ReBreed21+EC and Resynch33 at s TAI compared to ReBreed21, 51.7 %, 55.8 %, 34.2 %, respectively. Multiparous had greater P/AI at second TAI in Resynch33 (60.9 %) than ReBreed21 programs (34.7 %). The percentage FP and FN among ReBreed21 programs did not differ, 13.8 and 0.2 %, respectively. Overall accumulative pregnancies on D21 of the breeding season were greater for ReBreed21 and ReBreed21+EC than Resynch33 (69.7 %, 71.6 %, and 55.5 %, respectively). However, on D42 of the breeding season, only heifers had greater pregnancies in ReBreed21 programs than Resynch33 (73.3 %, 74.3.6 %, and 63.2 %, respectively). Average days to pregnancy were less (P = 0.01) for ReBreed21 and ReBreed21+EC than Resynch33. Thus, the ReBreed21 strategy can improve the efficiency of TAI programs in beef cattle. Of interest, ReBreed21 was particularly effective in nulliparous, somewhat effective in primiparous when EC was added to the program, but relatively ineffective in multiparous beef cattle.

Viperin (RSAD2) gene expression in peripheral blood mononuclear cells of pregnant crossbred beef cows is altered by Bos indicus genetics

The expression of interferon (IFN) stimulated genes (ISGs) in lymphocytes has been used for pregnancy diagnosis in cattle. However, among-cow variability has yielded sub-optimal predictive accuracy. We hypothesized that the expression of ISGs (ISG15, OAS1, RSAD2, CLEC3B, and AKR1B1) in early pregnancy varies according to the proportion of Bos indicus (B. indicus) genetics on females. Multiparous cows were classified in three genetic groups, High Angus (HA; n = 45 [0-33% Brahman influence]), Angus-Brahman (AB; n = 30 [34-67%]), and High Brahman (HB; n = 19 [68-100%]) and submitted to a Select-Synch + CIDR protocol. Cows that displayed estrus (n = 94) were artificially inseminated (Day0; D0). On D19, blood samples were collected to obtain peripheral blood mononuclear cells (PBMC) and measure progesterone (P4) concentrations. On D30, pregnancy diagnosis was performed. The expression of RSAD2 in PBMC of pregnant cows was positively related to the proportion of B. indicus genetics of the groups, but not the expression of ISG15 and OAS1. In pregnant cows, the proportion of B. indicus genetics was negatively associated to circulating levels of P4 concentrations. The P4 concentrations were related positively with RSAD2 expression. ROC curve results determined that for cattle with B. indicus genetics lower than 67%, the CLEC3B and AKR1B1 combination was the most accurate option to predict the outcome of pregnancy. In cows with more than 68% of B. indicus genetics, RSAD2 provided the best accuracy. In conclusion, there is a relationship between the proportion of B. indicus genetics and the ISGs gene expression in PBMC during pregnancy.

Review: Current status of corpus luteum assessment by Doppler ultrasonography to diagnose non-pregnancy and select embryo recipients in cattle

A number of potentials uses of Doppler ultrasonography have been explored in the last decades, both as research tools in reproductive physiology investigations and for the reproductive management of farm animals. The objective of this review was to address some of the recent strategies developed in fixed-time reproductive programs and resynchronization of ovulation in cattle, based on the evaluation of corpus luteum function by color-Doppler ultrasound imaging. Recent studies in dairy and beef cattle pointed out to a high accuracy when Doppler ultrasonography is used to assess the functionality of the corpus luteum and identify non-pregnant females at 20-24 days after breeding. Therefore, super-early resynchronization programs starting in the second week after timed-artificial insemination or embryo transfer have been developed and are being implemented in commercial assisted reproduction programs; thus, anticipating conception with proven semen or genetically superior embryos. In addition, assessment of corpus luteum blood perfusion can be used for identifying high fertility embryo recipients in fixed-time embryo transfer programs.

Applied Use of Doppler Ultrasonography in Bovine Reproduction

The use of Doppler ultrasonography to quantify blood vascularization in reproductive organs has increased over the past decade. Doppler technology has predominantly been explored in research settings to evaluate uterine blood flow and to assess follicular and luteal blood perfusion. Recent research has also explored the use of Doppler technology in applied reproductive management for both the beef and dairy industries and has focused on the use of luteal color Doppler ultrasonography to evaluate embryo transfer recipients and perform early pregnancy diagnosis. Although significant progress has been made and current literature indicates a strong potential for the applied use of Doppler ultrasonography to increase reproductive efficiency in the cattle industry, uptake of this technology is still currently limited. This review summarizes the recent developments in the applied use of color Doppler ultrasonography for reproductive management in both beef and dairy cattle herds.

Luteal color doppler ultrasonography and pregnancy-associated glycoproteins as early pregnancy diagnostic tools and predictors of pregnancy loss in Bos taurus postpartum beef cows

The objective of this study was to evaluate the use of luteal color doppler (CD) ultrasonography and plasma concentrations of pregnancy-associated glycoproteins (PAG) for early pregnancy diagnosis in Bos taurus beef cows. Additionally, CD and PAG were evaluated as potential predictors of late embryonic/early fetal mortality (LEM). Postpartum beef cows (n = 212) were exposed to estrus synchronization followed by fixed-time artificial insemination (day 0). On days 20 and 22, B-mode and CD ultrasonography were performed to evaluate corpus luteum (CL) morphometries and blood perfusion. Moreover, blood samples were collected on days 25 and 29 to quantify circulating concentrations of PAG. Conventional ultrasonography on days 29 and 100 was utilized as the gold-standard method for pregnancy diagnosis. Cows that experienced pregnancy loss between days 29 and 100 were classified as LEM. Pregnant cows had larger and more vascularized CL compared with nonpregnant cows on days 20 and 22 (P < 0.001 for all response variables). Accuracy for CD on days 20 and 22 were 87% and 92%, respectively. Accuracy for PAG on days 25 and 29 were 84% and 99%, respectively. No false negative (FN) results were observed for CD on both days 20 and 22; however, there were 7.1% FN results for PAG on day 25. Cows that experienced LEM had decreased (P = 0.04) circulating PAG on day 29 of gestation compared with cows that maintained pregnancy; however, there were no differences in luteal blood perfusion on days 20 and 22 (P ≥ 0.53) or circulating PAG on day 25 (P = 0.46) between LEM cows and cows that maintained pregnancy. Sensitivity and specificity of PAG on day 29 as predictors of LEM were 83% and 77%, respectively. In conclusion, CD resulted in accurate pregnancy diagnosis in B. taurus beef cows on both days 20 and 22 of gestation, while having no FN results. Circulating concentrations of PAG were decreased in cows that experienced LEM; however, further research is required to utilize PAG as a predictor of LEM commercially.

A comparative transcriptome and proteomics study of post-partum ovarian cycle arrest in yaks (Bos grunniens)

Post-partum ovarian cycle arrest is the main factor affecting yak reproductive efficiency. There are few reports regarding the molecular regulatory mechanism of post-partum oestrus at transcriptome and proteome levels in yaks. Our previous studies focussed on the ovaries of yaks with post-partum ovarian cycle arrest and post-partum oestrus yaks. In this study, RNA sequencing transcriptomic study was combined with quantitative proteomic analyses to identify post-partum ovarian cycle-related genes and proteins. Consequently, 1,149 genes and 24 proteins were found to be up- or downregulated during post-partum oestrus. The analysis of differentially regulated genes identified three gene or protein pairs that were synchronously upregulated and no gene or protein pairs that were synchronously downregulated, suggesting that these upregulated genes may regulate the post-partum ovarian cycle. The functional classification of these differentially expressed genes and proteins indicated their connection with the oocyte meiosis, the oestrogen signalling pathway, the progesterone-mediated oocyte maturation and the gonadotrophin-releasing hormone (GnRH) signalling pathway. In this study, a total of six genes and two proteins involved in the oocyte meiosis, the oestrogen signalling pathway, the progesterone-mediated oocyte maturation and the GnRH signalling pathway were identified. The CSNK1A1, M91_09723, M91_11326, M91_21439, M91_19073, SHC2, Atf6b, M91_03062, HSPCA and calmodulin could regulate oestrus, respectively, in the post-partum so as to control the anoestrus status.

Resynchronization of follicular wave using long-acting injectable progesterone or estradiol benzoate at 14 days post-timed AI in Bos taurus x Bos indicus beef heifers

We compared pregnancy rates in beef heifers resynchronized 14 days after the first timed-artificial insemination (TAI) using a P₄ intravaginal device associated with either long-acting injectable progesterone (iP₄) or estradiol benzoate (EB). Braford and Brangus heifers were submitted to a TAI (D0). On D14, all animals were given a P₄ intravaginal device and were randomly divided into two groups, EB (1 mg; n = 339); or iP₄ (75 mg; n = 338). On D22, P₄ devices were removed, and non-pregnant (NP) heifers were identified by assessing morphological luteolysis with Doppler ultrasonography. The NP heifers had the dominant follicle diameter measured and were submitted to a second TAI on D24. Dominant follicle diameter (mm) on D22 in NP heifers did not differ (P > 0.05) between EB (9.77 ± 0.25) and iP₄ (9.92 ± 0.22) groups. No difference was observed between EB and iP₄ groups for pregnancy rate on D22 (56.3% vs. 60.1%, respectively), and D40 post-first TAI (49.6% vs. 53.3%, respectively). The rate of potential pregnancy losses from D22 to D40 did not differ between EB (12%, 23/191) and iP₄ (11.3%, 23/203) groups. The resynchronization pregnancy rate in the EB group (45.9%, 68/148) was greater (P<0.05) than the iP₄ group (31.8%, 43/135). In conclusion, treatment with either 1 mg EB or 75 mg iP₄ in combination with P₄ device at 14 days after TAI are equally safe for the ongoing pregnancy. The EB treatment can improve the reproductive efficiency, as it resulted in greater resynchronization pregnancy rates than iP₄ treatment in beef heifers resynchronized 14 days after TAI.

Effects of estradiol treatments on PGF2α release in beef heifers submitted to estrous resynchronization 14 days after timed-AI

The effects of 17β-estradiol (E2) or estradiol benzoate (EB) on PGF2α release were studied in bred-non-pregnant and pregnant Nelore beef heifers. The day of timed artificial insemination (TAI) was designated day 0 (D0), and a single treatment was given on D14. All heifers also received an intravaginal P4 device on D14, and were randomly assigned to three groups: Control (C, P4 device only, n = 12); E2 (1 mg E2 + 9 mg P4, n = 10); or EB (1 mg, n = 10). Blood samples were collected hourly for 8 hours after treatment (Hours 0-8) to measure plasma concentrations (pg/mL) of a PGF2α metabolite (PGFM). The P4 device was removed on D22 and pregnancy was diagnosed on D28. Pregnancy rate was not different among groups (C, n = 7/12; E2, n = 5/10; EB, n = 5/10). More (P < 0.05) heifers had a CV-identified prominent PGFM pulse (peak of > 100 pg/mL) in E2 group (6/10) than in EB (1/10) and C (0/12) groups. Hourly concentration of PGFM for Hours 0 to 8 showed significant effects of group and hour and an interaction of group by hour but did not show an interaction of group or hour with pregnancy status. In preliminary post-hoc analyses, PGFM concentrations during Hours 0 to 8 and pulse characteristics were analyzed within each pregnancy status. For the non-pregnant heifers, a group-by-hour interaction was detected tentatively indicating an increase (P < 0.005) in PGFM concentrations in E2 group from Hours 4 to 6 and in EB group at Hours 5 and 6. Maximum PGFM concentration during Hours 0 to 8 did not differ (P > 0.1) between E2 (124 ± 23) and EB (110 ± 30) groups, but was greater (P < 0.05) in each group than in C (32 ± 3). Furthermore, PGFM concentrations of pulses at the peak, amplitude, and area under pulse curve (pg/mL/h) were greater (P < 0.05) in E2 group than in C group whereas the EB group did not differ (P > 0.1) from the other groups. For pregnant heifers, no effects of group, hour, or their interaction were detected in PGFM concentrations during the hourly sessions, except that maximum PGFM concentration was greater (P < 0.05) in E2 than in EB and C groups. In addition, the number of prominent pulses was greater in E2 group than in Control or EB groups. In conclusion, PGFM increased earlier and in greater concentration combined for bred-non-pregnant and pregnant heifers treated 14 days after TAI with 1 mg E2 plus 9 mg P4 than with 1 mg EB. Tentatively, a positive effect for each of E2 and EB on PGFM concentrations was attenuated in pregnant heifers.

Early resynchronization of follicular wave emergence among Nelore cattle using injectable and intravaginal progesterone for three timed artificial inseminations

Follicular dynamics and pregnancy per AI (P/AI) of cattle submitted to resynchronization 13 d after TAI using a progesterone (P₄) insert and supplementary injectable progesterone (iP₄) were determined. There was synchronization of ovulation timing imposed (Day 0 = expected estrus; Experiment 1). On Day 13, animals were assigned to: control (only P₄ insert; 15 cows and 13 heifers) and iP4 (P₄ insert+100 mg iP₄; 13 cows and 12 heifers) groups, and submitted to daily ovarian ultrasonography and blood collection (Day 13 to Day 22). In Experiment 2, 760 suckled cows and 498 heifers were submitted to a TAI on Day 0 and assigned into control and iP4 groups on Day 13. In animals with luteolysis on Day 22, there was a second TAI on Day 24, and on Day 37 were subjected to the opposite treatments as imposed in first resynchronization procedure. On Day 37, there was pregnancy diagnosis in animals with functional CL. The third TAI was performed on Day 48. Day of follicular wave emergence did not differ between groups and parities. Dominant follicles were larger in cows than heifers, and in animals of the control group on Day 24. Greater P₄ concentrations were detected on Day 14 and Day 15 in the iP₄-treated animals. Luteolysis occurred earlier in cows than heifers. Overall P/AI percentage as a result of second and third TAIs, regardless of parity, was greater in iP₄-treated animals. In conclusion, females treated with a supplementary iP₄ had a greater plasma P₄ concentration and P/AI, but there was no effect of iP₄ treatment on synchrony of timing of follicular wave.

Timing of early resynchronization protocols affects subsequent pregnancy outcome in dairy cows

The aim of this study was to evaluate the outcomes of an early resynchronization protocol (Resynch) initiated at different timepoints after timed artificial insemination (TAI) and with unknown pregnancy status. Holstein cows (n = 164) were submitted to the following TAI protocol: D0, insertion of an intravaginal progesterone (P4) device and 2 mg im estradiol benzoate (EB); D8, removal of P4 device and treatment with 0.5 mg im sodium cloprostenol (PGF); D9, 0.1 mg im Lecirelin (LEC); and D10, TAI1. Cows were then randomly assigned to Resynch protocols starting either on day 20 (Resynch20D, n = 82) or 25 after TAI1 (Resynch25D, n = 82) with the insertion of a new P4 device and EB treatment. In both groups, P4 device was removed on day 8 after the beginning of Resynch, the same day of pregnancy diagnosis by ultrasonography. In pregnant cows there was no further action. Non-pregnant cows were treated with 0.5 mg im PGF, had a blood sample collected for serum P4 analysis and we measured and recorded the size of the largest follicle and the presence or absence of a corpus luteum (CL). One day later, cows were treated with 0.1 mg im LEC and TAI2 occurred 12-14 h later. The diameter of the largest follicle and serum P4 were compared between groups by ANOVA for the main effects of treatment, presence of a CL, and their interaction, whereas pregnancy per artificial insemination (P/AI) and the percentage of cows with a CL on the day of ultrasonography were analyzed using the Chi-square test. Follicle diameter on day 8 of Resynch was greater for cows in the Resynch20D group compared with Resynch25D (15.9 ± 3.9 vs 12.2 ± 2.5 mm, respectively; P = 0.046). The Resynch25D group had a greater percentage of cows with a CL (51.9 vs 18.9%, respectively; P = 0.0008) and higher serum P4 (2.8 ± 1.1 vs 1.7 ± 0.8 ng/mL; P = 0.041) at the end of the protocol compared with Resynch20D. P/AI at TAI1 was 35.4 and 36.6% (P > 0.10) for cows enrolled in Resynch20D and Resynch25D groups, respectively. P/AI to TAI2, after Resynch protocols, was greater in Resynch25D than Resynch20D (44.2 vs 22.6%, respectively; P < 0.05). In conclusion, starting an early resynchronization protocol 25 days after TAI increases P/AI compared with starting 20 days after TAI, and this was associated with a presumed greater proportion of cows with a functional CL at the moment of P4 device removal.

New approaches to diagnose and target reproductive failure in cattle

Reproductive failure and pregnancy loss in cattle are some of the largest economic burdens to cattle producers and one of most perplexing factors influencing management decisions. Pregnancy loss may occur at any point during gestation with the largest percentage of loss occurring in the first 30 days and, subsequently, decreasing as the pregnancy progresses. Losses may be attributed to numerous factors, predisposed issues or environmental conditions such as nutritional stressors or disease. From a research perspective, determining the exact causes of pregnancy loss or embryonic mortality in cattle have been difficult, due to limitations of accurately determining early gestation pregnancy status. Until methods that precisely determine embryo success early in gestation are available, our understanding of in vivo pregnancy loss will lack clarity necessary to develop management strategies to decrease such loss. In this review, we will briefly discuss the pivotal periods of pregnancy loss affecting beef and dairy cattle, methods and technologies to determine pregnancy status and embryo viability and potential opportunities to decrease reproductive failure.

Applied use of interferon-tau stimulated genes expression in polymorphonuclear cells to detect pregnancy compared to other early predictors in beef cattle

We aimed to evaluate the accuracy of Interferon-tau stimulated genes (ISG) abundance in peripheral blood polymorphonuclear cells (PMNs) on D20 after fixed-time artificial insemination (FTAI; D0) as a pregnancy diagnosis method against CL evaluation by Doppler ultrasonography and progesterone (P4) concentrations on D20, as well as Pregnancy Associated Glycoproteins (PAG) concentrations on D25. Additionally, we evaluated the potential of ISG abundance in PMNs as pregnancy loss predictors. Nelore heifers (n = 103) and cows (n = 144) underwent estrous synchronization and were artificially inseminated on D0. Pregnancy was diagnosed by B-mode ultrasonography on D30 and D70, and after the final diagnosis, females were classified in four groups: Pregnant; Non-pregnant; Functional CL on D20 but non-pregnant (CL-NP) and Pregnancy loss between D30 and D70 (PL). After determining cutoff values, the Sensitivity (SE), Specificity (SP), Positive Predictive Value (PPV), Negative Predictive Value (NPV) and Accuracy (ACC) were determined for each method. All methods were classified as significant (P < 0.05) predictors of pregnancy. Both ISG expression and PAG concentrations were greater (P < 0.05) in pregnant females than in non-pregnant and CL-NP females but did not differ (P > 0.05) from the PL group. ISG15 expression was greater (P < 0.05) in heifers than in cows, but this difference was not found in OAS1 expression and PAG concentrations. All the methods evaluated were proven to be adequate predictors of pregnancy, but greater accuracies were obtained through PAG concentrations and Doppler-US, due to the decreased number of false positive and false negative results.