Comparison of estradiol benzoate doses for resynchronization of ovulation at 14 days after timed-AI in suckled beef cows

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.

Optimisation of Early Pregnancy Diagnosis and Resynchronisation in Beef Cows

The objectives of this study were (1) to investigate the effects of the preovulatory follicle (POF) size on the accuracy of Doppler-based early pregnancy detection, and (2) to determine whether the removal of PGF2α (PGF) treatment during the resynchronisation protocol would affect fertility in beef cows. In Experiment 1, Nelore suckling cows (n = 224) were enrolled in an estradiol-progesterone-based timed artificial insemination (TAI) protocol. At TAI, cows were separated based on the range of POF diameters, as follows: ≤11.0 mm (n = 50), 11.1-12.9 mm (n = 64), 13.0-14.4 mm (n = 62) and ≥14.5 mm (n = 48). On day 22 after TAI, the corpus luteum (CL) blood flow (CLBF) of all cows was examined by colour Doppler ultrasonography to diagnose nonpregnant cows. The cows with the largest POF had the greatest positive predictive value (88.6%; 31 of 35) and diagnostic accuracy (91.7%; 44 of 48). In Experiment 2, Nelore cows (n = 233) were subjected to the same TAI protocol. Fourteen days after TAI, all cows were started on a resynchronisation protocol. Cows diagnosed as nonpregnant based on CLBF, on day 22, received 0.5 mg estradiol cypionate intramuscular (im) and were assigned to receive either 150 μg of PGF (PGF; n = 50) or 2 mL of saline (control; n = 47). Cows treated with PGF had a P/AI of 30.0% compared with a 48.9% P/AI in controls (p = 0.06). Our findings demonstrate that the POF size affects the accuracy of a CLBF-based early pregnancy diagnosis and that the removal of PGF treatment from the resynchronisation protocol tended to increase P/AI of the second TAI.

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.

Metabolomic evolution of the postpartum dairy cow uterus

High rates of early pregnancy loss are a critical issue in dairy herds, particularly in seasonal, grazing systems. Components of the uterine luminal fluid (ULF), on which the early embryo depends for sustenance and growth, partly determine early pregnancy losses. Here, changes in ULF from early to mid-postpartum in crossbred dairy cows were explored, linking them with divergent embryo development. For this, the uteri of 87 cows at Day 7 of pregnancy at first and third estrus postpartum were flushed to collect ULF. Eighteen metabolites (chiefly organic acids and sugars) significantly varied in abundance across postpartum, indicating a molecular signature of physiological recovery consistent of the upregulation of pyrimidine metabolism and glycerophospholipid metabolism, and downregulation of pentose phosphate and taurine metabolism pathways. Joint pathway analysis of metabolomics data and a previously generated proteomics data set on the same ULF samples suggests key links between postpartum recovery and subsequent successful embryo development. These include upregulation of VEGFA and downregulation of metabolism, NRF2, T-cell receptor, which appear to improve the ULF's capacity of sustaining normal embryo development, and a putative osmo-protectant role of beta-alanine. These relationships should be further investigated to develop tools to detect and reduce early pregnancy loss in dairy cows.

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.