Short communication: Field fertility in Holstein bulls: Can type of breeding strategy (artificial insemination following estrus versus timed artificial insemination) alter service sire fertility?

The aim of this study was to compare pregnancy per artificial insemination (P/AI) from service sires used on artificial insemination after estrus detection (EAI) or timed artificial insemination (TAI) breedings. Confirmed artificial insemination outcome records from 3 national data centers were merged and used as a data source. Criteria edits were herd's overall P/AI within 20 and 60%, a minimum of 30 breedings reported per herd-year, service sires that were used in at least 10 different herds with no more than 40% of the breedings performed in a single herd, breeding records from lactating Holstein cows receiving their first to fifth postpartum breedings occurring within 45 to 375 d in milk, and cows with 1 to 5 lactations producing a minimum of 6,804 kg. Initially 1,142,859 breeding records were available for analysis. After editing, a subset of the data (n=857,539) was used to classify breeding codes into either EAI or TAI based on weekly insemination profile in each individual herd. The procedure HPMIXED of SAS was used and took into account effects of state, farm, cow identification, breeding month, year, parity, days in milk at breeding, and service sire. This model was used independently for the 2 types osires f breeding codes (EAI vs. TAI), and service sire P/AI rankings within each breeding code were performed for sires with >700 breedings (94 sires) and for with >1,000 breedings (n=56 sires) following both EAI and TAI. Correlation for service sire fertility rankings following EAI and TAI was performed with the PROC CORR of SAS. Service sire P/AI rankings produced with EAI and TAI were 0.81 (for sires with >700 breedings) and 0.84 (for sires with >1,000 breedings). In addition, important changes occurred in service sire P/AI ranking to EAI and TAI for sires with less than 10,000 recorded artificial inseminations. In conclusion, the type of breeding strategy (EAI or TAI) was associated with some changes in service sire P/AI ranking, but ranking changes declined as number of breedings per service sire increased. Future randomized studies need to explore whether changes in P/AI ranking to EAI versus TAI are due to specific semen characteristics.

Anti-Mullerian hormone concentration and antral ovarian follicle population in Murrah heifers compared to Holstein and Gyr kept under the same management.

This study was performed to evaluate plasma concentrations of anti-Mullerian hormone (AMH) and the ovarian antral follicle population (AFP) in different genetic groups. Cyclic heifers (13 Bubalus bubalis [Murrah]; 15 Bos taurus [Holstein] and 10 Bos indicus [Gyr]) were maintained under the same management and were synchronized with two doses of 150 µg IM d-cloprostenol administered 14 days apart. After the second d-cloprostenol treatment, heifers had their ovaries scanned daily by ultrasound to define the day of ovulation. On the same day, the AFP was determined and a plasma sample was collected to measure AMH. Murrah heifers had less AFP (25.6 ± 2.1 follicles; p = 0.01) and plasma AMH concentration (0.18 ± 0.03 ng/ml; p < 0.001) than Gyr (60.0 ± 12.2 follicles and 0.60 ± 0.12 ng/ml of AMH); however, data were similar when compared to Holstein (35.9 ± 6.8 follicles and 0.24 ± 0.06 ng/ml of AMH) heifers. Regardless of genetic background, there was a positive relationship between the AFP and plasmatic AMH concentration (Murrah [r = 0.62; p < 0.01], Holstein [r = 0.66; p < 0.001] and Gyr [r = 0.88; p < 0.001]). Also, when heifers were classified according to high- or low-AMH concentration based on the average within each genetic group, high-AMH heifers had greater (p < 0.0001) AFP than low-AMH heifers. In conclusion, both Murrah and Holstein heifers presented lower plasma AMH concentration and AFP when compared to Gyr.

Plasma antimullerian hormone as a predictor of ovarian antral follicular population in Bos indicus (Nelore) and Bos taurus (Holstein) heifers.

In Bos taurus cattle, antimullerian hormone (AMH) has been demonstrated to have a high degree of correlation with ovarian antral follicle count and the number of healthy follicles and oocytes. To document the correlation between the plasma concentration of AMH and follicular number in Bos indicus and Bos taurus heifers, Nelore (Bos indicus, n = 16) and Holstein heifers (Bos taurus, n = 16) had their ovarian follicular waves synchronized. After synchronization, ovarian antral follicular population (AFP) was evaluated three times at 60-day (d) intervals (T-120 d, 120 days before plasma AMH determination; T-60 d, 60 days before; and T0, at the time of plasma AMH determination). The plasma AMH concentration was positively correlated with the number of ovarian follicles on the day of the follicular wave emergence in Bos indicus (Nelore) and Bos taurus (Holstein) heifers at each evaluation time (p < 0.05). The AFP was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.05). Similarly, the AMH concentration was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.0001). When heifers were classified as to present high or low AFP according to the mean of the AFP within each genetic group, high-AFP heifers presented a greater (p < 0.0001) AMH concentration than low-AFP heifers, regardless of the genetic group. In conclusion, the AFP is positively correlated with plasma AMH concentration in both Bos indicus (Nelore) and Bos taurus (Holstein) heifers. Furthermore, Bos indicus (Nelore) heifers presented both greater plasma AMH concentrations and AFP than Bos taurus (Holstein) heifers.

Hepatic mRNA expression of enzymes associated with progesterone metabolism and its impact on ovarian and endocrine responses in Nelore (Bos indicus) and Holstein (Bos taurus) heifers with differing feed intakes.

The aim of this study was to evaluate circulating progesterone concentration (P4), LH pulsatility and ovarian follicular dynamics in Nelore (B. indicus) and Holstein (B. taurus) heifers under high (HDMI) and low (LDMI) dry matter/energy intakes. In addition, the effects of dry matter/energy intake and breed on hepatic expression of six genes associated with P4 metabolism (AKR1C4, AKR1D1, CYP3A4, CYP2C19, SRD5A1, and SRD5A3) was evaluated. Heifers received an intravaginal P4 device (1 g), 2 mg of estradiol benzoate (EB) i.m. and 500 µg of PGF2α at the begging of the synchronization protocol (D0). Eight days later, the P4 device was removed and all heifers received 1 mg of EB 24h later. Regardless of dry matter/energy intake, the number of recruited follicles was greater in Nelore than in Holstein heifers. In contrast, the maximum diameter of the dominant follicle was greater in Holstein than in Nelore heifers. Circulating P4 concentrations were greater in Nelore than in Holstein from D2 to D9, and in heifers receiving LDMI than those receiving HDMI from D1 to D8 of hormonal protocol. In addition, Holstein heifers had greater LH pulsatility and area under the curve of LH peaks compared to Nelore heifers. However, no effects were observed for LH values between feed intake levels. Interestingly, Holstein heifers had higher expression of SRD5A1, AKR1C4, AKR1D1 than Nelore heifers; whereas, for Nelore heifers, only the expression of CYP3A4 was higher compared to Holstein heifers. In conclusion, there are important differences in the follicular dynamics, circulating P4 and LH pulsatility concentrations that need to be considered during synchronization protocols for Nelore and Holstein breeds. More importantly, these differences appear to be at least partially modulated by the level of feed intake and the contrasting enzyme system in the liver involved with P4 metabolism between these cattle breeds.

Supplemental progesterone induces temporal changes in luteal development and endometrial transcription in beef cattle.

Long-acting injectable progesterone (iP4) supplementation during early diestrus is a strategy to increase conception rates in cow-calf beef operations. However, iP4 treatment causes early functional and structural regression of the corpus luteum (CL) in a proportion of iP4-treated animals, resulting in pregnancy loss. The hypothesis evaluated was that iP4 accelerates downregulation of sex-steroid receptors (PGR, ESR1, ESR2) during early to mid-diestrus and the upregulation of genes controlling PGF2α secretion (OXTR, PTGS2, AKR1B1) during late diestrus in the endometrium. Ovulations of cyclic, multiparous Nelore (Bos indicus) cows were synchronized, and cows were divided to receive placebo or 300 mg iP4 3 d postovulation (D3). Growth and vascularization of luteal tissue were evaluated by ultrasonography. Blood samples were collected from 3 d postovulation to 3 d after luteolysis, and P4 plasma concentrations were measured by radioimmunoassay. On days 3, 5, 7, 9, 11, 13, and 16 luminal endometrial samples were taken using a cytologic brush. Transcript abundance was measured by qPCR. Structural luteolysis occurred 3 d earlier in cows receiving iP4 compared to the control group. Analyzing only cows that received iP4, those that presented early luteolysis (ie, ≤ D16) showed a decrease in CL area and P4 concentration after D5, compared to the control group. Cows that presented early luteolysis showed a reduced abundance of transcripts on D5 for the ESR2 gene and a greater abundance of transcripts for OXTR and ESR1 on D16, compared to cows that did not present early luteolysis. The iP4-induced early luteolysis can be explained by two nonexclusive possibilities: the activation of uterine mechanisms that trigger early secretion of endometrial PGF pulses and the formation of a subfunctional CL that is prone to early regression.

Profile of LH release in response to intramuscular treatment with kisspeptin in Bos indicus and Bos taurus prepubertal heifers.

The main objective of this study was to evaluate the effect of intramuscular (I.M.) administration of different doses of kisspeptin (Kp) on the pattern of luteinizing hormone (LH) release in Bos taurus and Bos indicus prepubertal heifers. Holstein heifers weighing 215.1 ±â€¯38.6 kg (n = 24; aged 5-8 mo) and Gyr heifers weighing 215.4 ±â€¯31.4 kg (n = 24; aged 6-10 mo) were enrolled in this study. The animals were confirmed as non-cyclical by absence of a corpus luteum (CL) as determined by ultrasound scanning of the ovaries and low circulating P4 concentrations (<1.0 ng/mL) evaluated at a 10-day interval (on day -10 and day 0). For each genetic group, heifers were randomly assigned to one of four treatments: Kp at 2.5 µg/kg body weight (Kp2.5), Kp at 5.0 µg/kg (Kp5), Kp at 10 µg/kg (Kp10), or gonadotropin-releasing hormone (GnRH) agonist (0.01 mg of buserelin acetate per heifer), all administered by I.M. injection. All animals responded to the treatments with an LH surge (P < 0.01). There was an effect of breed (P < 0.01) on induced LH release, with Holstein heifers having a greater area under the curve for LH (AUC; P < 0.01) and greater LH peak amplitude (P < 0.01) than Gyr heifers. Nevertheless, greater AUC for LH occurred in Kp10 heifers for both breeds. There was no effect of breed on LH AUC or LH peak amplitude after GnRH agonist treatment. For both breeds, heifers treated with Kp displayed an earlier (P < 0.01) LH peak with a reduced amplitude of the LH peak (P < 0.01) and reduced LH AUC (P < 0.01) compared to heifers treated with GnRH agonist. Thus, both zebu and taurus immature heifers treated with I.M. Kp injection responded with a rapid and dose-dependent LH surge, although even large doses of the native Kp-10 did not mimic the magnitude or duration of the LH surge produced by the GnRH agonist. The early onset of the LH surge after Kp treatment and the short duration suggest that the effects of Kp were likely due to pituitary rather than hypothalamic action. Finally, there seems to be a greater responsiveness to Kp in Bos taurus than in Bos indicus prepubertal heifers, although LH release after GnRH agonist treatment was similar for the two breeds.

Exacerbated conceptus signaling does not favor establishment of pregnancy in beef cattle.

BACKGROUND: Insufficient production of anti-luteolytic signals by the pre-attachment embryo is considered a major cause of pregnancy failure in cattle. We tested the hypothesis that transfer of multiple blastocysts (n = 5/recipient) and progesterone (P4) supplementation amplify anti-luteolytic signaling and reduce embryonic losses in beef cattle. Cows detected in estrus (D0; n = 104) were assigned randomly to receive 150 mg of injectable long-acting P4 (iP4) or vehicle (non-iP4) on D4 and transcervical transfer of none or five, grade 1, not-frozen, in vitro-produced blastocysts, on D7. Luteal development and time of structural luteolysis were monitored by ultrasonography. Plasma P4 concentrations were determined on D4, D5 and D7, and daily between D14 and D20. Conceptus signaling was monitored by transcript abundance of interferon-stimulated gene 15 (ISG15) in peripheral blood mononuclear cells isolated on D14, D16, D18 and D20. Early embryonic mortality (EEM) was defined as the absence of ISG15 mRNA upregulation over time and/or luteal regression up to D20. Late embryonic mortality (LEM) was defined as the absence of a conceptus with a heartbeat on pregnancy diagnosis at D30 (PD30) after observing upregulation of ISG15 mRNA and extension of luteal lifespan. Pregnant cows presented conceptuses with heartbeat at PD30. RESULTS: On D5, iP4-treated cows had P4 concentrations 2.07-fold greater than non-iP4 treated (P < 0.001). On D7, P4 concentrations were similar. Pregnant and LEM animals showed a progressive increase in the abundance of ISG15 from D14 to D20. iP4-treated cows detected pregnant at PD30 had 1.53-fold greater abundance of ISG15 mRNA between D14 and D20 than non-iP4 treated cows (P = 0.05). iP4 doubled the frequency of EEM while it did not affect LEM. At PD30, embryonic survival was 37.0% vs. 55.6% for iP4-treated vs. control cows. Majority of pregnant cows (71%) presented only a single viable embryo. CONCLUSIONS: A substantial proportion of cows had EEM (31%) and LEM (20%) even after transferring multiple blastocysts. This argues that mortality was due to poor uterine receptivity that could not be reversed by supplemental P4 or overcome by transferring multiple blastocysts. Further, a given uterine environment was not necessarily adequate to all embryos.

The effect of circulating progesterone on magnitude of the GnRH-induced LH surge: Are there any differences between Bos indicus and Bos taurus heifers?

This study evaluated the effects of differing circulating progesterone (P4) levels on the luteinizing hormone (LH) surge profile following treatment with gonadotropin releasing hormone (GnRH) in B. indicus (Nelore, n = 13) and B. taurus (Holstein, n = 16) heifers. All heifers were synchronized with a hormonal protocol to induce either a Low or High circulating P4 environment at the time of GnRH treatment. Heifers were randomly assigned to a 2 × 2 factorial design composed by two genetic groups (B. indicus and B. taurus) and two levels of circulating P4 concentrations (Low or High). Blood samples were collected every 30 min from -30 to 210 min and at 270 min after GnRH treatment. As expected, mean P4 concentration was greater for cows in the High than in the Low P4 group (P = 0.0008) and in Bos indicus than in Bos taurus heifers (P = 0.06). Despite genetic group, the area under the curve of LH release was greater in the Low-P4 than in High-P4 concentration group (P < 0.0001). Interestingly, it appears that High P4 concentrations had a more pronounced effect on LH peak in B. indicus than in B. taurus heifers, as indicated by the interaction (P = 0.01) between genetic group and P4 levels. In conclusion, circulating P4 concentration have a great impact on the GnRH-induced LH surge of both B. indicus and B. taurus heifers, but it does not explain the much lower LH peak in B. indicus with low circulating P4. Thus, more studies are essential to uncover some of the underlying physiological factors other than circulating P4 that are limiting LH release following a GnRH treatment in B. indicus cattle.

Beef donor cows with high number of retrieved COC produce more in vitro embryos compared with cows with low number of COC after repeated ovum pick-up sessions.

The aim of the present study was to evaluate whether repeated ovum pick-up (OPU) procedures may affect the efficiency of OPU programs for in vitro embryo production (IVEP) in Bos indicus (Nelore) donors. In addition, the repeatability (r) efficiency of IVEP was also assessed. Data available were from 432 OPU-IVEP sessions that were performed at random stages of the estrous cycle in 36 cycling, nonlactating Nelore donors. Semen from three Nelore bulls was used for the IVF. Donors were submitted to 12 consecutive OPU procedures, with an interval of approximately 30 days between sessions. Data were analyzed as repeated measures using the GLIMMIX procedure of SAS 9.3. Cows yielding ≥15 COCs were defined as "high" COCs and cows with less than 15 COCs were defined as "low" COCs donors. The number of COCs retrieved decreased over time in donors classified with high COCs and remained fairly steady in cows with low COCs at the beginning of the program (Psession*COC retrieved groups = 0.02). Moreover, the number of COCs retrieved (P < 0.0001), and number of blastocysts produced per OPU (P = 0.001) was greater for the high COCs donors compared with the low COCs category, and these results were consistent across OPU sessions. Interestingly, there was no effect of COCs category on the rate of blastocyst development (P = 0.83). In addition, number of blastocysts produced were not affected by repeated OPU (P = 0.37) and interactions between time and COC category (P = 0.72). Similarly, blastocyst rate was not affected by repeated OPU (P = 0.21) and interactions between time and COC category (P = 0.58). Despite of COC category of the donor cows, repeatability was high for the number of COCs retrieved (r = 0.81), number of blastocysts produced per OPU (r = 0.79), and blastocyst rate (0.69). In conclusion, overall numbers of COCs decreased over time in donors classified as having high COCs. However, cumulative amounts of produced blastocysts were greater in donors with high COCs. More importantly, high repeatability was observed in terms of IVEP efficiency. Therefore, IVEP programs can be significantly improved with more aggressive selection toward donors with greater numbers of COCs.

Ovarian follicular growth suppression by long-term treatment with a GnRH agonist and impact on small follicle number, oocyte yield, and in vitro embryo production in Zebu beef cows.

The aim of the present study was to evaluate small follicle number, oocyte yield, and in vitro embryo production (IVEP) in Zebu beef cows treated long term with a GnRH agonist to suppress ovarian follicular growth. Nelore (Bos indicus) cows (n = 20) showing regular estrous cycles were randomly assigned to one of two groups: control (n = 10, placebo ear implant without a GnRH agonist); GnRH agonist (n = 10, GnRH agonist ear implant containing 9.4-mg deslorelin). All cows underwent an ovum pick-up (OPU) session 14 days (Day 14) before the start of treatments (Day 0) followed by seven OPU-IVEP procedures at 30-day intervals (Days 0, 30, 60, 90, 120, 150, and 180). Semen from a single batch of a previously tested bull was used for all the IVEP. Cows treated with agonist reported a decrease over time in the proportion of animals with a (CL; P ≤ 0.05) and large follicles (>10 mm, P ≤ 0.05). These cows had a lesser number of medium + large follicles (>5 mm; 1.74 ± 0.5 vs. 4.13 ± 0.5; P ≤ 0.05), greater number of small follicles (2-5 mm; 44.3 ± 2.8 vs. 30.8 ± 1.8; P ≤ 0.05), greater yield of cumulus-oocyte complexes (COCs; 21.0 ± 2.3 vs. 15.6 ± 1.9; P ≤ 0.05), greater proportion of COCs cultured (79.2 vs. 73.9%; P ≤ 0.05), COCs cleaved (10.6 ± 1.5 vs. 6.8 ± 1.1, P ≤ 0.05), and cleaved rate (52.8 vs. 44.3%; P ≤ 0.05) compared with control cows. The number (3.4 ± 0.7 vs. 3.0 ± 0.6; P > 0.05) and proportion (16.5 vs. 19.1%; P > 0.05) of blastocysts produced were similar between agonist and control cows, respectively. The study has shown that Zebu beef cows treated long term with a GnRH agonist had follicular growth restricted to small follicles. This did not compromise the ability of oocytes to undergo IVF and embryonic development.

Plasma anti-Müllerian hormone as a predictive endocrine marker to select Bos taurus (Holstein) and Bos indicus (Nelore) calves for in vitro embryo production.

This study evaluated the association between plasma anti-Müllerian hormone (AMH) concentrations and in vitro embryo production in Bos indicus (Nelore; experiment 1) and Bos taurus (Holstein; experiment 2) calves superstimulated or not with 140 mg of porcine follicle-stimulating hormone (pFSH; 4 decreasing doses twice daily). Oocytes were recovered from calves aged 2 to 4 mo after receiving gonadotropin stimulation (Nelore, n = 15; Holstein, n = 12) or not (Nelore, n = 15; Holstein, n = 12). Cycling heifers formed a positive control group (n = 15 for Nelore [aged 18-24 mo], n = 10 for Holstein [aged 14-16 mo]). All the calves underwent laparoscopic ovum pickup, and cycling heifers underwent a regular transvaginal ultrasound-guided ovum pickup for oocyte recovery. Immediately before oocyte retrieval, blood samples were taken for subsequent AMH determination (ng/mL). Regardless of the genetic group, calves that received pFSH (3.6 ± 1.1 in Nelore and 4.6 ± 1.2 in Holstein) or did not receive pFSH (3.2 ± 1.0 in Nelore and 2.5 ± 0.8 in Holstein) had greater plasma AMH concentrations (P = 0.01 in Nelore and P = 0.003 in Holstein) than cycling heifers (1.1 ± 0.2 in Nelore and 0.6 ± 0.07 in Holstein). AMH concentrations in calves with or without pFSH were similar in both genetic groups (3.6 ± 1.1 vs 3.2 ± 1.0 in Nelore; 4.6 ± 1.2 vs 2.5 ± 0.8 in Holstein). In calves, positive correlations were observed between plasma AMH concentrations and the numbers of follicles >2 mm (r = 0.86, P < 0.0001 in Nelore; r = 0.78, P < 0.0001 in Holstein), cumulus-oocyte complexes (COCs) retrieved (r = 0.91, P < 0.0001 in Nelore; r = 0.82, P < 0.0001 in Holstein), COCs cultured (r = 0.71, P < 0.0001 in Nelore; r = 0.79, P < 0.0001 in Holstein), and blastocysts produced (r = 0.62, P = 0.0003 in Nelore; r = 0.58, P = 0.009 in Holstein), and these results were independent of pFSH treatment. In conclusion, calves had greater plasma AMH concentrations than cycling heifers. In addition, treatment with pFSH did not influence AMH concentrations in calves, regardless of the genetic group. More importantly, plasma AMH concentrations were positively correlated with the antral follicle population and the number of COCs retrieved, COCs cultured, and blastocysts produced in B indicus and B taurus calves. Therefore, AMH is a promising tool for selecting oocyte donor calves to maximize results during in vitro embryo production.

Paradoxical effects of bovine somatotropin treatment on the ovarian follicular population and in vitro embryo production of lactating buffalo donors submitted to ovum pick-up.

The aim of the present study was to evaluate the effect of bovine somatotropin (bST; 500mg) administration on lactating buffalo donors submitted to two different ovum pick-up (OPU) and in vitro embryo production schemes with a 7 or 14d intersession OPU interval. A total of 16 lactating buffalo cows were randomly assigned into one of four experimental groups according to the bST treatment (bST or No-bST) and the OPU intersession interval (7 or 14d) in a 2×2 factorial design (16 weeks of OPU sessions). The females submitted to OPU every 14d had a larger (P<0.001) number of ovarian follicles suitable for puncture (15.6±0.7 vs. 12.8±0.4) and an increased (P=0.004) number of cumulus-oocyte complexes (COCs) recovered (10.0±0.5 vs. 8.5±0.3) compared to the 7d interval group. However, a 7 or 14d interval between OPU sessions had no effect (P=0.34) on the number of blastocysts produced per OPU (1.0±0.1 vs. 1.3±0.2, respectively). In addition, bST treatment increased (P<0.001) the number of ovarian follicles suitable for puncture (15.3±0.5 vs. 12.1±0.4) but reduced the percentage (18.9% vs. 10.9%; P=0.009) and the number (1.4±0.2 vs. 0.8±0.1; P=0.003) of blastocysts produced per OPU session compared with the non-bST-treated buffaloes. In conclusion, the 14d interval between OPU sessions and bST treatment efficiently increased the number of ovarian follicles suitable for puncture. However, the OPU session interval had no effect on embryo production, and bST treatment reduced the in vitro blastocyst outcomes in lactating buffalo donors.

Prostaglandin treatment at the onset of norgestomet and estradiol-based synchronization protocols did not alter the ovarian follicular dynamics or pregnancy per timed artificial insemination in cyclic Bos indicus heifers.

The aim of the present study was to evaluate the effects of the PGF2α treatment given at the onset of a synchronization of ovulation protocol using a norgestomet (NORG) ear implant on ovarian follicular dynamics (Experiment 1) and pregnancy per AI (P/AI; Experiment 2) in cyclic (CL present) Bos indicus heifers. In Experiment 1, a total of 46 heifers were presynchronized using two consecutive doses of PGF2α 12 days apart. At first day of the synchronization protocol the heifers received implants containing 3mg of NORG and 2 mg of estradiol benzoate (EB). At the same time, heifers were randomly assigned to receive 150 mg of D-cloprostenol (n=23; PGF2α) or no additional treatment (n=23; Control). When the ear implants were removed 8 days later, all heifers received a PGF2α treatment and 1 mg of EB was given 24 h later. The follicular diameter and interval to ovulation were determined by transrectal ultrasonography. No effects of PGF2α treatment on the diameter of the largest follicle present were observed at implant removal (PGF2α=9.8±0.4 vs. Control=10.0±0.3 mm; P=0.73) or after 24 h (PGF2α=11.1±0.4 vs. Control=11.0±0.4 mm; P=0.83). No differences in the time of ovulation after ear implant removal (PGF2α=70.8±1.2 vs. Control=73.3±0.9 h; P=0.10) or in the ovulation rate (PGF2α=87.0 vs. Control=82.6%; P=0.64) between treatments were observed. In Experiment 2, 280 cyclic heifers were synchronized using the same experimental design described above (PGF2α; n=143 and Control; n=137), at random day of the estrous cycle. All heifers received 300 IU of equine chorionic gonadotropin (eCG) and 0.5 mg of estradiol cypionate (as ovulatory stimulus) when the NORG ear implants were removed. Timed artificial insemination (TAI) was performed 48 h after implant removal and the pregnancy diagnosis was conducted 30 days later. No effects on the P/AI due to PGF2α treatment were observed (PGF2α=51.7 vs. Control=57.7%; P=0.29). In conclusion, PGF2α treatment at the onset of NORG-based protocols for the synchronization of ovulation did not alter the ovarian follicular responses or the P/AI in cyclic Bos indicus beef heifers synchronized for TAI.

Plasma anti-mullerian hormone: an endocrine marker for in vitro embryo production from Bos taurus and Bos indicus donors.

The aim of this study was to evaluate the association between plasma anti-mullerian hormone (AMH) concentration and in vitro embryo production (IVP) from Bos taurus (Holstein) and Bos indicus (Nelore) donors. A total of 59 Holstein (15 prepubertal heifers aged 8-10 mo, 15 cyclic heifers aged 12-14 mo, 14 lactating cows, and 15 nonlactating cows) and 34 Nelore (12 prepubertal heifers aged 10-11 mo, 10 prepubertal heifers aged 21-23 mo, and 12 cyclic heifers aged 24-26 mo) females were enrolled. All females underwent an ovum pick-up (OPU), without previous synchronization of the follicular wave, and IVP procedure. Immediately before the OPU procedure, blood samples were collected for subsequent AMH determination. A positive correlation was observed between the plasma AMH and number of in vitro embryos produced from Holstein (r = 0.36, P < 0.001) and Nelore (r = 0.50, P = 0.003) donors. For additional analyses, donors within each genotype were classified into 1 of 2 AMH categories (low or high) according to the average AMH concentration for each genotype. The results revealed that females classified as having high AMH presented a greater number of visible aspirated follicles (Holstein: 20.9 ± 1.5 vs 13.6 ± 0.9, P < 0.0001; Nelore: 54.3 ± 6.1 vs 18.6 ± 2.1, P < 0.0001) and a greater number of recovered cumulus-oocyte complexes (Holstein: 17.3 ± 1.5 vs 9.0 ± 0.9, P < 0.0001; Nelore: 45.3 ± 6.4 vs 13.4 ± 1.7, P < 0.0001). However, there was no difference in the blastocyst production rate (Holstein: 20.6% ± 4.0% vs 19.8% ± 4.2%, P = 0.60; Nelore: 33.7% ± 6.5% vs 27.4% ± 5.5%, P = 0.41, high and low AMH, respectively). Moreover, donors classified as having high AMH yielded a greater number of embryos produced per OPU (Holstein: 3.0 ± 0.7; Nelore: 7.0 ± 1.7) compared with those classified as having low AMH (Holstein: 1.2 ± 0.3, P = 0.04; Nelore: 2.2 ± 0.5, P = 0.007). In conclusion, although the plasma AMH concentration did not alter the ability of the cumulus-oocyte complex to reach the blastocyst stage, the AMH concentration in plasma can be an accurate endocrine marker for the in vitro embryo yield from either B. taurus (Holstein) or B. indicus (Nelore) donors. Therefore, AMH is a promising tool to enhance the overall efficiency of OPU-IVP programs in the field as a selective criterion for high embryo producing donors.