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

Age-specific analysis of anti-müllerian hormone and liver biochemical parameters in freemartin holstein calves and heifers: A pilot study

Freemartinism is the most common congenital anomaly among sexual disorders in dairy cows. This syndrome typically occurs in different-sex twin pregnancies and causes vascular anastomoses to form with the placenta in the early stages of fetal development. The study aims to determine the effectiveness of Anti-müllerian hormone (AMH) levels in calves and heifers of different age groups for diagnostic factors and to investigate the potential consequences of different hormone levels in different age groups on some liver biochemical parameters. The study involved 50 cattle from diverse age categories, divided into the freemartin group (FM Group, n=25) and the control group (C Group, n=25). Both FM and control groups were further divided into early-age (3-5 months), middle-aged (5-9 months), and older-aged groups (9-12 months). Serum AMH levels, along with total protein, albumin, and total cholesterol levels, were measured. While no statistically significant difference in AMH levels was observed in the early-age group (P:0.53), significant differences were determined in the middle (P:0.015) and older-age groups (P:0.01), where the FM group exhibited significantly decreased AMH levels compared to the control group. The evaluation of liver biochemistry revealed a statistically significant difference in total protein levels between the FM and control groups in the older age group (P:0.033). Consequently, it is reasonable to suggest that AMH levels may serve as a valid parameter for diagnosing freemartin syndrome in calves aged older than five months. Conversely, particularly in young calves, no significant differences in liver functionality were observed between freemartin-affected and healthy calves.

Do the blood anti-Müllerian hormone concentrations in young females correlate with the ovarian follicular population later in life in water buffalo?

In this longitudinal study, the anti-Müllerian hormone (AMH) levels in blood were determined in 32 Murrah buffalo females at 8, 10, 12, 16 and 19 months of age when females were synchronized and the antral follicular population (AFP) was estimated. Correlations of AFP to the AMH level at 19 months of age and retrospectively to younger ages were investigated. Then females were split into high and low AFP, and their AMH levels were compared for all ages and tested as predictors of AFP categories. The highest AMH level (p < .05) was detected at 8 months, reducing but not differing (p > .05) at 10, 12 and 16 months then reducing again (p < .05) at 19 months of age. The mean AFP was 17.6 ± 6.3 follicles, and it was positively correlated with AMH in all ages tested. High AFP females had approximately two times more antral follicles than low AFP (p < .05) and their AMH levels were higher (p < .01) than in low AFP ones in all ages. Only at 8 months, AMH levels can be used to precociously detect high AFP heifers (a cut-off point of 464.7 pg/mL; p < .05), while low AFP heifers could be detected by AMH measurements at 8, 10, 12 and 16 months of age (p < .05). We conclude that AMH of buffalo calves correlates with AFP of heifers later in life and depending on the age, its levels could be used to identify future females with low or high AFP.

Effect of food supplementation on in vitro embryo production and growth performance in prepubertal Nelore heifers

In vitro embryos production from prepubertal heifers can help contribute to breeding programs; however, strategies are necessary to increase their embryo production. The aim of this study was to investigate the effects of two nutritional plans on oocyte recovery, embryo production and growth performance of prepubertal Nelore heifers. Thirty-four Nelore heifers with age of 6.5 months were divided into two feeding treatments (NP1 and NP2). The NP1 diets served as the control and NP2 diets were formulated to contain an average of 1.22-fold more energy than NP1. After 3 months of supplementation, the animals underwent follicular aspiration (ovum pick-up, OPU) every 21 d for 3 months and embryos were produced in vitro. Wither height, chest depth, body weight and subcutaneous fat of animals were measured. The number of retrieved and viable oocytes per OPU were 1.49-fold and 1.42-fold greater in NP2 heifers (p = 0.018 and p = 0.049, respectively) than those in NP1 heifers. Heifers administered NP2 produced 29.7% blastocysts, a percentage higher than NP1 animals that produced 24.40% embryos (p < 0.05). Consequently, females in the NP2 treatment showed improved body development. These results indicate a positive effect of a higher energy diet on assisted reproduction and body development in prepubertal heifers.

The oocyte: the key player in the success of assisted reproduction technologies

The ovulation of a mature oocyte at metaphase II of meiosis, with optimal potential to undergo fertilisation by a sperm cell, complete meiosis and sustain the switch to mitotic division, and support early embryo development, involves a protracted and disrupted/delayed series of processes. Many of these are targeted for exploitation in vivo , or recapitulation in vitro , by the livestock industry. Reproductive technologies, including AI, multiple ovulation embryo transfer, ovum pick-up, in vitro embryo production, and oestrus and ovulation synchronisation, offer practitioners and producers the opportunity to produce offspring from genetically valuable dams in much greater numbers than they would normally have in their lifetime, while in vitro oocyte and follicle culture are important platforms for researchers to interrogate the physiological mechanisms driving fertility. The majority of these technologies target the ovarian follicle and the oocyte within; thus, the quality and capability of the recovered oocyte determine the success of the reproductive intervention. Molecular and microscopical technologies have grown exponentially, providing powerful platforms to interrogate the molecular mechanisms which are integral to or affected by ART. The development of the bovine oocyte from its differentiation in the ovary to ovulation is described in the light of its relevance to key aspects of individual interventions, while highlighting the historical timeline.

In vitro and in vivo embryo production efficiency in Flemish and Holstein donor females

The aim of this study was to compare embryo production efficiency in Flemish and Holstein donor females using ovum pick-up and in vitro fertilization (OPU-IVF) or in vivo production (superovulation; SOV) procedures. The study was conducted using a split-plot design, with eight Flemish and eight Holstein non-lactating cycling females. Females were subjected to ten weekly OPU/IVF sessions and/or two SOV/embryo collections sessions at a 63-day interval, for a total of 160 OPU-IVF and 32 SOV sessions. Mean numbers of follicles and corpora lutea, and cumulus-oocyte complex (COC) recovery rates were similar between breeds after the OPU and SOV sessions. However, Flemish donors yielded better quality grade II COCs (301, 41.9%) than Holstein females (609, and 202, 33.1%). Also, cleavage and blastocyst rates, and the total number and the mean number of viable embryos obtained after OPU-IVF were higher in Flemish (49.6% and 11.8%, and 63 and 11.8 per donor, respectively) than in Holstein (32.8% and 7.2%, and 34 and 7.2 per donor, respectively) females. Flemish females were also more efficient in yielding viable embryos after SOV (111, 7.3 per donor) than Holstein (48, 3.3 per donor) females. Overall, Flemish donor females had better responses to OPU-IVF or SOV procedures than Holstein counterparts. Irrespective of the breeds, SOV procedures were more efficient than OPU-IVF in yielding more viable embryos, under the conditions of this study. Both reproductive procedures were useful tools for the genetic conservation of the Flemish cattle breed in Southern Brazil.

Factors Affecting the Efficiency of In Vitro Embryo Production in Prepubertal Mediterranean Water Buffalo

Embryos from prepubertal water buffalo can be produced using laparoscopic ovum pickup (LOPU) and in vitro embryo production (IVEP). However, to date, it is unclear what factors and environmental conditions can affect LOPU-IVEP efficiency in prepubertal animals, especially buffalo. In this study, we explored the impact of season, age and individual variation among female donor animals, as well as the effect of the sire used for in vitro fertilization. Donor animals between 2 and 6 months of age were stimulated using gonadotropins prior to LOPU, which was performed at two-week intervals. Following in vitro maturation and fertilization, the resulting embryos were then cultured to the blastocyst stage until they were either vitrified or transferred into recipient animals. The number of follicles available for aspiration and embryo development rates was stable throughout the year. As animals became older, there was a slight trend for fewer COCs recovered from LOPU and better embryo development. There was a large individual variation in both ovarian response and the developmental competence of oocytes among donors. The bull used for fertilization also had a significant impact on embryo development. Upon embryo transfer, pregnancy rates were not affected by the number of embryos transferred per recipient. The best pregnancy rates were achieved when transferring blastocysts, compared to compact morula or hatched blastocysts. Finally, vitrification had no effect on pregnancy rate compared to fresh embryos.

Predictors of the ovarian superstimulatory response and oocyte collection in prepubertal heifers

The objectives were to investigate the relationships between antral follicle counts and plasma AMH and FSH at the time of follicular wave emergence in prepubertal calves, and to determine the effects of age and duration of gonadotropin treatment on the ovarian superstimulatory response in pre- and post-pubertal heifers. Hereford crossbred prepubertal (Replicate 1 and 2, n = 20) and post-pubertal heifers (Replicates 1, n = 8; Replicate 2, n = 8) were assigned randomly to 2 treatment groups and given FSH for either 4 or 7 d (25 mg pFSH im at 12-h intervals). Prepubertal heifers were first treated at 4 mo and again at 7 mo of age. Blood samples were collected immediately before the first FSH administration, that was initiated 36 h after follicular ablation. An LH treatment (12.5 mg im) was given 12 h after the last FSH injection. Follicular fluid and cumulus-oocyte complexes (COC) were collected 24 h after LH treatment. At wave emergence, the number of follicles ≥1 mm (AFC, 31.1 ± 4.0 vs 16.2 ± 1.8; P < 0.001) and the plasma concentrations of AMH (606.4 ± 90.5 vs 279.6 ± 28.3 pg/mL; P = 0.001) were higher at 4 than at 7 mo of age, while plasma FSH concentrations did not differ between ages. At oocyte collection, a higher number of follicles ≥6 mm were observed in prepubertal calves at 4 mo of age and post-pubertal heifers than in calves at 7 mo of age (32.4 ± 5.4 and 22.0 ± 2.3 vs 14.9 ± 2.0, respectively; P = 0.003). Intrafollicular concentrations of estradiol were lower (23.7 ± 4.5 vs 144.0 ± 29.5 ng/mL; P < 0.0001) and of progesterone tended to be higher (217.5 ± 29.3 vs 157.0 ± 33.9 ng/mL; P = 0.07) in the 7- than in the 4-d groups. A greater number of COC was collected from calves at 4 mo of age and heifers than the 7-mo-old calves (13.4 ± 2.6 and 6.0 ± 1.0 vs 5.8 ± 1.1, respectively; P = 0.008). Overall, the 7-d FSH treatment tended to result in a greater proportion of expanded COC than the 4-d treatment in calves (50.1 ± 7.7 vs 31.9 ± 6.8%; P = 0.07). In summary, there was a positive relationship between AFC and plasma AMH concentrations at the time of wave emergence. A higher AFC was observed in calves at 4- than 7-mo of age, which resulted in greater ovarian response to gonadotropin treatment. Following an exogenous LH stimulus, COC maturation rates were greater in the 7-d than in the 4-d FSH treatment groups, resulting in collection of a higher proportion of fully expanded COC.

Dynamics of the Reproductive Changes and Acquisition of Oocyte Competence in Nelore (Bos taurus indicus) Calves during the Early and Intermediate Prepubertal Periods

The purpose of this study was to characterize the reproductive physiology, oocyte competence, and chromatin compaction in Nelore calves in the early-prepubertal period (EPP) and the intermediate-prepubertal period (IPP). Calves aged 2-5 (EPP) and 8-11 months old (IPP) were assigned to Trial 1 (morpho-physiological-endocrine evaluations, n = 8) or Trial 2 (oocyte donors, n = 8) vs. the respective control groups of cows (n = 8, each). All morphological endpoints, except the antral follicle count, increased from the EPP to the IPP. The EPP LH-FSH plasma concentrations were similar to cows, whereas LH was lower and FSH was higher in the IPP than in cows. . Cows produced more Grade I (12.9% vs. 4.1% and 1.7%) and fewer Grade III COC (30.1% vs. 44.5% and 49.0%) than the EPP and IPP calves, respectively. The IPP calves' oocyte diameter was similar to those from cows but greater than those from EPP females (124.8 ± 8.5 and 126.0 ± 7.5 μm vs. 121.3 ± 7.5 μm, respectively). The expression of the chromatin compaction-related gene HDAC3 was downregulated in calves. The proportion of the blastocyst rate to the controls was lower in EPP than in IPP calves (43.7% vs. 78.7%, respectively). Progressive oocyte competence was found during the prepubertal period, which can help to decide whether to recover oocytes from calves.

Temporal evaluation of follicular dynamics and endocrine patterns of Holstein (Bos taurus), Gir (Bos indicus), and Murrah (Bubalus bubalis) heifers kept under the same nutritional, management and environmental conditions

The objective of the study was to simultaneously compare ovarian follicular dynamics and endocrine parameters of taurine (Holstein; n = 14), zebuine (Gir; n = 5), and bubaline (Murrah; n = 15) heifers kept under the same environmental, nutritional and management conditions. Heifers were synchronized with two PGF treatments 14 days apart. Ovaries of cyclic heifers were scanned daily during two consecutive ovulations and blood samples were collected every 24 h from each animal. No significant difference was found for length of interovulatory interval, however, zebuine heifers presented a greater number of follicular waves, number of antral follicles on day of ovulation, and higher insulin concentration than the other two breeds. Taurine heifers had highest maximal diameter of first wave dominant and ovulatory follicles and CL volume. Taurine and bubaline heifer's dominant follicle of first wave had longer static and regression phases than zebuine heifers. Bubaline heifers presented overall lowest progesterone concentrations and CL volume, but higher IGF1 levels. No difference was observed between taurine and zebuine heifers regarding IGF1 concentration. Despite higher CL volume found in taurine heifers, no difference in mean progesterone concentration was observed between them and zebuine heifers. Insulin and IGF1 concentrations were greater in follicular phase than in luteal phase when breed was not evaluated. After evaluating the three breeds simultaneously, at the same nutritional and management status it is possible to conclude that each genetic group has a specific follicular development and endocrinology of the estrous cycle.

Impact of oocyte donor age and breed on in vitro embryo production in cattle, and relationship of dairy and beef embryo recipients on pregnancy and the subsequent performance of offspring: A review

Genomic selection combined with in vitro embryo production (IVEP) with oocytes from heifer calves provides a powerful technology platform to reduce generation interval and significantly increase the rate of genetic gain in cattle. The ability to obtain oocytes with developmental competence from calves has been recognised for more than 60years. There is renewed interest in the potential of this reproductive technology as the beef and dairy industries seek to identify and multiply animals that satisfy consumer demand for efficient utilisation of natural resources, with minimal environmental impact and high product quality. Heifer calves show a good follicular response to FSH stimulation and oocytes can be recovered by ovum pick-up (OPU). However, the efficiency of OPU/IVEP remains lower for calves compared with peripubertal heifers and cows, in both indicus (Zebu, Bos indicus ) and taurus (Bos taurus ) breeds. Indicus cattle generally have more follicles, yield a greater number of oocytes, and have a better IVEP outcome, compared with taurus cattle. The treatment of prepubertal heifers with bovine somatotrophin (bST) and propylene glycol before OPU/IVEP has yet to show a major improvement in embryo production. Holstein (taurus) dairy heifers derived from different reproductive technologies (AI, MOET, OPU/IVEP) showed a similar age at puberty and first-lactation milk production. OPU/IVEP Holstein embryos transferred to beef or dairy cows likewise yielded heifers with the same performance. The gains in productivity that can be achieved with strategic use of OPU/IVEP in heifer calves make this a relevant and highly important reproductive technology in cattle breeding. Ongoing optimisation of the technology is needed for the potential of OPU/IVEP in young donors to be fully realised.

In Vitro Production of Embryos from Prepubertal Holstein Cattle and Mediterranean Water Buffalo: Problems, Progress and Potential

Laparoscopic ovum pick-up (LOPU) coupled with in vitro embryo production (IVEP) in prepubertal cattle and buffalo accelerates genetic gain. This article reviews LOPU-IVEP technology in prepubertal Holstein Cattle and Mediterranean Water Buffalo. The recent expansion of genomic-assisted selection has renewed interest and demand for prepubertal LOPU-IVEP schemes; however, low blastocyst development rates has constrained its widespread implementation. Here, we present an overview of the current state of the technology, limitations that persist and suggest possible solutions to improve its efficiency, with a focus on gonadotropin stimulations strategies to prime oocytes prior to follicular aspiration, and IVEP procedures promoting growth factor metabolism and limiting oxidative and endoplasmic reticulum stress.

Effect of calfhood nutrition on metabolic hormones, gonadotropins, and estradiol concentrations and on reproductive organ development in beef heifer calves

This study examined the effect of plane of nutrition on the endocrinological regulation of the hypothalamic-pituitary-ovarian (HPO) axis in beef heifer calves during a critical sexual developmental window early in calf hood. Forty Holstein-Friesian × Angus heifers (mean age 19 d, SEM = 0.63) were assigned to a high (HI; ADG 1.2 kg) or moderate (MOD; ADG 0.50 kg) nutritional level from 3 to 21 wk of life. Intake was recorded using an electronic calf feeding system, BW was recorded weekly, and blood samples were collected on the week of age 5, 10, 15, and 20 for metabolite, reproductive, and metabolic hormone determination. At 19 wk of age, on sequential days, an 8-h window bleed was carried out for luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol analysis. To characterize anterior pituitary gland function, an intravenous GnRH challenge was conducted (19 wk of age). Blood was collected via a jugular catheter every 15 min for 135 min for the analysis of LH, FSH, and estradiol. Calves were subsequently euthanized at 21 wk of age; the anterior pituitary, metabolic organs, and reproductive tract were weighed, and ovarian surface follicular numbers and oocytes recovered were recorded. Mean ADG was 1.18 and 0.50 kg for HI and MOD, respectively, resulting in a 76.6-kg difference in BW (P < 0.001). Blood insulin, glucose, and IGF-1 concentrations were greater (P < 0.001) for HI compared with MOD. There was a diet × time interaction for leptin (P < 0.01); concentrations were greater in HI compared with MOD at 20 wk of age with no difference between treatments before this. Dietary treatment did not alter the concentrations of adiponectin or anti-mullerian hormone. There was a diet × time interaction for FSH, whereby MOD had greater concentrations than HI at 10, 15, and 20, but not at 5 wk of age. Over the duration of an 8-h window bleed (19 wk of age), serum concentrations of LH, LH pulse frequency, and LH pulse amplitude were unaffected by treatment, whereas FSH (0.23 vs. 0.43 ng/mL) and estradiol (0.53 vs. 0.38 ng/mL) concentrations were less than and greater, respectively, for HI than MOD (P < 0.05). Likewise, following a GnRH challenge, the area under the curve analysis revealed greater (P < 0.01) estradiol and lesser (P < 0.01) FSH concentrations in calves on the HI relative to MOD diet, whereas concentrations of LH were unaffected (P = 0.26) between treatments. Ovarian surface follicle numbers were greater (P < 0.05) in HI compared with MOD. Total reproductive tract, uterus, and ovarian tissue expressed relative to BW were greater (P < 0.05) for HI compared with MOD. In conclusion, enhanced nutrition in early calfhood advances the ontogeny development of the HPO axis.

Transforming growth factor-β superfamily and interferon-τ in ovarian function and embryo development in female cattle: review of biology and application

Survival of the embryo and establishment of a pregnancy is a critical period in the reproductive function of female cattle. This review examines how the transforming growth factor-β (TGFB) superfamily (i.e. bone morphogenetic protein (BMP) 15, growth differentiation factor (GDF) 9, anti-Müllerian hormone (AMH)) and interferon-τ (IFNT) affect ovarian function and embryo development. The oocyte in a primary follicle secretes BMP15 and GDF9, which, together, organise the surrounding granulosa and theca cells into the oocyte-cumulus-follicle complex. At the same time, the granulosa secretes AMH, which affects the oocyte. This autocrine-paracrine dialogue between the oocyte and somatic cells continues throughout follicle development and is fundamental in establishing the fertilisation potential and embryo developmental competency of oocytes. The early bovine embryo secretes IFNT, which acts at the uterine endometrium, corpus luteum and blood leucocytes. IFNT is involved in the maternal recognition of pregnancy and immunomodulation to prevent rejection of the embryo, and supports progesterone secretion. Manipulation of BMP15, GDF9, AMH and IFNT in both invivo and invitro studies has confirmed their importance in reproductive function in female cattle. This review makes the case that a deeper understanding of the biology of BMP15, GDF9, AMH and IFNT will lead to new strategies to increase embryo survival and improve fertility in cattle. The enhancement of oocyte quality, early embryo development and implantation is considered necessary for the next step change in the efficiency of natural and assisted reproduction in cattle.

Plasma anti-Müllerian hormone concentration as a predictive endocrine marker for selection of donor lambs to improve success in juvenile in vitro embryo transfer programs

The use of juvenile invitro embryo transfer (JIVET) is limited by variation between prepubertal lambs in ovarian response to exogenous gonadotrophins. In cattle, anti-Müllerian hormone (AMH) is a predictive endocrine marker of antral follicle count. In this study we measured plasma AMH concentrations in lambs at 3 and 5 weeks of age and determined associations between AMH concentrations and ovarian response to gonadotrophins and invitro blastocyst production at 6-8 weeks of age in a JIVET program. At 5 weeks, AMH (n=38) was positively correlated with surface antral follicle count (r=0.87, P<0.001), blastocysts produced (r=0.92, P<0.001) and blastocysts produced as a proportion of oocytes collected (r=0.44, P<0.01) or cleaved (r=0.43, P<0.01). Similar associations were observed between AMH at 3 weeks (n=30) and follicle number (r=0.70, P<0.05) and blastocysts produced (r=0.87, P<0.05). Lambs with high (>2.2ngmL-1) compared with medium (0.4-2.2ngmL-1) and low (<0.4ngmL-1) AMH at 5 weeks had more antral follicles (mean (±s.e.m.) 118.7±13.9 vs 68.2±8.1 and 30.4±12.3 respectively; P<0.05) and more blastocysts produced (mean (±s.e.m.) 54.9±6.9 vs 18.9±4.0 and 7.5±6.1 respectively; P<0.05). These results suggest that AMH concentration at 5 weeks of age can be used to select donor lambs which enhance the success of JIVET programs.

Effect of dose and duration of FSH treatment on ovarian response in prepubertal calves

The objective of the study was to determine relative effects of dose (200 or 350 mg) and duration (4 or 7 days) of superstimulatory treatment on the ovarian response in prepubertal calves. Calves with similar antral follicular counts at wave emergence (n = 24) were given eight doses of either 25 or 44 mg pFSH every 12 h for 4 days or 14 doses of either 14 or 25 mg pFSH for 7 days beginning at the time of follicular wave emergence and 12.5 mg of pLH im 12 h after the last FSH treatment. On Day 4 of pFSH treatment, calves given 14 mg had fewer follicles ≥3 mm than those given 25 mg (15.1 ± 1.9 and 27.9 ± 3.3, respectively; P = 0.04). At the end of treatment (24 h post-LH), number of follicles ≥9 mm was greater in calves of groups treated with 350 than 200 mg (13.5 ± 1.8 and 8.8 ± 1.3, respectively; P = 0.02) and calves of groups treated for 7 than 4 days (13.3 ± 1.8 and 9.0 ± 1.3, respectively; P = 0.03). The number of spontaneous ovulations was greater in calves of groups treated for 7 than 4 days as was the total number of ovulations (9.7 ± 0.9 and 6.9 ± 1.0, respectively; P ≤ 0.05). In summary, a dose of 25 mg of pFSH per treatment given twice daily for 7 days resulted in a greater ovarian response than other superstimulatory treatments in prepubertal calves.

In vitro performance of Zebu (Bos indicus) and Taurus (Bos taurus) donor cow embryos

ABSTRACT In this study, the in vitro production of bovine embryos from zebu and taurine donors was compared. Cumulus-oocyte complexes (COCs) were obtained from 167 Bos taurus and 161 Bos indicus donors by ovum pick-up. COCs were classified based on their morphological quality, matured in incubators for 22 to 24 h in maturation medium, and then fertilized for 18 to 22 h. The zygotes were transferred to the culture medium for seven days. The embryos were classified as morula (OM), initial blastocyst (BI), blastocyst (BL), and expanded blastocyst (BX), before being transferred to synchronized recipient cows. Pregnancy was diagnosed 30-45 days post-transfer. The Bos indicus donors had a higher oocyte yield (n = 2556) than Bos taurus donors (n = 1903) (P = 0.008). The COCs from zebu donors had a better morphological quality than those from taurine donors (n = 689 vs. 444 for grade 1 COC, P < 0.0001; n = 681 vs. 509 for grade 2 COC, P = 0.010, for zebu and taurine donors, respectively). There were differences in embryo production percentages obtained from OM (0.44% from zebu and 6.42% from taurine, P = 0.017), BL (14.18% from zebu and 3.74% from taurine, P < 0.0001), and BX (81.43% from zebu and 75.13% from taurine, P < 0.0001). No significant difference was observed for embryo production from BI and pregnancy rate (P > 0.05). The Bos indicus cows showed greater oocyte recovery, number of viable oocytes, and production of viable embryos than the Bos taurus cows.

Intensive use of IVF by large-scale dairy programs

The number of embryos produced by in vitro fertilization (IVF) has grown exponentially in recent years. Recently, for the first time, the number of embryos produced and transferred in vitro was significantly higher than the number developed in vivo worldwide. In this context, a particular boost occurred with ovum pick-up (OPU) and in vitro embryos produced in North America, and this technology is becoming more prominent for commercial dairy farms. However, despite many advances in recent decades, laboratories and companies are looking for methods and alternatives that can be used in collaboration with the existing process to improve it. Among the strategies used to improve the dairy industry are the use of genomic analysis for the selection of animals with desired traits or as an evaluation tool of oocyte and embryo quality, the optimization of the collection and use of gametes from prepubertal females and males, the effective use of sexed semen, and improvements in culture media and methods of embryo cryopreservation. Thus, this review aims to discuss the highlights of the commercial use of IVF and some strategies to increase the application of this technique in large-scale dairy programs.

Challenges to increase the AI and ET markets in Brazil

Artificial insemination (AI) and embryo transfer (ET) are the most widely used biotechnologies in the world with the goal of increasing genetic gain and improving reproductive efficiency of beef and dairy herds. The protocols for ovulation synchronization for timed AI (TAI) or ET (TET) are tools that allow artificial insemination or transfer of a high number of embryos in a pre-established moment and without the necessity of estrous detection. Currently, 86% of inseminations in Brazil are performed using TAI (13.6 million TAI out of a total of 15.4 million doses of semen marketed in 2018). With the use of TAI, it was possible to verify that the percentage of artificially inseminated females in Brazil went from 5.8% in 2002 to 13.1% in 2018. The ET market also presented considerable growth in the last 20 years. There was an increase of approximately 8 fold in the number of produced embryos, escalating from 50,000 in 1999 to 375,000 in 2017. In this period, there was a significant increase on the in vitro embryo production, which represented 92.1% of embryos produced in Brazil in 2017. Also, in this period, there was an increase on the embryo production of dairy breeds and reduction on the embryo production of zebu breeds in comparison to data from the early 2000's. TET increases significantly the number of recipients suitable to receive an embryo. After synchronization, 75 to 85% of recipients present a suitable CL for ET without estrous detection. Currently, many synchronization and resynchronization protocols for TAI/TET have been studied to attend different managements, breeds and animal categories, with predictable and satisfactory results. With the intensification of the use of these biotechnologies, it is possible to obtain elevated reproductive efficiency with increase on the genetic gain, which determines greater productivity and economic return for dairy and beef farms. However, the challenge to keep the market growing in the next decade could depend on some factors, such as: increase of the extension services for producers and of the extension training for specialists, improvement of the technological advances to develop more efficient and cost-effective products and practical protocols, increase the integration between universities, research institutes, veterinarians and industries and also, asses market demand for production of animal protein with higher quality, efficiency and environmental and economic sustainability.

Evaluation of anti-mullerian hormone in heifers and anestrus Murrah buffaloes

An experiment was conducted to quantify the anti-mullerian hormone (AMH) concentration in heifers and anestrus Murrah buffaloes during fortnight blood collections for 3 months. Two groups of heifer and anestrus Murrah buffaloes were formed on the basis of record and actual per rectal examination. Serum AMH concentration was determined by ELISA method, using bovine AMH ELISA kit. Nonsignificant difference was recorded in AMH concentration (pg/ml) in heifer and anestrus buffaloes during fortnight collection (0, 15, 30, 45, 60 and 75). Highly significant individual variation was observed in heifer and anestrus buffaloes in this study. Heifers (6) with AMH concentration above 200 pg/ml were pregnant and 4 heifers with AMH concentration below 200 pg/ml were non pregnant. AMH concentration is a reliable phenotypic marker to predict the number of healthy follicles and oocytes, in ovaries and predict the future potential of heifers and young adult buffaloes. The cut-off value of AMH concentration in Murrah heifers buffaloes as a marker of fertility may be 200 pg/ml. However, study with more number of buffaloes is required to determine the accurate cut-off value of AMH concentration.

Superstimulation prior to the ovum pick-up improves the in vitro embryo production in nulliparous, primiparous and multiparous buffalo (Bubalus bubalis) donors

The aim of this study was to evaluate the ovarian follicular population, the oocyte yield and the in vitro embryo production (IVEP) of nulliparous (NU), primiparous (PR) and multiparous (MU) buffalo donors submitted to the superstimulation with FSH prior to the ovum pick-up (OPU). A total of 54 buffalo donors (18 NU, 15 PR and 21MU) received an intravaginal progesterone device (1.0 g) plus estradiol benzoate [2.0 mg, intramuscular (im)] at random stage of the estrous cycle (Day 0) during the breeding season (autumn and winter). Buffaloes from different categories were then randomly allocated to one of two groups (Control or FSH), in a cross-over experimental design. Buffalo donors in the Control group received no further treatment, whereas buffalo donors in the FSH group received a total dosage of 200 mg im of FSH on Days 4 and 5, in four decreasing doses 12 h apart (57, 57, 43 and 43 mg). On Day 7, the progesterone device was removed and the OPU procedure was performed in both groups. The same semen was used across all replicates and donor category. Data were analyzed by the GLIMMIX procedure of SAS 9.4^®. There was no interaction between FSH treatment and animal category for all analyzed variables. Furthermore, no differences between animal category (P = 0.73) and FSH treatment (P = 0.53) were observed regarding the total follicles aspirated. However, the FSH treatment increased (P < 0.001) the proportion of large (>10 mm; FSH = 16.2% and Control = 2.0%) and medium-sized follicles (6-10 mm; FSH = 36.3% and Control = 6.1%) available for the OPU procedure. The total of recovered oocytes was greater in NU than in MU, and PR were similar to NU and MU (P = 0.05). No effect of FSH treatment was observed (P = 0.85) for this variable. Buffalo donors treated with FSH had a greater viable oocytes rate (P = 0.03), blastocyst rate (P = 0.03) and embryo yield per OPU-IVEP session (P = 0.07), however, no category effects were observed for these variables. These results provided evidence that superstimulation with FSH increased the proportion of large and medium-sized follicles available for the OPU procedure. Consequently, the FSH treatment enhanced the proportion of viable oocytes for culture and resulted in greater blastocyst rates and embryo yield per OPU-IVEP session in all buffalo donors categories.

Antral follicle population in prepubertal and pubertal heifers

The antral follicle count (AFC) is an important tool in the selection of bovine females destined for biotechnology. However, little is known about AFC in prepubertal and pubertal heifers. Some challenges inherent to the physiology of young females must be considered to achieve efficient rates with different procedures, such as ovum pick-up and IVF. This paper covers some important topics about ovarian physiology related to the population of antral follicles and reproductive efficiency in young female cattle.

Presence of anti-Müllerian hormone (AMH) during follicular development in the porcine ovary

BACKGROUND

Anti-Müllerian hormone (AMH) is expressed by granulosa cells of developing follicles and plays an inhibiting role in the cyclic process of follicular recruitment by determining follicle-stimulating hormone threshold levels. Knowledge of AMH expression in the porcine ovary is important to understand the reproductive efficiency in female pigs.

RESEARCH AIM

In the present study we investigated the expression of AMH during follicular development in prepubertal and adult female pigs by immunohistochemistry, laser capture micro-dissection and RT-qPCR.

RESULTS AND CONCLUSION

Although in many aspects the immunohistochemical localization of AMH in the porcine ovary does not differ from other species, there are also some striking differences. As in most species, AMH appears for the first time during porcine follicular development in the fusiform granulosa cells of recruited primordial follicles and continues to be present in granulosa cells up to the antral stage. By the time follicles reach the pre-ovulatory stage, AMH staining intensity increases significantly, and both protein and gene expression is not restricted to granulosa cells; theca cells now also express AMH. AMH continues to be expressed after ovulation in the luteal cells of the corpus luteum, a phenomenon unique to the porcine ovary. The physiological function of AMH in the corpus luteum is at present not clear. One can speculate that it may contribute to the regulation of the cyclic recruitment of small antral follicles. By avoiding premature exhaustion of the ovarian follicular reserve, AMH may contribute to optimization of reproductive performance in female pigs.

Hormonal stimulation in 4 to 7 months old Nelore (Bos taurus indicus) females improved ovarian follicular responses but not the in vitro embryo production

The inclusion of pre-pubertal bovine females in reproductive management could allow in vitro embryo production and reduce generation interval, thereby causing faster genetic gain of the herd. However, oocytes of pre-pubertal females have lower competence, blastocyst production, and pregnancy rates than those collected from pubertal animals. This study aimed to evaluate the effect of an induced hormonal stimulation on the serum concentrations of Anti-Mullerian hormone (AMH) and FSH, ovarian responses, ovum pick up (OPU), and in vitro produced embryos (IVP) from oocytes obtained from four-to seven-months old Nelore female cattle. In a crossover design, these females were randomly allocated into: 1) Treated Group (TG, n = 9): the animals were subjected to a hormonal protocol (implanted progesterone device, estradiol benzoate, LH, and FSH) from Day 0 (the start of the treatment) to Day 7 (OPU day), and 2) Control Group (CG, n = 9): the females did not receive any hormonal stimulation, but they had ablation of their largest follicles on Day 2 of experiment. Blood collection for serum FSH measurements was done on Days 5, 6, 7, and 8, and collection for serum AMH measurements was done on Days 5 and 8. As hypothesized, TG had higher serum FSH concentrations (p < 0.05) on Day 5 (1.16 ± 0.31 ng/mL), Day 6 (1.21 ± 0.45 ng/mL), and Day 7 (0.95 ± 0.26 ng/mL) than CG (0.56 ± 0.17 ng/mL on Day 5, 0.60 ± 0.25 ng/mL on Day 6, and 0.60 ± 0.14 ng/mL on Day 7). However, serum AMH concentrations were neither significantly different (p > 0.05) between CG and TG, nor between the collection days. Hormonal stimulation also increased (p < 0.05) total follicular population (20.0 ± 4.95 CG vs 26.66 ± 4.24 TG), ovarian diameter (13.08 ± 1.0 mm CG vs 14.81 ± 1.38 mm TG) and number of follicles ≥2.5 mm (6.88 ± 2.14 CG vs 11.55 ± 4.09 TG). In TG, grades I and II oocytes predominated, whereas, in CG grades III and IV oocytes were more abundant (p < 0.05). No significant increases (p > 0.05) in the cleavage (49.33% CG vs 51.42% TG), cleavage > 4 cells (9.33% CG vs 16.19% TG), and blastocysts rates (1.33% CG vs 8.57% TG) were seen in TG. This hormonal protocol increased serum FSH concentrations that possibly contributed to increases in the observed follicle, as well as improving oocyte quality. This exogenous hormonal stimulation increased available oocytes numbers for IVP, despite no increase in the in vitro embryo production efficiency.

Anti-Müllerian hormone as a marker of embryo production in ruminants

This review describes the role of anti-Müllerian hormone (AMH) in embryo production for assisted reproductive technologies in ruminants. AMH is a marker of healthy follicles and oocytes, a reliable marker of gonadotropin-responsive follicles, and an indicator of longevity and productivity in dairy animals. The best times to measure AMH levels in order to select cows for embryo production is during oestrus and the period after the 12th day of the oestrous cycle. This allows animals with AMH concentrations below 87 pg/mL at oestrus or less than 74 pg/mL for multiple ovulation embryo transfer to be eliminated. Good oocyte donors, which have higher antral follicle counts, can be identified based on their higher AMH levels. In sheep and goats, the blood AMH level can serve as a marker of the animal’s potential to produce high or low numbers of high-quality embryos. A plasma AMH level of 97 pg/mL in sheep has been shown to be the optimum cut-off point to predict fertility and can be useful in selecting replacement ewes.

The relationship between circulating concentration of AMH and LH content in the follicle stimulating hormone (FSH) preparations on follicular growth and ovulatory response to superovulation in water buffaloes

The relationship between circulating concentration of anti-mullerian hormone (AMH) and the LH content of follicle stimulating hormone (FSH) preparation on follicular growth and ovulatory response in water buffaloes was evaluated. A single blood sample was taken from cows (N=31; age: 9.06±0.98years) to determine systemic AMH. Animals with concentrations higher or lower than 194±30pg/ml were placed into LOW and HIGH AMH groups and were assigned randomly to be superovulated FSH containing either a high (FSHp, HLH) or low (FolltropinV, LLH) LH content. Follicular growth and ovulation were monitored using transrectal ultrasonography. In animals with HIGH systemic AMH, treatment with FSH with a high LH content was associated with more small follicles (AMH X FSH; P=0.02). AMH had no effect on small follicles in animals treated with LLH. Females with a HIGH AMH had greater numbers of small follicles (P=0.01) and total follicles (P=0.005) than LOW AMH cows. Animals treated with HLH had more small follicles (P=0.001) but fewer large (P<0.001) and total follicles (P=0.0005) than those treated with LLH. Among animals with HIGH AMH, those treated with LLH, ovulated more follicles than those treated with HLH. (AMH X FSH; P=0.03). In conclusion, selecting animals with high AMH concentration and the use of FSH preparations with a lower LH content may improve the superovulatory response in water buffaloes.

Ovulation rate, antral follicle count, and circulating anti-Müllerian hormone in Trio allele carriers, a novel high fecundity bovine genotype

High fecundity genotypes in sheep are a valuable model to study the physiological mechanisms underlying follicle selection and the control of ovulation rate. Similar genotypes in cattle had not been described until the recent identification of a major bovine allele, termed Trio, which had a large effect on ovulation rate. The present study was designed to evaluate ovulation rate, antral follicle count (AFC), circulating ant-müllerian hormone (AMH), and the association among these measures in unstimulated and superstimulated Trio carrier cattle. We hypothesized that AFC and AMH would be variable among individual cows but would be similar between Trio carriers and non-carrier control cows and that there would be no association between these measures of follicle numbers and ovulation rate. In experiment 1, ovulation rate was determined during 4 consecutive estrous cycles in Trio carriers (n = 34) and non-carrier controls (n = 27). Ovulation rate, on average, was greater (P < 0.01) in Trio carriers (3.5 ± 0.2) compared to non-carrier controls (1.1 ± 0.1) with ∼70% of carrier cycles (n = 136) having 3-4 ovulations while only ∼5% had single ovulations. In contrast, non-carrier cycles (n = 108) were mostly single ovulation (89%) with none having more than two ovulations. In experiment 2, AFC, determined at wave emergence, was not different (P = 0.54) between Trio carriers (24.5 ± 1.3; n = 45) and non-carrier controls (23.1 ± 0.9; n = 37), and no correlation was found between AFC and mean ovulation rate in either genotype (r = -0.009 and r = -0.07; P > 0.70, respectively). In Experiment 3, circulating AMH was also not different between genotypes (P = 0.65) while correlations were found between AFC and AMH in Trio carriers (r = 0.43; P = 0.05; n = 27) and non-carrier controls (r = 0.78; P < 0.01; n = 19). In experiment 4, AFC and AMH were determined in Trio-carriers (n = 9) in relation to a synchronized follicular wave which was unstimulated or stimulated with exogenous FSH. Stimulation with FSH increased ovulation rate, compared to unstimulated Trio carriers, however no association was found between AFC or AMH and ovulation rate regardless of whether superstimulation with exogenous FSH was used. In conclusion, the novel high fecundity bovine genotype Trio, results in consistent multiple ovulations despite having similar AFC and AMH. Therefore, our results suggest that differences in antral follicle numbers during the final stages of follicle development are not a key component of the mechanism underlying multiple ovulations in Trio carriers.

Anti-Müllerian Hormone (AMH) and fertility management in agricultural species

A reliable, easy to assess marker for fertility in agricultural species would be highly desirable and Anti-Müllerian Hormone (AMH) is a promising candidate. This review summarizes recent findings concerning AMH and its role in fertility management, mainly in cattle. It focuses on (1) alterations in circulating AMH concentrations from birth to puberty and during estrous cycles; (2) correlation of circulating AMH concentrations with ovarian follicle numbers and ovarian reserve; (3) factors that impact circulating AMH concentrations; (4) use of AMH as a predictor of fertility. Circulating AMH concentrations can be easily and reliably measured with a single blood sample in adult cattle because AMH varies minimally during the estrous cycle and is repeatable across multiple cycles. Circulating AMH concentrations are positively associated with several measures of fertility. Dairy heifers with low compared with higher AMH concentrations subsequently had lower pregnancy rates, higher probability of being culled after birth of their first calf and shorter herd longevity. Also, AMH is predictive of response to superovulation in cattle and sheep. Several factors contribute to the variability in AMH concentrations among individuals; for example, beef cattle have higher AMH than dairy cattle. Nutritional imbalances, disease and endocrine disruptors during fetal life may negatively program the size of the ovarian reserve and consequently serum AMH concentrations and potential fertility in adulthood. We conclude that AMH may be a predictor of fertility and herd longevity in cattle, whereas in sheep and other farm species, the potential association between AMH and reproductive performance remains largely unexplored.Free Italian abstract: An Italian translation of this abstract is freely available at http://www.reproduction-online.org/content/154/1/R1/suppl/DC1.