How great thou ART: biomechanical properties of oocytes and embryos as indicators of quality in assisted reproductive technologies

Assisted Reproductive Technologies (ART) have revolutionized infertility treatment and animal breeding, but their success largely depends on selecting high-quality oocytes for fertilization and embryos for transfer. During preimplantation development, embryos undergo complex morphogenetic processes, such as compaction and cavitation, driven by cellular forces dependent on cytoskeletal dynamics and cell-cell interactions. These processes are pivotal in dictating an embryo's capacity to implant and progress to full-term development. Hence, a comprehensive grasp of the biomechanical attributes characterizing healthy oocytes and embryos is essential for selecting those with higher developmental potential. Various noninvasive techniques have emerged as valuable tools for assessing biomechanical properties without disturbing the oocyte or embryo physiological state, including morphokinetics, analysis of cytoplasmic movement velocity, or quantification of cortical tension and elasticity using microaspiration. By shedding light on the cytoskeletal processes involved in chromosome segregation, cytokinesis, cellular trafficking, and cell adhesion, underlying oogenesis, and embryonic development, this review explores the significance of embryo biomechanics in ART and its potential implications for improving clinical IVF outcomes, offering valuable insights and research directions to enhance oocyte and embryo selection procedures.

Nutritional Strategies to Promote Bovine Oocyte Quality for In Vitro Embryo Production: Do They Really Work?

The ability of bovine oocytes to reach the blastocyst stage (i.e., embryo with around 150 cells in cattle) in vitro can be affected by technical (e.g., culture medium used) and physiological factors in oocyte donors (e.g., age, breed). As such, the nutritional status of oocyte donors plays a significant role in the efficiency of in vitro embryo production (IVEP), and several nutritional strategies have been investigated in cattle subjected to ovum pick-up (OPU). However, there is no clear consensus on the reliability of nutritional schemes to improve IVEP in cattle. Available evidence suggests that a moderate body condition score (i.e., 3 in a 1-5 scale) in cattle is compatible with a metabolic microenvironment in ovarian follicles that will promote embryo formation in vitro. The usefulness of fatty acid and micronutrient supplementation to improve IVEP in cattle is debatable with the current information available. Overall, the supply of maintenance nutritional requirements according to developmental and productive stage seems to be enough to provide bovine oocyte donors with a good chance of producing embryos in vitro. Future nutrition research in cattle using OPU-IVEP models needs to consider animal well-being aspects (i.e., stress caused by handling and sampling), which could affect the results.

Improving Cryopreservation Efficiency and Pregnancy Rate through Superovulation with Follicle-Stimulating Hormone in Korean Hanwoo Cows via Ovum Pick Up

The aim of this study was to devise an efficient technique for generating embryos from high-quality bovine females. Oocytes were collected from 20 control and 15 Hanwoo (Bos taurus coreanae) females treated with the FSH. A combination of decreasing FSH doses (36, 36, 24, and 24 mg, 12 h apart), progesterone, estrogen, and prostaglandins were administered to synchronize and mildly stimulate the animals. The FSH-treated group (1125 oocytes) and control group (1022 oocytes) exhibited a higher proportion of grade A and B oocytes (88.2%) than the other grades (p < 0.05), with most at the germinal vesicle 2 stage (64.0%). Moreover, the FSH-treated group achieved a notably higher blastocyst rate (44.7%) compared to the control group (31.1%) (p < 0.05). After undergoing vitrification and in vitro culture (IVC) warming, embryos in the FSH group exhibited higher re-expansion rates (grade 1: 86.9%; grades 2 and 3: 57.9%) compared to those in the control (p < 0.05). This highlights the positive impact of FSH treatment on in vitro embryo production (IVEP) and the OPU rate.

Blastulation time measured with time-lapse system can predict in vitro viability of bovine blastocysts

The objective of this study was to evaluate the time of blastulation monitored by time-lapse technology to predict in vitro viability of bovine blastocysts. This technology can be a powerful tool for bovine embryos selection with higher implantation capacity and competence. Also, in humans an early blastulation is associated with higher quality and pregnancy rate. Cumulus oocyte complexes (COCs) were matured for 20 to 22 h and then fertilized by co-incubation of COCs and spermatozoa (10,000 sperm per oocyte) for 18 h. Presumptive zygotes were placed individually in microwells, in droplets of commercial culture medium. The Primo Vision TL system (EVO+; Vitrolife) captured digital images of developing embryos every 15 minutes. The time frame from IVF to the start of blastulation (tSB) and to blastocyst development (tB) was recorded. After day 7.5, the blastocysts were in vitro culture for 48 h until day 9.5 after IVF to evaluate post hatching development. In vitro viability was evaluated at day 9.5: those with a diameter greater than 200 μm and a total cell count greater than 180 were classified as viable (value 1), while the rest were classified as non in vitro viable (value 0). The area under the ROC curve (AUC) was estimated to determine the predictive power of in vitro viability through blastulation time. In addition, binary logistic regression analysis was used to generate a mathematical model with morphokinetic variables that allow the best prediction of in vitro viability. In 13 sessions, the blastocyst production rate was 46.2% (96/208). The cut-off time to discriminate early or late blastulation was 149.8 h. The post-hatching development of the embryos with early blastulation was 63.3% (31/49), being statistically superior (p = 0.001) than the late blastulation group 14.9% (7/47). Likewise, the time of blastulation showed an accuracy of 90.8% (p < 0.001) in predicting in vitro viability of bovine blastocysts. In conclusion, the selection of blastocysts based on blastulation time (< 155 h) and blastocyst diameter measured on day 7.5 after IVF (> 180 μm) maximizes the in vitro viability.

Lipid peroxidation in bull semen influences sperm traits and oxidative potential of Percoll®-selected sperm

Although bovine embryo in vitro production (IVP) is a common assisted reproductive technology, critical points warrant further study, including sperm traits and oxidative status of sperm for in vitro fertilization (IVF). Our aim was to evaluate whether the lipid peroxidation index of commercial bull semen is influenced by sperm traits and oxidative status of sperm populations selected using Percoll® gradient. Semen straws from 48 batches from 14 Nelore bulls were thawed individually, analyzed for motility and subjected to Percoll selection. After Percoll, the lipid peroxidation index of the extender was evaluated, whereas selected sperm were analyzed for motility, acrosome and membrane integrity, mitochondrial membrane potential, chromatin resistance and oxidative potential under IVF conditions. Batches were divided retrospectively in four groups according to lipid peroxidation index. Sperm from Group 4 with the lowest index of lipid peroxidation had, after Percoll selection, greater plasma membrane integrity (81.3%; P = 0.004), higher mitochondrial potential (81.1%; P = 0.009) and lower oxidative potential (135.3 ng thiobarbituric acid reactive substances (TBARS)/ml; P = 0.026) compared with Group 1 with highest lipid peroxidation index (74.3%, 73% and 213.1 ng TBARS/ml, respectively). Furthermore, we observed negative correlations for the lipid peroxidation index with motility, membrane integrity and mitochondrial potential, and positive correlations with oxidative potential. In conclusion, oxidative stress in semen straws, as determined using lipid peroxidation in the extender, is associated with sperm traits and their oxidative potential under IVF conditions. These results provided further insights regarding the importance of preventing oxidative stress during semen handling and cryopreservation, as this could affect sperm selected for IVF. Finally, Percoll selection did not completely remove sperm with oxidative markers.

Developmental kinetics and viability of bovine embryos produced in vitro with sex-sorted semen

The present study aimed to elucidate the developmental kinetics, growth potential, and viability of bovine embryos produced in vitro with sexed semen. Bovine oocytes were fertilized in vitro using unsorted and X-sorted semen from the same Holstein bulls, and the kinetics of in vitro development were continuously monitored for 10 d through time-lapse cinematography. The blastocyst formation rate was lower in the X-sorted group than in the unsorted group (P < 0.01), whereas the normal fertilization rate did not differ between groups. Morphokinetic evaluation revealed that the incidence of blastomere fusion during the first cleavage division, termed reverse cleavage, was higher in the X-sorted group (P < 0.01). Furthermore, embryos produced with X-sorted semen showed slower growth throughout the developmental period than embryos produced with unsorted semen (P < 0.01). The cell number of the trophectoderm and inner cell mass of blastocysts was reduced in the X-sorted group (P < 0.01). In embryos that developed to the blastocyst stage, the hatchability (P < 0.05), chromosomal normality (P < 0.01), and survivability after the conventional frozen-thawing process (P < 0.05) were reduced in the X-sorted group compared to that in the unsorted group, indicating a compromised viability of embryos derived from X-sorted semen. Taken together, the first cleavage dysmorphism, delayed embryo growth, and impaired viability of embryos developed to the blastocyst stage may explain the mechanism of reduced fertility in embryos derived from sexed semen. The kinetic evaluation of early embryo development and de-selection of embryos presenting the aberrant first cleavage would be valid for clinical application to produce sexed embryos with high implantation potential.

One-step automated bioprinting-based method for cumulus-oocyte complex microencapsulation for 3D in vitro maturation

Three-dimensional in vitro maturation (3D IVM) is a promising approach to improve IVM efficiency as it could prevent cumulus-oocyte complex (COC) flattening and preserve its structural and functional integrity. Methods reported to date have low reproducibility and validation studies are limited. In this study, a bioprinting based production process for generating microbeads containing a COC (COC-microbeads) was optimized and its validity tested in a large animal model (sheep). Alginate microbeads were produced and characterized for size, shape and stability under culture conditions. COC encapsulation had high efficiency and reproducibility and cumulus integrity was preserved. COC-microbeads underwent IVM, with COCs cultured in standard 2D IVM as controls. After IVM, oocytes were analyzed for nuclear chromatin configuration, bioenergetic/oxidative status and transcriptional activity of genes biomarker of mitochondrial activity (TFAM, ATP6, ATP8) and oocyte developmental competence (KHDC3, NLRP5, OOEP and TLE6). The 3D system supported oocyte nuclear maturation more efficiently than the 2D control (P<0.05). Ooplasmic mitochondrial activity and reactive oxygen species (ROS) generation ability were increased (P<0.05). Up-regulation of TFAM, ATP6 and ATP8 and down-regulation of KHDC3, NLRP5 expression were observed in 3D IVM. In conclusion, the new bioprinting method for producing COC-microbeads has high reproducibility and efficiency. Moreover, 3D IVM improves oocyte nuclear maturation and relevant parameters of oocyte cytoplasmic maturation and could be used for clinical and toxicological applications.

Meta-analysis to determine effects of treatment with FSH when there is progestin-priming on in-vitro embryo production using ovum pick-up in Bos taurus cows

Treatments with follicle stimulating hormone (FSH) to enhance ovarian follicular development before ovum pick-up (OPU) are important for improving in-vitro embryo production (IVEP) procedures in cows, however, their procedural efficacy needs to be evaluated. The objective of the present study was to use meta-analytic methods to determine the effects of FSH treatments prior to OPU when there is progestin-priming on ovarian functions and IVEP in parous Bos taurus cows (n = 243). The literature was systematically reviewed and data from eight experiments, with 23 treatment means including 448 OPU sessions, were used for analyses. All eight experiments included a group of cows in which there was no FSH treatment (CON), and treatment with FSH before OPU to conduct IVEP. Mixed models were fitted using MIXED and GLIMMIX procedures of SAS. Additionally, classical meta-analytical statistics were also fitted using METAN and METAREG procedures of STATA. Models included fixed effects of treatment (i.e., CON and FSH) and random effect of the experiment, and data were weighted using the inverse of the SEM squared to account for precision of each experiment. Number of medium sized follicles, quality of oocytes, and transferable embryos were greater (P < 0.05) in FSH-treated as compared with cows of the CON group, without indications of publication bias or heterogeneity of data. Taken together, the results from the present study lead to the recommendation for treatments with FSH prior to OPU for IVEP when there was progestin-priming imposed to obtain a large number of transferable embryos for economic sustainability of commercial embryo transfer programs in parous non-lactating Bos taurus cows.

Optimization of a 5-day fixed-time embryo transfer (FTET) protocol in heifers I. Manipulation of circulating progesterone through reutilization of intravaginal progesterone devices during FTET

The objectives of the present study were to: 1) compare the reproductive efficiency of embryo transfer (ET) recipients after synchronization of estrus or a 5-day synchronization of ovulation protocol for fixed time ET (FTET), and 2) determine the effect of reutilization of intravaginal P4 devices (CIDRs), up to four times, in a 5-day FTET protocol. In Experiment 1, 817 dairy heifers were assigned to one of three groups: PGF + estrus detection, 5-d FTET protocol with new (1.38 g P4) or 2nd use CIDR (previously used once for 5 d). Fresh in vitro produced embryos were transferred 7 ± 1 day after estrus (PGF + estrus) or GnRH (5-day FTET). Utilization rate (transferred/treated) was greater (P < 0.001) in heifers submitted to FTET compared to ET after estrus, however pregnancies per ET (P/ET) were not different (P > 0.10). As a result, pregnancy per treated (P/treated) recipient was greater (P < 0.05) in heifers in the 5-day FTET protocol. In Experiment 2, 40 dairy heifers without a corpus luteum (CL) were randomly allocated into one of four groups using new, 2nd use, 3rd use (previously used twice for 5 d/each), or 4th use (previously used thrice for 5 d/each) CIDRs. Circulating P4 was reduced (P < 0.01) with each reutilization. In Experiment 3, ovarian follicular dynamics were evaluated in 238 dairy heifers submitted to a 5-day protocol with either new, 2nd use, 3rd use or 4th use CIDRs at random stages of the estrous cycle. Prostaglandin F2α (PGF) was administered at CIDR removal and again 24 h later. Ovulation was induced by GnRH treatment 72 h after CIDR removal. Preovulatory follicle diameter increased (P < 0.001) progressively with increasing CIDR reutilization. Ovulation rate did not differ between treatments, however, interval from CIDR removal to ovulation decreased (P < 0.001) in heifers receiving 3rd and 4th use CIDRs compared to new or 2nd use. Finally, in Experiments 4 and 5, 1203 heifers submitted to a 5-day FTET protocol were randomly assigned to receive either a new CIDR, a 3rd use CIDR (Experiment 4) or a 4th use CIDR (Experiment 5). Despite the increase in CL volume on D5 in heifers treated with 3rd use (P = 0.03) or 4th use CIDRs (P < 0.01), there were no differences (P > 0.05) in utilization rate, P/ET, or P/treated. Thus, use of a 5-day FTET synchronization protocol improves reproductive efficiency by increasing recipient utilization, and reutilization of CIDRs up to four times in recipient dairy heifers does not compromise reproductive performance.

In vitro breeding: application of embryonic stem cells to animal production†

Embryonic stem cells (ESCs) are derived from the inner cell mass of preimplantation blastocysts. For decades, attempts to efficiently derive ESCs in animal livestock species have been unsuccessful, but this goal has recently been achieved in cattle. Together with the recent reconstitution of the germ cell differentiation processes from ESCs in mice, these achievements open new avenues for the development of promising technologies oriented toward improving health, animal production, and the environment. In this article, we present a strategy that will notably accelerate genetic improvement in livestock populations by reducing the generational interval, namely in vitro breeding (IVB). IVB combines genomic selection, a widely used strategy for genetically improving livestock, with ESC derivation and in vitro differentiation of germ cells from pluripotent stem cells. We also review the most recent findings in the fields on which IVB is based. Evidence suggests this strategy will be soon within reach.

Contribution of Reproduction Management and Technologies to Genetic Progress in Horse Breeding

Reproductive technologies aim at improving fertility with the ultimate result of improving genetic selection. In equidae, the respective contribution of different methods of horse management and breeding to genetic progress remain difficult to evaluate as breeding strategies affect the number of offspring per mare or stallion whereas different selection methods (based on pedigree, performance, genomics or progeny's performance) will be applicable at different ages, leading to different accuracy in the estimation of the breeding value. Here, a mathematical model was applied to evaluate theoretical genetic progress depending on breeding conditions in horses. The model showed that for breeding systems ranging from 0.6 to 2 foals/year/mare and from 10 to 150 foals/year for stallions, when selection of the best animals is strictly made by a truncation, the genetic progress is accelerated by (1) increasing the number of offspring per year, (2) the start of reproduction as soon as the age of 2 in both sexes, and (3) reducing the number of years of use for stallions from 10 to 5 years. The calculation showed that using all ways of improvement could provide an increase in genetic progress of up to +270% and +226% in mares and stallions, respectively, above the basal reference situation of 100%. In the Selle Français breed, the observed reproductive management parameters (10 years generation interval, 10 foals/stallion and 0.55 foals/mare) are close to the worst conditions of the model. In addition, the best mares are not selected for breeding. In conclusion, new reproductive technologies, genomic selection, and breeding younger animals will increase genetic gain.

Follicle priming by FSH and pre-maturation culture to improve oocyte quality in vivo and in vitro

Nowadays there is strong demand to produce embryos from premium quality cattle, and we can produce embryos using oocytes collected from living premium animals by ovum-pick up (OPU) followed by in vitro fertilization (IVF). However, the developmental competence of IVF oocytes to form blastocysts is variable. The developmental competence of oocytes depends on the size and stages of follicles, and follicle-stimulating hormone priming (FSH-priming) prior to OPU can promote follicular growth and improve the developmental competence of oocytes. Furthermore, following the induction of ovulation using an injection of luteinizing hormone or gonadotropin-releasing hormone after FSH-priming, we can collect in vivo matured oocytes from ovulatory follicles, which show higher developmental competence than oocytes matured in vitro. However, the conventional protocols for FSH-priming consist of multiple FSH injection for 3-4 days, which is stressful for the animal and labor-intensive for the veterinarian. In addition, these techniques cannot be applied to IVF of oocytes collected from bovine ovaries derived from slaughterhouses, which are important sources of oocytes. Here, we review previous research focused on FSH-priming, especially for collecting in vivo matured oocytes and a simplified method for superstimulation using a single injection of FSH. We also introduce the previous achievements using in vitro pre-maturation culture, which can improve the developmental competence of oocytes derived from non-stimulated animals.

In vitro growth of immature bovine follicles and oocytes

The limitation in the supply of mature, fertilisable oocytes constitutes a major impediment to increasing the success of assisted reproduction, stem cell derivation and cloning in domestic species. Techniques are being developed to grow immature oocytes invitro that have the potential to increase the supply of oocytes. Mouse oocytes can be cultured from initial stages of development to maturity, and live young have been produced, but for domestic species, such as cows, with long growth periods, invitro systems that allow complete growth of oocytes contained within primordial follicles to maturity is technically challenging and has not yet been achieved. For cows, several culture systems have been developed that support specific developmental stages, but a multistep culture system will be required for complete growth invitro. This review highlights the steps that will be required to achieve the goal of growing oocytes invitro.

Growth potential of bovine embryos presenting abnormal cleavage observed through time lapse cinematography

Time-lapse monitoring (TLM) has emerged as a novel technology for the continuous and noninvasive evaluation of embryos. TLM has revealed the prevalence of specific dysmorphisms such as abnormal development during the early-cleavage stage of embryos. However, little information is available on the prevalence and consequences of abnormal cleavage in bovine embryos. Hence, this study aimed to investigate growth potential of bovine embryos presenting abnormal cleavage, such as reverse cleavage (RC), direct cleavage (DC), and irregular and unsmooth ruffling of the oolema membrane (ruffling). Bovine embryos derived through in vitro fertilization (IVF) were cultured in the microwell culture dishes, and the kinetics of in vitro development were observed through TLM at 20-min intervals for 10 d. Approximately 36% of embryos that developed into a blastocyst presented abnormal cleavage. Morphokinetic evaluations revealed that RC, DC, and ruffling embryos showed slower development compared to embryos with normal cleavage (P < 0.01). Embryos with RC and DC, but not ruffling, revealed impaired hatchability (P < 0.05) with increased collapses of the blastocyst cavity until hatching (P < 0.0001). Moreover, the RC and DC embryos presented increased chromosomal aneuploidy (P < 0.05). These results suggest a compromised viability of embryos with RC and DC. This is the first report that clarified the effect of abnormal cleavage on the morphokinetics and growth potential of bovine IVF embryos. Results indicate that the kinetic evaluation of bovine embryos using the time-lapse imaging system will be beneficial for selecting embryos with a high viability.

Acquisition of developmental competence and in vitro growth culture of bovine oocytes

Recently, the demand of transferable embryos in cattle industry is increasing, and the number of embryos produced in vitro is also increasing in the world. Although oocytes are collected from individual elite cattle by ovum-pick up (OPU) and used for in vitro production (IVP) of embryos, the cattle are mono-ovulatory animal. It means that most of oocytes collected from ovaries are destined to degenerate. To improve the IVP efficiency, we should predict the developmental competence of oocytes correctly and culture them by the suitable way. In addition, in vitro production of bovine oocytes by in vitro growth (IVG) culture system will become a candidate of supply source of oocytes for IVP. If we can produce high competent oocytes by IVG, IVP efficiency will be improved and the genetic improvement of cattle will be dramatically accelerated. In the review, I introduce our researches related to oocyte morphology, the developmental competence, and the production of oocytes having high developmental competence by IVG culture.

Effects of supplemental progesterone using a CIDR insert on pregnancy per embryo transfer of dairy heifer recipients of embryos produced in vitro

The objective of this experiment was to evaluate effects of supplemental progesterone immediately following transfer of frozen-thawed, IVP embryos on P/ET. Holstein heifers (n = 452), allocated to nine transfer groups over time, were assigned to be embryo recipients in a completely randomized study from December 2016 to April 2017. All heifers were randomly assigned to one of two treatments: 1) control (CON; n = 212) with no further treatment, or 2) received a CIDR insert containing progesterone for 12 d, beginning on the day of transfer (D 7) and removed 12 d later on Day 19 (CIDR; n = 228). A subset of heifers were subjected to blood sampling on Day 7 (ET) and Day 19 (CIDR removal) to determine circulating concentrations of progesterone. Pregnancy was initially determined using a serum assay for pregnancy specific protein-B at approximately Day 40 after ET and confirmed a month later using trans-rectal ultrasonography. Overall, P/ET did not differ (P =  0.941) between treatment groups. At the initial pregnancy determination, P/ET differed (P =  0.007) among transfer groups. Concentrations of progesterone tended to be less (P =  0.064) in heifers in the CON group compared to heifers treated with the CIDR (3.6 ± 0.27 compared with 4.4 ± 0.27 ng/mL), and differed between transfer groups (P <  0.001) and days post-estrus (P =  0.019) of the recipients. In summary, while treatment with supplemental progesterone at the time of transfer of IVP embryos using a CIDR increased circulating progesterone, there was no influence on P/ET.

Live-cell imaging of nuclear-chromosomal dynamics in bovine in vitro fertilised embryos

Nuclear/chromosomal integrity is an important prerequisite for the assessment of embryo quality in artificial reproductive technology. However, lipid-rich dark cytoplasm in bovine embryos prevents its observation by visible light microscopy. We performed live-cell imaging using confocal laser microscopy that allowed long-term imaging of nuclear/chromosomal dynamics in bovine in vitro fertilised (IVF) embryos. We analysed the relationship between nuclear/chromosomal aberrations and in vitro embryonic development and morphological blastocyst quality. Three-dimensional live-cell imaging of 369 embryos injected with mRNA encoding histone H2B-mCherry and enhanced green fluorescent protein (EGFP)-α-tubulin was performed from single-cell to blastocyst stage for eight days; 17.9% reached the blastocyst stage. Abnormalities in the number of pronuclei (PN), chromosomal segregation, cytokinesis, and blastomere number at first cleavage were observed at frequencies of 48.0%, 30.6%, 8.1%, and 22.2%, respectively, and 13.0%, 6.2%, 3.3%, and 13.4%, respectively, for abnormal embryos developed into blastocysts. A multivariate analysis showed that abnormal chromosome segregation (ACS) and multiple PN correlated with delayed timing and abnormal blastomere number at first cleavage, respectively. In morphologically transferrable blastocysts, 30-40% of embryos underwent ACS and had abnormal PN. Live-cell imaging may be useful for analysing the association between nuclear/chromosomal dynamics and embryonic development in bovine embryos.

Review: Applications and benefits of sexed semen in dairy and beef herds

The use of sexed semen in dairy and beef cattle production provides a number of benefits at both farm and industry levels. There is an increasing demand for dairy and beef products across the globe, which will necessitate a greater focus on improving production efficiency. In dairy farming, there is surplus production of unwanted male calves. Male dairy calves increase the risk of dystocia compared with heifer calves, and as an unwanted by-product of breeding with conventional semen, they have a low economic value. Incorporating sexed semen into the breeding programme can minimise the number of unwanted male dairy calves and reduce dystocia. Sexed semen can be used to generate herd replacements and additional heifers for herd expansion at a faster rate from within the herd, thereby minimising biosecurity risks associated with bringing in animals from different herds. Furthermore, the use of sexed semen can increase herd genetic gain compared with use of non-sorted semen. In dairy herds, a sustainable breeding strategy could combine usage of sexed semen to generate replacements only, and usage of beef semen on all dams that are not suitable for generating replacements. This results in increased genetic gain in dairy herd, increased value of beef output from the dairy herd, and reduced greenhouse gas emissions from beef. It is important to note, however, that even a small decrease in fertility of sexed semen relative to conventional semen can negate much of the economic benefit. A high fertility sexed semen product has the potential to accelerate herd expansion, minimise waste production, improve animal welfare and increase profitability compared with non-sorted conventional semen.