Semen sexing and its impact on fertility and genetic gain in cattle.

Semen sexing is among one of the most remarkable inventions of the past few decades in the field of reproductive biotechnology. The urge to produce offspring of a desired sex has remained since traditional times. Researchers have tried many methods for accurate semen sexing, but only the flow cytometry method has proved to be effective for commercial utilization. However, there were always concerns about the effects of sexed semen, especially on fertility and the rate of genetic gain. Some concerns were genuine because of factors such as low semen dosage in sexed semen straws and damage to sperm during the sorting process. Various researchers have conducted numerous studies to find out the effect of sexed semen on fertility and, in this article, we reflect on their findings. Initially, there were comparatively much lower conception rates (∼70% of conventional semen) but, with refinement in technology, this gap is bridging and the use of sexed semen will increase over time. Concerning genetic gain with use of sexed semen, a positive effect on rate of genetic progress with the use of sexed semen has been observed based on various simulation studies, although there has been a mild increase in inbreeding.

Sperm quality variables of sex-sorted bull semen produced by magnetic-activated cell sorting coupled with recombinant antibodies targeting Y-chromosome-bearing sperm.

The immunological sexing method using antibodies offers cost-effective, high-volume production but faces challenges in terms of X-sperm purity in sexed semen. This research aimed to produce sexed bull semen using highly specific recombinant antibodies in magnetic-activated cell sorting (MACS), evaluate sperm quality and kinematic parameters, and verify the sex ratio of sperm, embryos, and live calves. Fresh semen from two Angus bulls was separated into two equal groups: conventional (CONV) semen and semen sexed using MACS with Y-scFv antibody conjugation to separate two fractions, i.e., the X-enriched and Y-enriched fractions. Then, computer assisted semen analysis and imaging flow cytometry were used to evaluate sperm motility and kinematic variables, acrosomal integrity, sperm viability, and sperm sex ratios. The results showed that sperm motility and quality did not differ between X-enriched and CONV semen. However, the Y-enriched fraction showed significantly lower sperm quality than the X-enriched fraction and CONV semen. The sperm ratio revealed that X-sperm accounted for up to 79.50% of the X-enriched fraction, while Y-sperm accounted for up to 78.56% of the Y-enriched fraction. The sex ratio of embryos was examined using in vitro fertilization. The cleavage rates using CONV and X-enriched semen were significantly higher than that using Y-enriched semen. Accordingly, 88.26% female blastocysts were obtained by using X-enriched semen, and 83.58% male blastocysts were obtained by using Y-enriched semen. In farm trials, 304 cows were subjected to AI using X-enriched and CONV semen. The pregnancy rate did not differ between the X-enriched and CONV semen groups. On the other hand, X-enriched semen generated significantly more live female calves (83.64%) than CONV semen (47.00%). The MACS sexing method significantly enhanced the X-sperm purity in sexed semen, producing high-quality sperm, a high percentage of female blastocytes, and a high percentage of live female calves.

New insights from poly-lactic acid and ionomer films coupled with recombinant antibodies for processing sexed-sorting bovine sperm.

In this study, the efficacy of ionomers and poly-lactic acid (PLA) as an alternative solid material combined with scFv antibodies specific to bovine Y-sperm (Y-scFv) was studied to create a novel method of sexing technology. The coupling efficiency of Y-scFv to the surface of PLA, Na+ and Zn2+ ionomer film was between 2 and 8 mg/mL. Fourier transform infrared spectra confirm that Y-scFv was bound with a carboxylic acid group in each film. Therefore, Na+, Zn2+ ionomers and PLA films conjugated with 4 and 8 mg/mL Y-scFv showed the highest concentration of Y-sperm in the eluted fraction. Considering that the elute fraction was enriched Y-sperm fraction, it contained 67.70-77.94 % of the Y-sperm ratio related to the produced supernatant fraction, which contained up to 69.31-76.01 % enriched X-sperm. In addition, the sperm quality after the sexing process was analyzed by CASA and imaging flow cytometry, which showed that each polymer did not have a negative effect on sperm motility and acrosome integrity for X-sperm. The capacity of ionomer and PLA combined with Y-scFv are used for bovine sperm sexing.

Evaluation of sexed semen-based artificial insemination in Tharparkar cattle under organized farm condition.

Sexed semen facilitates additional female calf production for the expansion of a herd at a faster rate and also curtails the surplus production of unwanted male calves. A study was conducted to evaluate the performance of sexed semen in indigenous Tharparkar cows based on 114 artificial inseminations (AI) performed at natural oestrus using two protocols i.e., single AI (n = 48) and double AI (n = 66). Overall, the first service conception rate (CR) was significantly higher in double (53.0%) than single (33.3%) AI protocol. The odds ratio of conception rate in double AI was 2.26 (χ2 = 4.4, df = 1, p = .04) with respect to single AI. The time that elapsed since the detection of oestrus to insemination was also analysed. In a single AI protocol, the CR was higher (p < .05) at 16 h (54.6%) than insemination at 8 h (27.0%) following the onset of oestrus. Yet, the CR using double AI protocol did not differ (p = .73) significantly when AIs were performed either at 8 h and 24 h (51.9%) or 16 h and 24 h (57.1%) post onset of oestrus. Besides, like the single AI protocol, the parity of the animals also influenced the CR, being higher in heifers (n = 22) than those of parous (n = 92) cows (72.73 vs. 40.43%, χ2 = 7.48, df = 1, p = .006) in the present study. The odds ratio of conception in heifers was 3.93 with respect to parous cows. Overall, the birth of female calf was 91.7%. In conclusion, the present study indicates a future promise of the sexed semen for the production of more female offspring from Tharparkar cattle.

Biochemical Features of X or Y Chromosome-Bearing Spermatozoa for Sperm Sexing.

This review presents information on biochemical features of spermatozoa bearing X or Y chromosome, enabling production of a sperm fraction with pre-defined sex chromosome. The almost only technology currently used for such separation (called sexing) is based on the fluorescence-activated cell sorting of sperm depending on DNA content. In addition to the applied aspects, this technology made it possible to analyze properties of the isolated populations of spermatozoa bearing X or Y chromosome. In recent years, existence of the differences between these populations at the transcriptome and proteome level have been reported in a number of studies. It is noteworthy that these differences are primarily related to the energy metabolism and flagellar structural proteins. New methods of sperm enrichment with X or Y chromosome cells are based on the differences in motility between the spermatozoa with different sex chromosomes. Sperm sexing is a part of the widespread protocol of artificial insemination of cows with cryopreserved semen, it allows to increase proportion of the offspring with the required sex. In addition, advances in the separation of X and Y spermatozoa may allow this approach to be applied in clinical practice to avoid sex-linked diseases.

Sorted Bulls' X-Chromosome-Bearing Spermatozoa Show Increased GAPDHS Activity Correlating with Motility.

Sperm sexing is a technique for spermatozoa sorting into populations enriched with X- or Y-chromosome-bearing cells and is widely used in the dairy industry. Investigation of the characteristics of sorted semen is of practical interest, because it could contribute to the enhancement of sexed semen fertility characteristics, which are currently lower than those of conventional semen. Comparison of a spermatozoa population enriched with X-chromosome-bearing cells to a mixed population is also intriguing in the context of potential differences that drive the mechanisms of primary sex-ratio determination. In this work, sexed (X spermatozoa) and conventional spermatozoa of Holstein bulls were analyzed for the content and enzymatic activity of GAPDHS, a sperm-specific isoform of glyceraldehyde-3-phosphate dehydrogenase that plays a significant role in the regulation of flagellar activity. No difference in the amount of this glycolysis enzyme per cell was revealed, but, notably, GAPDHS enzymatic activity in the sexed samples was significantly higher. Enzymatic activity among the group of sexed but not conventional sperm samples positively correlated with spermatozoa motility, which indicates the significant role of this enzyme for the sorted cells population.

Applications and world-wide use of sexed semen in cattle.

Successful sorting of sperm based on presence of the X- or Y-chromosome was first reported in the early 1980's with the first live births reported in rabbits in 1988. Subsequent development of technological efficiencies resulted in commercialization of sex-sorted semen to cattle producers in 2003-2005. At product launch, low throughput dictated that reasonable prices to the producer could only be accomplished with extremely low sperm number dosages (2 × 106). Furthermore, conception rates were 70%-75% of those achieved by conventional unsorted product. Refinements in sorting equipment have enhanced the number of sperm that can be sorted from a semen sample and (or) aliquot of time, which translates into reduced production costs, while modifications to other aspects of sperm processing and freezing have facilitated maintenance of a conception potential more similar to that of conventional semen. More recently, strategic use of sex-sorted semen coupled with genomic technologies to identify superior females to satisfy replacement female needs has, by default, led to identification of a population of dairy cows from which replacements are not desired, leading to a tremendous increase in use of beef semen in dairy herds. Though exact numbers are unavailable, estimates indicate sex-sorted semen is rapidly approaching 30% of the total AI market share in North America. Though the primary application of sex-sorted semen is to accelerate genetic progress while enhancing biosecurity through in-house production of replacement animals, numerous other potential applications are evolving or are under consideration.

Exploiting a Y chromosome-linked Cas9 for sex selection and gene drive.

CRISPR-based genetic engineering tools aimed to bias sex ratios, or drive effector genes into animal populations, often integrate the transgenes into autosomal chromosomes. However, in species with heterogametic sex chromsomes (e.g. XY, ZW), sex linkage of endonucleases could be beneficial to drive the expression in a sex-specific manner to produce genetic sexing systems, sex ratio distorters, or even sex-specific gene drives, for example. To explore this possibility, here we develop a transgenic line of Drosophila melanogaster expressing Cas9 from the Y chromosome. We functionally characterize the utility of this strain for both sex selection and gene drive finding it to be quite effective. To explore its utility for population control, we built mathematical models illustrating its dynamics as compared to other state-of-the-art systems designed for both population modification and suppression. Taken together, our results contribute to the development of current CRISPR genetic control tools and demonstrate the utility of using sex-linked Cas9 strains for genetic control of animals.

Short-term storage of semen samples in acidic extender increases the proportion of females in pigs.

BACKGROUND: Sex preselection is a desired goal of the animal industry to improve production efficiency, depending on industry demand. In the porcine industry, there is a general preference for pork from female and surgically castrated male pigs. Therefore, the birth of more females than males in a litter leads to economic benefits and improved animal welfare in the pig production industry. Our previous study suggested that the porcine semen extender (BTS) adjusted to pH 6.2 maximises the differences in viability between X-chromosome-bearing (X) spermatozoa and Y-chromosome-bearing (Y) spermatozoa without affecting sperm's functional parameters. In this study we aimed to evaluate whether the pH 6.2 extender is applicable at the farm level for increasing the number of female piglets without a decline in spermatozoa fertility. Artificial insemination (AI) was carried out with spermatozoa stored at pH 6.2 and pH 7.2 (original BTS) at day 1 and day 2 of storage. Next, the functional parameters of the spermatozoa, litter size, farrowing rate, and female-to-male ratio of offspring were determined. RESULTS: Although sperm motility decreased significantly after 2 d of storage, the viability of spermatozoa was preserved at pH 6.2 for 3 d. There was no significant difference in the farrowing rate and average litter size between the group inseminated with the spermatozoa stored in (pH 7.2) and that inseminated with spermatozoa stored in acidic BTS. The percentage of female piglets was approximately 1.5-fold higher in sows inseminated on day 1 in the pH 6.2 than in the pH 7.2 group. Furthermore, although there was no significant difference in the female-to-male ratio, the percentage of female piglets born was slightly higher in the pH 6.2 group than in the pH 7.2 group on day 2. CONCLUSIONS: The method optimised in our study is simple, economical, and may enhance the number of female births without any decline in spermatozoa fertility.

Comparison of pregnancy per AI of heifers inseminated with sex-sorted or conventional semen after oestrus detection or timed artificial insemination.

The objective of the study was to compare the fertility after using sex-sorted or conventional semen either with oestrus detection (EST) or timed artificial insemination (TAI) in Holstein heifers. Holstein heifers were randomly assigned to one of the following treatments in a 2 × 2 factorial design. Heifers in the EST group were inseminated with sex-sorted (n = 114) or conventional semen (n = 100) after spontaneous or induced oestrus. Heifers in the TAI, subjected to the 5-day Cosynch+Progesterone protocol (GnRH+P4 insertion-5d-PGF2α +P4 removal-1d-PGF2α -2d-GnRH+TAI), were inseminated with sex-sorted (n = 113) or conventional semen (n = 88). Statistical analyses were performed using PROC GLIMMIX procedure of SAS 9.4 (SAS Institute Inc., Cary, NC). Overall P/AI was 60.7% for EST and 54.2% for TAI regardless of types of semen and 68.1% for conventional and 48.9% for sex-sorted semen regardless of insemination strategies. Fertility of heifers inseminated with either sex-sorted (53.5%; 44.2%) or conventional (69.0%; 67.0%) semen did not differ between EST and TAI respectively. Besides, the interaction between the semen type and the insemination strategy was not significant for P/AI. The embryonic loss was significantly greater with sex-sorted semen (17.1%) compared to conventional semen (1.6%). There was no sire effect with sex-sorted semen on P/AI (52.6% vs. 46.2%) and embryonic loss (16.4% vs. 18.0%). As expected, sex-sorted semen resulted in more female calves (89.8% vs. 51.6%) than conventional semen. Thus, sex-sorted semen can be used with 5-day Cosynch+Progesterone protocol to eliminate the inadequate oestrus detection and to increase female calves born in dairy heifers.

Disparities among infertility patients regarding genetic carrier screening, sex selection, and gene editing.

PURPOSE: The purpose of this study is to evaluate the perspectives of infertility patients regarding genetic carrier screening, embryo sex selection, embryo research, and gene editing. METHODS: An anonymous 32-question survey was distributed electronically to all patients who seen at a single academic fertility center for at least one visit between June 2018 and September 2019. Survey questions evaluated patient perspectives on genetic carrier screening, embryo sex selection, embryo research, and gene editing. RESULTS: There were 1460 survey responses (32.0% response rate). There were significant differences in the proportion of respondents receiving genetic carrier screening between racial groups, 73.1% of White, 45.5% of Black, 49.4% of Hispanic, and 62.8% of Asian respondents. The likelihood of having genetic carrier screening was also significantly influenced by respondent income, insurance status, and religion. Religion significantly influenced the acceptance of embryonic research and embryonic sex selection. While only 8.9% felt that genetically modifying embryos for physical traits should be allowed, 74.1% felt that genetic modification to correct disease should be allowed. CONCLUSION: Racial, religious, and socioeconomic factors significantly impacted respondents' likelihood to have genetic carrier screening and views on embryo sex selection, embryo research, and gene editing. These findings highlight the importance of tailoring genetic counseling to the individual, acknowledging individual and cultural differences in agreement with genetic testing and emerging genetic therapies.

Bovine semen sexing: Sperm membrane proteomics as candidates for immunological selection of X- and Y-chromosome-bearing sperm.

The use of sexed semen in dairy and beef farms ensures the production of animals of the desired sex, resulting in a reduction of costs and an improvement of environmental sustainability. Several methods have been developed over the years, but most of them were abandoned due to their limited efficacy. Currently, the only commercially available method for the separation of X- and Y-chromosome-bearing sperm is fluorescence-activated cell sorting. However, this technique is expensive and has limited usefulness for the industry, considering that it cannot produce doses of sexed semen with the desired number of sperm for artificial insemination. Immunological methods have emerged as an attractive alternative to flow cytometry and proteomic knowledge of X- and Y-sperm could be useful to the development of a new method. In this review, we identify the main applications of sexed semen, describe the existing methods and highlight future research opportunities in the field. We consider that immunological methods, based on sperm cell's surface proteins differentially expressed between X- and Y-sperm, could be an interesting and promising approach to semen sexing.

Production of sexed bovine embryos in vitro can be improved by selection of sperm treatment and co-culture system.

The study investigated the effects of sperm sorting, capacitation treatment and co-cultivation on sexed bovine in vitro embryo production. The effect of treatment and co-culture on production of embryos of the preferred sex from unsorted sperm was also studied. Sperm from five breeding bulls was used for fertilization of mature oocytes as follows: Experiment 1, sorted and unsorted sperm (bulls A-E) treated only with heparin in standard co-cultures; Experiment 2, sorted sperm (bulls A-E) treated with heparin-PHE (penicillamine, hypotaurine, and epinephrine) or heparin-caffeine in drop co-cultures; and Experiment 3, unsorted sperm (bull E) treated with either heparin-PHE or heparin-caffeine in both standard and drop co-cultures. In all bulls, treatment with heparin resulted in significantly (p < .05) reduced cleavage and blastocyst rates from sorted sperm, as compared with those from unsorted sperm. In bulls A, B, D and E, treatment of sorted sperm with heparin-PHE in drops significantly increased the blastocyst rate (p < .05). In unsorted sperm of bull E, heparin-PHE treatment in drops resulted in the XX/XY sex ratio inverse to that obtained by heparin-caffeine treatment in standard co-cultures (32.3%/67.7% and 66.7%/33.3%, respectively). In conclusion, the treatment of sorted sperm with heparin-PHE in modified drop co-cultures can be recommended for production of in vitro sexed embryos. The use of unsorted sperm for production of embryos of the preferred sex by selected capacitation treatment and co-culture can be the method of choice in bulls with low IVF yields from sorted sperm.

Recovery of sperms bearing X chromosomes with different concentrations of magnetic nanoparticles in ram.

Pre-conceptual sex selection is still a highly debatable process whereby X and Y chromosome bearing spermatozoa are isolated before oocyte fertilization. Recently, magnetic nanoparticles (MNP) have been used to determine X and Y chromosomes bearing spermatozoa as a result of searching for a cheap, highly efficient method using non-toxic materials. This study aimed to recover the sperm bearing X chromosomes in ram with different concentrations of MNP and then evaluate the success of this method using polymerase chain reaction (PCR). Ram sperms were divided into four groups, treated with 0 (control), 50, 100 and 200 µg/ml MNP, respectively. MNP was used to restore sperm cells bearing X chromosomes. Upon recovery, the PCR was performed to identify the X and Y sperms, Methyl ThiazoleTetrazolium (MTT), to assess MNP toxicity and sperm viability and acridine orange (AO) to evaluate sperm DNA integrity. The results of PCR revealed that the treatment of spermatozoa- bearing X chromosomes with 50 µg/ml MNP had the highest effects on the recovery of X sperm rather than the other concentrations of MNP. However, the concentrations of MNP did not have any toxic effects on spermatozoa, sperm viability and, DNA integrity, but the high concentration of MNP (200 µg/ml) significantly reduced DNA integrity. According to MTT and AO results, the concentrations of MNP used in this study had no toxic effects on spermatozoa and did not reduce the sperm viability and DNA integrity, except that 200 µg/ml MNP significantly reduced DNA integrity.

New technique of sex preselection for increasing female ratio in boar sperm model.

In this study, we tried to optimize the porcine semen extender conditions to maximize the differences between live X chromosome-bearing (X) spermatozoa and to Y chromosome-bearing (Y) spermatozoa without a decline in the fertility rate at different pH conditions during storage. We observed the viability of X and Y boar spermatozoa in acidic (pH 6.2), original (pH 7.2), and alkaline condition (pH 8.2) for 5 days to investigate the effect of storage conditions on the X to Y spermatozoa ratio. The functional parameters of spermatozoa were also examined to evaluate sperm quality. Sperm motility was preserved at pH 7.2 and pH 6.2 for 3 days, while sperm motility at pH 8.2 decreased significantly after 2 days. Non-capacitated spermatozoa increased while capacitated spermatozoa decreased during storage. Sperm viability decreased significantly duration-dependent under all pH conditions, but there was no significant difference during storage at pH 6.2 and 7.2. The X: Y ratio of live spermatozoa in acidic condition was maximized (1.2:1) without affecting the sperm function and fertility-related protein expression after 2 days compared to original conditions. Moreover, insemination of sows using acidic extender increased the number of female pups on days 1 and 2 of preservation. These results indicate that the production of female offspring may increase when acidic BTS is used for 2 days without affecting the success rate of AI. Above all, this method is simple and economical compared to other methods.

Production of monoclonal antibody against recombinant bovine sex-determining region Y (SRY) and their preferential binding to Y chromosome-bearing sperm.

Separation of X and Y chromosome-bearing sperm is an appropriate method for the selection of desired sex of offspring to increase the profit in livestock industries. The purpose of this study was the production of a monoclonal antibody against recombinant bovine sex-determining region Y protein for separation Y sperm. The hybridoma cells from splenocytes of immunized female's balb/C mice and Sp2/0 cells were made. The binding affinity of our monoclonal antibody (mAbSRY2) was compared with mouse monoclonal SRY-15. The Western blot method indicated that mAbSRY2 successfully detected the rbSRY protein. The specificity and sensitivity of mAbSRY2 is comparable to SRY-15 commercially ones. The SRY gene in 100% of bull semen contains the Y chromosome that had the strongest binding affinity to mAbSRY2 was synthesized. In other words, the binding affinity of semen contains the X sperms near the negative control. In general, this immunological method can help to separate X from Y sperms. However, the mAbSRY2 is bind to Y-bearing sexed sperm, but in the future; the sexed sperms need to apply in farms.

A simple sperm-sexing method that activates TLR7/8 on X sperm for the efficient production of sexed mouse or cattle embryos.

The preferred sex of livestock differs among breeders; for example, dairy farmers prefer female calves for the production of milk, whereas cattle meat producers often prefer males. Sexing of laboratory animals is also beneficial in some research fields, including reproductive biology and metabolic studies. Most sexing methods separate X sperm and Y sperm with a cell sorter. Here, we describe a system in which treatment with the TLR7/8 ligand (R848) separates X sperm from Y sperm. Because this protocol does not require any special equipment or professional skills, it can be easily applied in laboratories where in vitro fertilization (IVF) is performed. The sperm are treated with 0.03 µM R848 in 1 mL of modified human tubal fluid (mHTF) medium (mouse sperm) or 3 mL of mHTF medium (bull sperm) for 60 min, and then the upper layer (400 µL in mouse sperm or 1 mL in bull sperm) and the precipitate are separately collected. After each sample is washed by centrifugation, the sperm are suspended in ligand-free IVF medium and can then be used for IVF. More than 90% of the embryos made with upper-layer sperm are XY in both mice and cattle, and >80% of the embryos made with precipitated sperm are XX in both species. Separation of X sperm and Y sperm for IVF can be completed within 2 h.

Publicity, politics, and professoriate in fin-de-siècle Vienna: The misconduct of the embryologist Samuel Leopold Schenk.

This essay uses the case of the fin-de-siècle Vienna embryologist Samuel Leopold Schenk to analyze the factors at play in allegations of misconduct. In 1898, Schenk published a book titled Theorie Schenk. Einfluss auf das Geschlechtsverhältnis (Schenk's theory. Influence on the sex ratio). The book argued that, by changing their diet, women trying to conceive could influence egg maturation and consequently select the sex of their offspring. This cross between a scientific monograph and a popular advice book received enormous publicity but also spurred first the Vienna Medical Association and then the Senate of the University of Vienna to accuse Schenk of poor science, self-advertisement, quack medical practice, and wrong publisher choice. Formal proceedings against Schenk ended in 1900 with the unusually harsh punishment of early retirement. Schenk died two years later. I examine the elements of the case, from the science of sex determination and selection, to the growth of print media and advertising within the changing demographic and political landscape of Vienna. I argue that the influence of the public, via the growing media, upon science was the main driver of the case against Schenk, but also that the case would have had a more limited impact were it not for the volatile political moment rife with anti-Semitism, nationalism, and xenophobia. I draw the attention to the importance of setting cases of misconduct in the broader political history and against the key social concerns of the moment.

A fly model establishes distinct mechanisms for synthetic CRISPR/Cas9 sex distorters.

Synthetic sex distorters have recently been developed in the malaria mosquito, relying on endonucleases that target the X-chromosome during spermatogenesis. Although inspired by naturally-occurring traits, it has remained unclear how they function and, given their potential for genetic control, how portable this strategy is across species. We established Drosophila models for two distinct mechanisms for CRISPR/Cas9 sex-ratio distortion-"X-shredding" and "X-poisoning"-and dissected their target-site requirements and repair dynamics. X-shredding resulted in sex distortion when Cas9 endonuclease activity occurred during the meiotic stages of spermatogenesis but not when Cas9 was expressed from the stem cell stages onwards. Our results suggest that X-shredding is counteracted by the NHEJ DNA repair pathway and can operate on a single repeat cluster of non-essential sequences, although the targeting of a number of such repeats had no effect on the sex ratio. X-poisoning by contrast, i.e. targeting putative haplolethal genes on the X chromosome, induced a high bias towards males (>92%) when we directed Cas9 cleavage to the X-linked ribosomal target gene RpS6. In the case of X-poisoning sex distortion was coupled to a loss in reproductive output, although a dominant-negative effect appeared to drive the mechanism of female lethality. These model systems will guide the study and the application of sex distorters to medically or agriculturally important insect target species.

Comparison between in vitro embryo production using Y-sorted sperm and timed artificial insemination with non-sorted sperm to produce crossbred calves.

Due to the increasing use of in vitro embryo production (IVEP) and the importance of crossbreeding for beef production, pregnancy rates of Nelore recipients were evaluated following Fixed Time Embryo Transfer with fresh or vitrified IVEP embryos produced with Y-sorted sperm of Angus bulls (B. taurus) or Fixed Time Artificial Insemination using non-sorted sperm. For IVEP in Experiment 1, oocytes were obtained using Ovum Pick Up (OPU) (n = 84 embryos) or from ovaries from a slaughterhouse (SLAUGHTER, n = 66 embryos). In Experiment 2, with oocytes obtained by OPU, IVEP embryos were fresh (FRESH, n = 271) or after vitrification/warming (VITRIFIED, n = 79) and PR was compared with FTAI (n = 239). In Experiment 1, cleavage rates were 63.8% and 39.1% for OPU and SLAUGHTER groups, respectively (P = 0.02), and blastocyst rates were 30.5% and 14.7%, respectively (P = 0.09). The PR was similar when considering the source of oocytes (OPU = 35.7%; SLAUGHTER = 25.8%; P = 0.17). In Experiment 2, there was no difference in PR for FRESH or VITRIFIED embryos (34.3% and 30.4%, respectively, P = 0.72), but lesser than FTAI (47.7, P = 0.002). It is concluded that the IVEP with Y-sorted sperm associated with vitrification or embryos produced with oocytes from different sources did not affect PR when there was transfer of crossbred embryos into recipients, and can optimize large-scale application of IVEP technology; however, FTAI pregnancy rates with non-sex sorted sperm were greater.