Effect of sex sorting on CTC staining, actin cytoskeleton and tyrosine phosphorylation in bull and boar spermatozoa

Seminal extracellular vesicles alter porcine in vitro fertilization outcome by modulating sperm metabolism

Porcine seminal plasma (SP) is loaded with a heterogeneous population of extracellular vesicles (sEVs) that modulate several reproductive-related processes. This study investigated the effect of two sEV subsets, small (S-sEVs) and large (L-sEVs), on porcine in vitro fertilization (IVF). The sEVs were isolated from nine SP pools (five ejaculates/pool) using a size-exclusion chromatography-based procedure and characterized for quantity (total protein), morphology (cryogenic electron microscopy), size distribution (dynamic light scattering), purity and EV-protein markers (flow cytometry; albumin, CD81, HSP90β). The characterization confirmed the existence of two subsets of high purity (low albumin content) sEVs that differed in size (S- and L-sEVs). In vitro fertilization was performed with in vitro matured oocytes and frozen-thawed spermatozoa and the IVF medium was supplemented during gamete coincubation (1 h at 38.5 °C, 5 % CO2 in a humidified atmosphere) with three different concentrations of each sEV subset: 0 (control, without sEVs), 0.1, and 0.2 mg/mL. The first experiment showed that sEVs, regardless of subset and concentration, decreased penetration rates and total IVF efficiency (P < 0.0001). In a subsequent experiment, it was shown that sEVs, regardless of subset and concentration, impaired the ability of spermatozoa to bind to the zona pellucida of oocytes (P < 0.0001). The following experiment showed that sEVs, regardless of the subset, bound to frozen-thawed sperm but not to in vitro matured oocytes, indicating that sEVs would affect sperm functionality but not oocyte functionality. The lack of effect on oocytes was confirmed by incubating sEVs with oocytes prior to IVF, achieving sperm-zona pellucida binding results similar to those of control. In the last experiment, conducted under IVF conditions, sperm functionality was analyzed in terms of tyrosine phosphorylation, acrosome integrity and metabolism. The sEVs, regardless of the subset, did not affect sperm tyrosine phosphorylation or acrosome integrity, but did influence sperm metabolism by decreasing sperm ATP production under capacitating conditions. In conclusion, this study demonstrated that the presence of sEVs on IVF medium impairs IVF outcomes, most likely by altering sperm metabolism.

Extracellular cAMP and MRP4 activity influence in vitro capacitation and fertilizing ability of pig spermatozoa

cAMP has been reported to be an essential driver of sperm capacitation. In bovine sperm cAMP efflux through multidrug resistance-associated protein 4 (MRP4) has been suggested to maintain intracellular cAMP homeostasis and generate extracellular signaling able to regulate capacitation. The aim of this work was to determine whether extracellular cAMP may influence in vitro pig sperm capacitation and acquisition of fertilizing ability and to evaluate the role of MRP4. In vitro sperm capacitation and gamete coincubation were performed in Brackett and Oliphant's medium (BO) in presence of caffeine (Ctr+) or in BO without caffeine (Ctr-) supplemented with 0, 8, 9, 10 mM cAMP. Despite the percentage of capacitated sperm, assayed by immunolocalization of tyrosine-phosphorylated proteins, was significantly lower in Ctr- compared to Ctr+, it increased supplementing 10 mM cAMP to Ctr- reaching values similar to Ctr+. The absence of caffeine during gamete coincubation reduced the fertilization rate compared to Ctr+, while 10 mM cAMP supplementation to Ctr- increased the fertilization rate reaching values similar to Ctr + . The presence of MRP4 in pig spermatozoa was detected for the first time by western blot and immunohistochemistry assays. To evaluate MRP4 role on pig sperm capacitation, in vitro capacitation and gamete coincubation were performed in Ctr + in presence of MK571, a MRP4 selective inhibitor. MK571 reduced the percentage of capacitated cells and the fertilization rate, while cAMP addition fully reversed MRP4 blockade consequences. Present findings suggest that, under our in vitro conditions, extracellular cAMP and MRP4 activity influence pig sperm capacitating events.

Expression of aldose reductase in mouse endometrial epithelial cells and its role in sperm capacitation

The survival, motility and capacitation of sperm in the female reproductive tract are important prerequisites for fertilization. The uterus is the main location for sperm capacitation. One of the most important physiological functions of the endometrial epithelium is to create a suitable uterine environment under the regulation of ovarian hormones, to ensure sperm capacitation. The composition of uterine fluid directly affects sperm capacitation. Fructose is an important component of semen that supports sperm viability and motility. Aldose reductase, a rate-limiting enzyme in the polyol pathway, metabolizes sorbitol and fructose, thereby supplying cells with necessary energy for functional activities. Existing studies have reported the presence aldose reductase in the endometrium, leading us to hypothesize that its expression in endometrial epithelium might promote sperm capacitation by maintaining the uterine environment. Yet, the mechanism of regulation has not been clarified. In this study, we investigated the expression of aldose reductase in mouse endometrial epithelium and its potential role in sperm capacitation. We initially investigated the periodic characteristics of glucose, fructose and sorbitol in uterine fluid. We then studied the temporal and spatial characteristics of aldose reductase in the endometrial epithelium. Next, we examined the effect of aldose reductase on glucose, fructose and sorbitol in uterine fluid. Finally, we explored the effect of aldose reductase on sperm capacitation and fertilization. The results showed that glucose and fructose content in uterine fluid and the expression of aldose reductase fluctuated periodically during physiological periods. Inhibition of aldose reductase in the endometrial epithelium interfered with sperm capacitation and fertilization by reducing the fructose levels in the uterine fluid. To conclude, the aldose reductase-mediated polyol pathway in endometrial epithelial cells is essential to maintain an appropriate fructose environment in the uterine fluid for sperm capacitation and fertilization.

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.

Differential Membrane Protein Profile in Bovine X- and Y-Sperm

The aim of this study was to understand the molecular mechanisms behind the biological differences of X- and Y-sperm and to screen the sex-specific candidate antigen proteins for sexed semen production. To this end, we investigated differential expression of total membrane proteins of the two sperm types by using high-purity X- and Y-sperm from 20 Holstein bulls and applying the label-free proteomic technique; 1521 proteins were identified. In the X-sperm group, 8 and 23 proteins were significantly up- and down-regulated, respectively. In the X- and the Y-sperm group, 151 and 88 proteins were specifically expressed, respectively. These were overexpressed in the dynamic changes of the actin cytoskeleton, and cell senescence/apoptosis induced by the immune response, and could result in differences in the state, size, and immune sensitivity of the X-/Y-sperm membranes. The prediction of transmembrane structure, subcellular localization, and Western blotting validation results showed that the CLRN3 and SCAMP1 proteins were cell surface specific antigens of X- and Y-sperm, respectively. Our findings help explain the molecular mechanism behind the biological differences of X-/Y-sperm and lay the foundation for application of immunological methods to produce sex-sorted semen and control livestock sex. Data are available via ProteomeXchange with identifier PXD019435.

cDNA cloning, expression and bioinformatical analysis of Tssk genes in tree shrews

Tree shrews are more closely related to primate animals than rodents in many aspects. In addition, they also possess several advantageous characteristics including small body size, high brain-to-body mass ratio, low cost of feeding and maintenance, short reproductive cycle and life span, which make them promising novel laboratory animals to replace more precious larger primate animals. Testis-specific serine/threonine kinase (Tssk) plays important roles in spermatogenesis and/or the regulation of sperm function. However, studies on Tssk in tree shrews have not been reported yet. In the present study, the full-length sequences of five members of the Tssk family in tree shrews were cloned and their CDS region sequences were analyzed by basic bioinformatics. The phylogenetic tree and prokaryotic protein expression system of Tssk gene of tree shrews were constructed. The mRNA expressions of Tssk genes in 11 tissues/organs from tree shrews were studied. The results showed that: 1. the length of the CDS region of tree shrew Tssk gene for Tssk1B, Tssk2, Tssk3 (variant X1 / X2), Tssk4 (variant X1 / X2) and Tssk6 is 1080bp, 1077bp, 867 / 807bp, 1014 / 984bp, 822bp, respectively, encoding 359, 358, 288/268, 337/327 and 273 amino acids, respectively; the cloned sequences of Tssk genes have been submitted to GenBank with the following accession numbers: KX091161(Tssk1B), KX091162(Tssk2), KX091163(Tssk3 variant X1)/KX091164(Tssk3 variant X2), KX091165(Tssk4variant X1)/KX091166(Tssk4variant X2), KX091160(Tssk6). 2. All tree shrew Tssk proteins distribute in cytoplasm, indicating that they are hydrophilic and non-secretory proteins, with multiple phosphorylation sites of serine and/or threonine. In addition, they are all mixed proteins with similar tertiary structures sharing a highly conserved functional domain of S_TKc (Serine/Threonine protein kinases, catalytic domain). 3.The molecular phylogenetic tree of five Tssk genes in tree shrews indicates that they are neither rodent nor primate animal, but are closely related to primate animals. 4. Five members of the Tssk recombinant proteins in tree shrews were successfully obtained using the constructed prokaryotic protein expression system. 5. Five Tssk genes are specifically expressed in the testis and/or sperm of tree shrews. Additionally, small amount of Tssk1B was expressed in several tissues other than testis and sperm. Limited mRNA levels of Tssk2 and Tssk4 were expressed in the brain, while mRNA of Tssk3 or Tssk6 could only be detected in the testis and sperm. This study will provide fundamental data on reproductive biology of tree shrews, which paves a way for further studying Tssk's biological function in this novel model animal.

The micro-RNA content of unsorted cryopreserved bovine sperm and its relation to the fertility of sperm after sex-sorting

BACKGROUND

The use of sex-sorted sperm in cattle assisted reproduction is constantly increasing. However, sperm fertility can substantially differ between unsorted (conventional) and sex-sorted semen batches of the same sire. Sperm microRNAs (miRNA) have been suggested as promising biomarkers of bull fertility the last years. In this study, we hypothesized that the miRNA profile of cryopreserved conventional sperm is related to bull fertility after artificial insemination with X-bearing sperm. For this purpose, we analyzed the miRNA profile of 18 conventional sperm samples obtained from nine high- (HF) and nine low-fertility (LF) bulls that were contemporaneously used to produce conventional and sex-sorted semen batches. The annual 56-day non-return rate for each semen type (NRRconv and NRRss, respectively) was recorded for each bull.

RESULTS

In total, 85 miRNAs were detected. MiR-34b-3p and miR-100-5p were the two most highly expressed miRNAs with their relative abundance reaching 30% in total. MiR-10a-5p and miR-9-5p were differentially expressed in LF and HF samples (false discovery rate < 10%). The expression levels of miR-9-5p, miR-34c, miR-423-5p, miR-449a, miR-5193-5p, miR-1246, miR-2483-5p, miR-92a, miR-21-5p were significantly correlated to NRRss but not to NRRconv. Based on robust regression analysis, miR-34c, miR-7859 and miR-342 showed the highest contribution to the prediction of NRRss.

CONCLUSIONS

A set of miRNAs detected in conventionally produced semen batches were linked to the fertilizing potential of bovine sperm after sex-sorting. These miRNAs should be further evaluated as potential biomarkers of a sire's suitability for the production of sex-sorted sperm.

Short communication: Effect of timing of induction of ovulation relative to timed artificial insemination using sexed semen on pregnancy outcomes in primiparous Holstein cows

Our objective was to determine the effect of increasing the interval from induction of ovulation to timed artificial insemination (TAI) on fertility by decreasing the interval from TAI to ovulation using sexed semen within a synchronized breeding program. Our hypothesis was that induction of ovulation earlier relative to TAI would increase pregnancies per artificial insemination (P/AI). Primiparous Holstein cows from 3 commercial dairy farms in the United States were submitted to a Double-Ovsynch protocol for first service as follows: Pre-Ovsynch (GnRH; 7 d, PGF_2α; 3 d, GnRH), followed 7 d later by Breeding-Ovsynch [GnRH (G1); 7 d, PGF_2α; 24 h, PGF_2α], followed by the last GnRH treatment (G2), which varied between treatments, and TAI. To vary the interval between G2 and TAI, cows were randomized to 2 treatments to receive G2 either 16 (G2-16; n = 373) or 24 (G2-24; n = 357) h before TAI, which was fixed at 48 h after the second PGF_2α treatment of the Breeding-Ovsynch portion of the protocol. All cows were inseminated with sexed semen, and each herd used sires of their choosing, which were randomly allocated between treatments. Pregnancy diagnosis was conducted by herd veterinarians using transrectal ultrasonography. In disagreement with our hypothesis, G2-24 cows had fewer P/AI than G2-16 cows at 34 ± 3 d (44 vs. 50%) and 80 ± 17 d (41 vs. 48%) after TAI. Pregnancy loss (5 vs. 6%) and fetal sex ratio (92:8 vs. 90:10, female:male) did not differ between treatments for G2-16 and G2-24 cows, respectively. Thus, we reject our hypothesis and conclude that induction of ovulation earlier relative to TAI with sexed semen for first service after a Double-Ovsynch protocol decreased P/AI in primiparous Holstein cows.

Proteomic comparison of non-sexed and sexed (X-bearing) cryopreserved bull semen

It is widely recognized that quality of spermatozoa in sexed semen (SS) samples is not as great as for conventional, non-sexed semen (NS). There are differences in qualitative and biochemical variables between spermatozoa in NS and SS. Information, however, is lacking on molecular differences, especially concerning spermatozoa proteomic differences is SS and NS. The objective of this study was to compare commercially available NS and SS bull semen by evaluating sperm quality variables in conjunction with a proteomics approach. Results from flow cytometry and computer-assisted sperm analyses indicated there was less sperm motility, viability, mitochondrial potential and acrosome integrity in sperm from SS. Results from proteomic analysis indicated sperm from NS and SS samples were characterized by different protein profiles. There was identification of 70 sperm proteins that differed in abundance and six protein spots that were different in extent of carbonylation. Sperm from SS had altered structures of enzymes involved in glycolysis, oxidative phosphorylation and maintenance of a constant adenylate energy charge. Furthermore, sperm from SS had alterations of several flagella substructures, especially outer dense fiber proteins, which were less abundant and more carbonylated than in sperm from NS. In sperm of SS, compared with NS, there were differences in abundance of proteins involved in capacitation, acrosome reaction and sperm-egg fusion as well as lesser abundances of sperm surface proteins. Results enable a greater understanding of differences between sperm from NS and SS samples, thereby contributing to development of improved protocols for more effective protection of sexed spermatozoa during processing.

Different approaches for assessing sperm function

Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the "one shot" parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways.

Improvement of in vitro fertilization by a tannin rich vegetal extract addition to frozen thawed boar sperm

Boar spermatozoa are very susceptible to cryopreservation injuries and, for this reason, pig remains one of the few species in which fresh semen is still preferred to thawed one for routine artificial insemination (AI). The present work evaluated the effect of supplementing boar sperm thawing medium with Silvafeed SP (SSP), a mixture of Chestnut and Quebracho wood extracts (60/40 w/w) rich in polyphenols (92.4% tannin content) on in vitro fertilization (IVF) and on the following sperm parameters: sperm motility (assessed by CASA), viability, acrosome integrity, mitochondrial function and lipid peroxidation (assessed by flow cytometry) and capacitation status (immunolocalization of tyrosine phosphorylated proteins). Thawed spermatozoa were incubated 1 h at 37°C in BTS without (CTR) or with (5, 10, 20 µg/mL) SSP. After incubation sperm suspension was divided in three aliquots: one was used for IVF trials, one for sperm analysis, and the last one was capacitated for 1 h at 39°C 5% CO2 in IVF medium. Sperm motility parameters, viability, acrosome integrity, mitochondrial functionality, lipid peroxidation and tyrosine phosphorylated protein immunolocalization, used as capacitation parameter, were not influenced by SSP. However, oocytes inseminated with thawed spermatozoa pretreated with all the different SSP concentrations presented a significant (P < 0.01) increase in penetration rate compared to CTR. In addition, 5 µg/mL SSP exerted a positive effect (P<0.05) on the total efficiency of fertilization. These results encourage the use of SSP in the thawing medium since post-thawing fertility is a limit for the large-scale use of boar frozen semen.

Changes in the Cellular Distribution of Tyrosine Phosphorylation and Its Relationship with the Acrosomal Exocytosis and Plasma Membrane Integrity during In Vitro Capacitation of Frozen/Thawed Bull Spermatozoa

During sperm capacitation, intracellular signaling leads to protein tyrosine phosphorylation (PTP) of multiple cellular structures. However, the connection of this molecular signaling to the physiology of capacitated spermatozoa is not completely understood. This is the case of the short lifespan of capacitated spermatozoa and their increased susceptibility to initiate acrosomal exocytosis (AE) during incubation. Herein, by employing frozen/thawed bull spermatozoa, we aimed to study the relationship between PTP with AE and with plasma membrane integrity (PMI) at the cellular level. For this, we employed double staining following immunofluorescence for PTP combined with fluorescence probes for the acrosome (PNA-FITC) and PMI (LIVE/DEAD Fixable Dead Cell Stain Kit). Our results revealed that the presence of PTP at sperm head was less abundant in the sperm fraction that triggered the AE after 3 h of incubation under capacitating conditions, or by its induction with calcium ionophore, compared to the unreacted fraction. Furthermore, PTP at the equatorial region of the head (PTP-EQ) was enriched in the fraction showing damaged membrane while induction of AE with calcium ionophore did not alter the PMI and its relation to PTP-EQ. These results suggest that spontaneous AE and induced AE trigger similar cellular events regarding PTP and the spermatozoa showing PTP-EQ are more prone to suffer plasma membrane damage.

Optimization of timing of insemination of dairy heifers inseminated with sex-sorted semen

We hypothesized that delaying by approximately 12 h the artificial insemination (AI) of heifers with sex-sorted semen increases pregnancy per AI (P/AI). Holstein heifers (n = 1,207) were fitted with a collar containing an automated estrus-detection device (HR-LDn tags, SCR Engineers Ltd., Netanya, Israel) at 10.7 ± 0.02 mo of age. Once they reached 330 kg, heifers were enrolled in an ovulation synchronization protocol (5-d Cosynch + controlled internal drug release; Zoetis, Parsippany-Troy Hills, NJ). Study personnel recorded the heifers that were in estrus according to the DataFlow II software (SCR Engineers Ltd., Netanya, Israel) twice daily at 0500 and 1500 h from the day of the first PGF_2α (Estrumate; Merck Animal Health, Madison, NJ) injection to 72 h later. Heifers enrolled in the conventional (CONV) and early sex-sorted (SSEarly) semen treatments detected in estrus at 0500 and 1500 h were AI at 0600 and 1600 h of the same day, respectively. Heifers enrolled in the late sex-sorted (SSLate) semen treatment detected in estrus at 0500 and 1500 h were AI at 1600 h of the same day and 0600 h of the following day, respectively. All heifers not detected in estrus by 72 h after the first PGF_2α injection received a GnRH (Fertagyl; Merck Animal Health, Madison, NJ) injection at 0500 h. Heifers in the CONV and SSEarly treatments were AI at fixed time at 0600 h, whereas heifers in the SSLate treatment were AI at fixed time at 1600 h. Among heifers detected in estrus, the ranges of the interval from the onset of estrus to AI were 3.6 to 28.5 h, 0.0 to 25.5 h, and 9.4 to 36.8 h for the CONV, SSEarly, and SSLate treatments, respectively. Among heifers AI at fixed time, the ranges of the interval from the GnRH injection to AI were 0 h for heifers in the CONV and SSEarly treatments and 8.5 to 11.7 h for heifers in the SSLate treatment. The P/AI at 62 ± 1 d after the first AI was greater for CONV (63.1 ± 2.6%) compared with SSEarly (43.3 ± 2.6%) and SSLate (44.8 ± 2.7%). A greater percentage of heifers enrolled in the SSEarly (65.8 ± 2.5%) and SSLate (70.0 ± 2.5%) treatments produced a live female calf compared with the CONV treatment (40.5 ± 2.7%). When the values of 1-d-old female and male calves were USD $0 and the cost of replacement heifers was $750, the cost of raising heifers from enrollment to calving was lesser for the CONV treatment than the SSEarly treatment, but SSLate treatment did not differ from CONV and SSEarly treatments. When the values of a 1-d-old female calf ≥$130 and 1-d-old male calf ≥$30 and the cost of replacement ≥$1,000, no differences were observed among treatments in the cost from enrollment to calving. We conclude from this experiment that the P/AI with sex-sorted semen is not improved when insemination is delayed by approximately 12 h.

Fertility of frozen sex-sorted sperm at 4 × 106 sperm per dose in lactating dairy cows in seasonal-calving pasture-based herds

The objective was to evaluate the reproductive performance of frozen sex-sorted sperm at 4 × 10⁶ sperm per dose (SexedULTRA 4M, Sexing Technologies, Navasota, TX) relative to frozen conventional sperm in seasonal-calving pasture-based dairy cows. Semen from Holstein-Friesian (n = 8) and Jersey (n = 2) bulls was used. Four of the Holstein bulls used were resident at or near a sex-sorting laboratory (Cogent, UK, or ST Benelux, the Netherlands). The remaining 6 bulls were located at studs in Ireland. For these 6 bulls, ejaculates were collected, diluted with transport medium, and couriered to Cogent in parcel shippers. Transit time from ejaculation to arrival at the sorting laboratory was 6 to 7 h. For all bulls, ejaculates were split and processed to provide frozen conventional sperm (CONV) at 15 × 10⁶ sperm per straw and frozen sex-sorted (SS) sperm at 4 × 10⁶ sperm per straw and used to inseminate lactating dairy cows after spontaneous estrus. Pregnancy diagnosis was performed by ultrasound scanning (n = 7,246 records available for analysis). Generalized linear mixed models were used to examine effects on pregnancy per AI (P/AI) at first artificial insemination, with sperm treatment (CONV vs. SS), bull (n = 10), and treatment × bull interaction as the fixed effects, and herd (n = 142) as a random effect. Overall, P/AI was greater for cows inseminated with CONV than for those inseminated with SS (59.9% vs. 45.5%; 76.0% relative to CONV). This study was not designed to compare resident bulls vs. shipped ejaculates, but the magnitude of the difference between P/AI achieved by CONV and SS was apparently less for resident bulls (60.3% vs. 50.2%) than for shipped ejaculates (58.6% vs. 40.7%). We discovered a treatment × bull interaction for shipped ejaculates (P/AI ranged from 45 to 86% relative to CONV) but not for the resident bulls (P/AI ranged from 81 to 87% relative to CONV). Relative P/AI of SS compared with CONV was greater in cows with high or average fertility potential (76.1% and 78.3%, respectively) than in cows with low fertility potential (58.1%). In 33.1% of the enrolled herds, the P/AI achieved with SS was 90% or more of the P/AI achieved with CONV; this was mainly explained by herds in which SS performed exceptionally well but CONV performed poorly. In conclusion, SS had lower overall P/AI compared with CONV; however, P/AI achieved with SS was dependent on the bull, fertility potential of the cow, and herd. Strategies to improve the P/AI with SS in seasonal-calving pasture-based lactating dairy cows require further research.

Bovine sperm sex-selection technology in Japan

BACKGROUND

In Japan, Livestock Improvement Association of Japan started commercially producing sexed bovine semen 10 years ago, and sexed bovine semen is currently used for the artificial insemination (AI) in the farms. In this review, the authors introduce the technology for sperm sexing by flow cytometry, the efforts at commercializing sexed semen in Japan, and recent field data on artificial insemination of the cattle with sexed semen.

METHODS

In the procedures of the flow cytometric method, X-chromosome-bearing sperm and Y-chromosome-bearing sperm were fluorescently stained, separated from each other by analyzing the difference in the DNA content, and cryopreserved. The authors surveyed the conception rates after AI with these sperm and sex ratios of the offspring with the cooperation from livestock associations, AI technicians, and farmers.

MAIN FINDINGS RESULTS

Although AI with sexed semen was associated with lower conception rates in comparison with AI with conventional semen, the accuracy of sex selection using AI with sexed semen was beyond >90%.

CONCLUSION

Sexed semen produced by flow cytometry has the potential to produce offspring of the preferred sex with high accuracy and reliability. Thus, it is expected that sexed semen is used for AI more frequently in the farms.

In vitro characterisation of fresh and frozen sex-sorted bull spermatozoa

This study sought to compare the in vitro characteristics of fresh and frozen non-sorted (NS) and sex-sorted (SS) bull spermatozoa. Experiment 1: Holstein-Friesian ejaculates (n=10 bulls) were split across four treatments and processed: (1) NS fresh at 3×10⁶ spermatozoa, (2) X-SS frozen at 2×10⁶ spermatozoa, (3) X-SS fresh at 2×10⁶ spermatozoa and (4) X-SS fresh at 1×10⁶ spermatozoa. NS frozen controls of 20×10⁶ spermatozoa per straw were sourced from previously frozen ejaculates (n=3 bulls). Experiment 2: Aberdeen Angus ejaculates (n=4 bulls) were split across four treatments and processed as: (1) NS fresh 3×10⁶ spermatozoa, (2) Y-SS fresh at 1×10⁶ spermatozoa, (3) Y-SS fresh at 2×10⁶ spermatozoa and (4) X-SS fresh at 2×10⁶ spermatozoa. Controls were sourced as per Experiment 1. In vitro assessments for progressive linear motility, acrosomal status and oxidative stress were carried out on Days 1, 2 and 3 after sorting (Day 0=day of sorting. In both experiments SS fresh treatments had higher levels of agglutination in comparison to the NS fresh (P<0.001), NS frozen treatments had the greatest PLM (P<0.05) and NS spermatozoa exhibited higher levels of superoxide anion production compared with SS spermatozoa (P<0.05). Experiment 1 found both fresh and frozen SS treatments had higher levels of viable acrosome-intact spermatozoa compared with the NS frozen treatments (P<0.01).

In vitro sperm quality and DNA integrity of SexedULTRA™ sex-sorted sperm compared to non-sorted bovine sperm

SexedULTRA^™ is an improved method of sex-sorting sperm creating a less damaging environment to retain sperm integrity through the sorting process. The aim of this study was to evaluate the in vitro characteristics of fresh and frozen bovine sperm using the SexedULTRA^™ method, and compare it to conventional (non-sorted) sperm. For both methods, percent total sperm motility was estimated visually and also classified into total and progressively motile using a computer assisted sperm analyzer (CASA). Percent sperm with intact plasma membranes (VIA) and acrosomes (PIA) were assessed using flow cytometry and sperm DNA fragmentation index (DFI) was estimated using the Bull sperm Halomax^® Kit. Two contemporaneous ejaculates from 10 bulls were processed and cryopreserved using one of the two procedures (SexedULTRA^™ and conventional). Sperm motility, VIA and PIA were assessed post-thaw (0 h) and post-incubation (3 h at 37 °C, 8 h and 24 h at 18 °C). DFI was analyzed post-thaw (0 h) and after 6, 24, 48 and 72 h of incubation at 37 °C. In a second experiment, ejaculates from 7 bulls were split sampled into the two types of processing (SexedULTRA^™ and conventional) and diluted using a fresh semen extender developed for sex-sorted bovine sperm. Sperm quality was assessed after dilution (0 h) and after incubation for 12, 24, 48, 72 h at 18°, and the same time points of incubation at 37 °C for DFI. Frozen-thawed SexedULTRA^™ sperm was significantly (P < 0.05) better than conventional semen after a 3 h incubation at 37 °C for PIA, and after a 24 h incubation at 18 °C for percent visual motility and PIA. DFI was significantly lower for SexedULTRA^™ compared to conventional at all time points of incubation (37 °C). Fresh SexedULTRA^™ sperm showed improved quality compared to conventional at all time points of incubation at 18 °C for percent visual and total motile sperm, VIA, PIA, and DFI. Significant differences were also found in progressive motile sperm immediately after dilution (0 h), but not at any time point after incubation. The results show that the SexedULTRA^™ process maintains the quality of sex-sorted sperm and, in many cases, has better in vitro longevity than conventional semen.

Effects on glycocalyx structures of frozen-thawed bovine sperm induced by flow cytometry and artificial capacitation

Sperm sorting by flow cytometry is a useful technology in the bovine industry, but the conception rates after artificial insemination using sex-sorted sperm are lower than when using the un-sorted sperm. In this study, we have investigated the causes for these low conception rates. We have focused on changes caused by flow cytometry to the glycocalyx, which forms the outermost surface of the sperm membrane. We have also evaluated the effects of capacitation on the glycocalyx since capacitation involves a redistribution of the sperm membrane that is vital for successful fertilization and conception. Lectin histochemistry was used to visualize the structure of the sperm glycocalyx. Lectin-staining sites were examined in non-treated sperm, sex-sorted sperm, and capacitated sperm. We have detected six different staining patterns related to different labeling regions of the sperm. Phaseolus vulgaris–erythroagglutinin (PHA-E) lectin-staining patterns of non-treated sperm were very different from those observed for sex-sorted sperm or capacitated sperm, suggesting that both, sex sorting by flow cytometry and the capacitation process affected the glycocalyx structures in the sperm. In addition, the total tyrosine-phosphorylation level in sex-sorted sperm was significantly higher than that in the non-treated sperm. Therefore, we concluded that the unexpected capacitation of bovine sperm during flow cytometry is associated with changes in the glycocalyx. Since premature capacitation leads to low conception rates, this unexpected capacitation could be a cause of low conception rates after artificial insemination using sex-sorted sperm.

Effect of sex-sorting and cryopreservation on the post-thaw sperm quality of Iberian red deer spermatozoa

This study investigated the effect of sex-sorting and cryopreservation on post-thaw characteristics and fertility of red deer (Cervus elaphus) sperm for the first time. Semen was collected by electroejaculation from 10 mature stags during the breeding season, and each ejaculate split into four experimental groups: Bulk sorted spermatozoa, sorted but not sexed (BSS); sorted high purity X-spermatozoa (XSS); sorted high purity Y-spermatozoa (YSS); and, control non-sorted spermatozoa (NS). Following, all samples were frozen over liquid nitrogen. Two straws per stag and sample type were analyzed immediately post-thaw and following a 2-h incubation period at 37 °C. Post-thaw total motility (TM) as assessed by CASA was not different (P < 0.05) among NS, BSS and YSS sperm. For XSS, post-thaw TM was lower (39%, P < 0.05) than that for NS (54%) or BSS (50%), but similar (P > 0.05) to that of YSS (47%) sperm. The percentage of apoptotic spermatozoa as assessed by PI/YO-PRO-1 and flow cytometry analysis, was higher (17%, P ≤ 0.05) for XSS sperm than NS (12%), BSS (13%) and YSS (14%) sperm. Following incubation there were no differences (P > 0.05) in TM or percent apoptosis among treatments. Post-thaw chromatin stability calculated as the DNA fragmentation index (%DFI) was similar among treatments; following incubation %DFI increased in all except YSS, which displayed the lowest value (P < 0.05). Artificial insemination of synchronized hinds yielded 44, 52 and 62% delivery rates for YSS, NS and standard frozen-thawed sperm, respectively (P < 0.05). Notably, 93 and 55% of fawns born were males for the YSS and NS spermatozoa, respectively (P < 0.05). In summary, Y-sorted sperm displayed acceptable post-thaw sperm evaluation parameters and the expected offspring sex ratio. More studies are needed to understand the source of sperm damage that may compromise the fertility of Y-sorted red deer sperm.

Storage of sexed boar spermatozoa: Limits and perspectives

Despite the great potential application of sex-sorted spermatozoa in swine, the technology is not practiced in the pig industry because of technical factors and species-specific issues. The susceptibility of boar spermatozoa to stresses induced by the sorting procedure, the relative slowness of the sex-sorting process together with the high sperm numbers required for routine artificial insemination in pig are some of the main factors limiting the commercial application of this technology in pigs. This review briefly describes the damage to spermatozoa during sex sorting, focusing on an additional limiting factor: increased susceptibility of sexed boar spermatozoa to injuries induced by liquid storage and cryopreservation that, in turn, impairs sperm quality leading to unsatisfactory results in vivo. Strategies to extend the lifespan of sex-sorted boar spermatozoa and to improve their fertilizing ability after liquid storage or cryopreservation need to be implemented before this technology can be used in pig farms. In this regard, encapsulation in barium alginate membranes could be a promising technique to optimize the in vivo use of sexed boar spermatozoa, by protecting, targeting, and controlling the release of sperm into the female genital tract.

Sperm volumetric dynamics during in vitro capacitation process in bovine spermatozoa

Previous studies have demonstrated that sperm head morphometry can be used as a potential diagnostic tool for detecting biophysical changes associated with sperm viability in bovine spermatozoa. In this study, sperm head morphometry was used to investigate its value as a biophysical marker for detecting volumetric changes in bovine spermatozoa under in vitro capacitating and non-capacitating incubation conditions. To further test this hypotesis, aliquots of pooled, washed bovine sperm were incubated in either Tyrode's complete medium with heparin (TCMH; a capacitating medium containing Ca2+, NaHCO3 and heparin), Tyrode's complete medium heparin-free (TCM; a medium containing just Ca2+ and NaHCO3) or Tyrode's basal medium (TBM; a non-capacitating medium free of Ca2+, NaHCO3 and heparin, used as control). Aliquots of sperm were processed for morphometric analysis at different incubation-time intervals (0, 3 and 6 h at 38°C), and the chlortetracycline assay was used simultaneously to confirm the ability of the sperm to undergo capacitation (B pattern) and the acrosome reaction (AR pattern) status in each medium. After 3 h of incubation under TCMH conditions, a significant increase was observed in the percentage of B and AR patterns and a significant decrease was found in all sperm morphometric parameters (P<0.01). Interestingly, after 6 h of incubation in TCMH, the percentage of B and AR patterns increased drastically over time and marked differences were found in the dimensional and shape parameters, which were significantly smaller compared with TBM or TCM media (P<0.001). Significant correlations were observed between sperm size and AR pattern (r=-0.875, P<0.01). In conclusion, sperm head morphometry can be used as a potential biophysical marker for detecting volumetric changes during capacitation process in bovine spermatozoa.

Alkaline phosphatase in boar sperm function

Alkaline phosphatase (AP) catalyses the detachment of phosphate residues from different substrates. Its activity has been demonstrated in seminal plasma and spermatozoa from porcine and other mammalian species; anyway, the role of AP in male reproduction has not been clarified yet and the aim of this study was to determine AP function in boar sperm capacitation and in vitro fertilization (IVF). AP activity was assayed in seminal plasma and in uncapacitated and in vitro capacitated (IVC) spermatozoa; in addition, capacitation was studied in presence of different doses of AP (1.2 and 2.5 IU/mL). The effect of different doses of AP (1.2 and 2.5 IU/mL) on several sperm parameters after IVC (viability, acrosome integrity with FITC-PSA, capacitation status with CTC staining, tyrosine phosphorylation) and on fertilizing ability during IVF were also evaluated. High AP activity was detected in seminal plasma, in particular in sperm-rich fraction; a lower activity was detected in uncapacitated spermatozoa while a significant decrease was evidenced after IVC. Viability was not changed by AP supplementation of the capacitating medium, whereas acrosome integrity and capacitation status were significantly affected by 1.2 and 2.5 doses, with a dose-dependent decrease in acrosome-reacted cells as well as in CTC B pattern displaying cells. As for sperm head protein phosphorylation, a decrease in relative fluorescence was detected in AP 2.5 group, if compared with capacitated one. After IVF, a dose-dependent decrease in penetrated oocytes was recorded, with an increase in monospermic zygote rate. In conclusion, we demonstrated that AP activity decreases under capacitating condition and that addition of AP to spermatozoa during capacitation results in a depression of the capacitating process and IVF. We can infer that AP plays a role in keeping spermatozoa quiescent until they are ejaculated and in modulating the acquisition of the fertilizing ability.

Effect of sex sorting on stallion spermatozoa: Heterologous oocyte binding, tyrosine phosphorylation and acrosome reaction assay

The interest on sex sorting by flow cytometry on the equine industry has been increasing over the years. In this work, three different tests were performed in order to evaluate the membrane status of sorted stallion spermatozoa: assessment of binding ability to porcine oocytes, evaluation of acrosome integrity after stimulation with A23187, and detection of tyrosine phosphorylation. These evaluations were made after incubation for 0h, 1.5h and 3h in a capacitating medium. Sorted stallion spermatozoa attached similarly to the porcine oocytes, when compared with control samples. Sorted spermatozoa were more prone to undergo acrosome reaction (P<0.05), at the beginning and after 1.5h and 3h of incubation, and also had higher tyrosine phosphorylation of the tail (P<0.001), only at the beginning of the incubation period. Apparently sex sorted stallion spermatozoa are in a more advanced status of membrane destabilization, which could be associated with capacitation, although similar binding ability to porcine oocytes is maintained.