Temperature management during semen processing: Impact on boar sperm quality under laboratory and field conditions

Comparison between commercial media and TRIS-egg yolk extender in the refrigerated storage of collared peccary semen at 17°C

To assist in the conservation of collared peccary, it is important to strengthen semen processing protocols. The aim of this study was to compare the effects of different commercial extenders (BTS; NUTRIXcell+ and PRIMXcell Ultra) and TRIS + egg yolk on the functional and morphological aspects of collared peccary semen stored at 17 °C for 48 hours. Ten ejaculates obtained by electroejaculation were divided into 4 aliquots and diluted in the respective extenders, then stored in a biological incubator at 17 °C for 12, 24, 36, and 48 hours. The samples were evaluated for kinetic parameters, membrane functionality, membrane integrity, mitochondrial activity, morphology, and sperm-binding capacity. At the end of storage (48 h), promising results were found for motility parameters, with TRIS + egg yolk (71.0 ± 4.6%) being more efficient than NUTRIXcell+ (38.9 ± 10.9%) (P < 0.05) and similar to BTS (42.9 ± 11.9%) and PRIMXcell Ultra (46.8 ± 10.8%). The results for membrane integrity and mitochondrial activity were around ∼30-50%, with TRIS being the only extender to preserve both parameters (58.9 ± 5.3 and 59.2 ± 5.6%) for up to 48 hours, respectively (P < 0.05). Finally, the extenders could guarantee 60% membrane functionality and ∼ 60-70% normal sperm morphology, as well as similar binding capacity among the groups. In conclusion, TRIS + egg yolk is effective in preserving the sperm parameters of collared peccary semen at 17 °C for 48 hours, while PRIMXcell Ultra and BTS are viable alternatives for this purpose.

Boar semen storage at 5 °C for the reduction of antibiotic use in pig insemination: Pathways from science into practice

Storage of boar semen at 5 °C instead of the conventional temperature of 17 °C is an innovative preservation concept. It enhances protection against the growth of bacteria normally occurring in the ejaculates and potential drug-resistant contaminants from the environment. Thereby it allows the reduction or even elimination of antibiotics in porcine semen extenders. The present article reviews the current state of the low-temperature preservation approach of boar semen, with a special focus on antimicrobial efficiency and fertility in field insemination trials. Particularly the role of semen extenders and temperature management for the achievement of high fertility and biosecurity are elucidated. Insemination data of 1,841 sows in there different countries revealed equally high farrowing rates and litter sizes of semen stored at 5 °C compared to the controls stored at 17 °C. Microbiology data obtained from semen doses spiked with multi-drug resistant bacteria showed the efficiency of the cold semen storage for inhibiting the growth of Serratia marcescens, a bacterial species with high sperm-toxicity. Evolving concepts on the physiological role of the male reproductive microbiome for female fertility provides a further argument against the complete eradication of bacteria in the semen dose by antibiotic additives to the extenders. Finally, motivation and practical considerations for the use of the novel preservation tool in artificial insemination of pigs are revealed, which might encourage the transformation towards a sustainable production of boar semen doses following the One Health approach.

Vibration emissions affect the quality of liquid-preserved AI doses in stallions

Artificial insemination (AI) with liquid-preserved stallion semen is a widely used reproductive technology. As the demand for AI doses of high-class stallions is transnational, they are frequently exposed to long-distance transport. Since recent studies in boars indicated that vibration emissions caused by transport negatively affected sperm quality in vitro, this study questioned whether sperm quality in stallions is similarly impaired. Furthermore, we investigated stallion and extender-related differences in the spermatozoa's resistance to transport-related quality loss. Stallion ejaculates (n = 30) were collected at a German AI center, split in half, and subsequently diluted to a final sperm concentration of 50 × 106 sperm/mL using the semen extenders EquiPlus or Gent (both Minitüb GmbH, Germany). Four 12 mL aliquots of each sample were filled in plastic syringes according to a split-sample design and exposed to vibration (Displacement index Di = 3.0 ± 0.1) at 5 °C for 0 h (control), 3 h, 6 h or 9 h. All samples were stored for four days at 5 °C after transport simulation and analyzed for total sperm motility, thermo-resistance, membrane integrity, and mitochondrial activity determined by flow cytometry as well as the pH. After calculating generalized linear mixed models for each sperm quality trait, a negative impact of the duration of transport simulation could be shown on total sperm motility (P = 0.001), thermo-resistance (P = 0.030), and the pH (P = 0.001). Simulated transport for 6 h and 9 h diminished sperm quality (P ≤ 0.01), with 9 h reducing thermo-resistance by 5 ± 2.2% points (PP) for EquiPlus and sperm motility by 2.2 ± 1.7 PP for Gent compared to the control group. In contrast, samples exposed to vibration for 3 h showed no decline in sperm quality (P > 0.05). The individual stallion influenced every semen trait (P < 0.05) and transport-related losses in sperm thermo-resistance of up to 15.9 PP were demonstrated. Furthermore, EquiPlus was superior to Gent in all semen assessments (P < 0.001). We conclude that in vitro sperm quality is impaired by vibration. As the quality loss depends on the transport time, we recommend keeping shipping time as short as possible especially for spermatozoa of stallions that are susceptible to vibration-induced sperm quality loss.

Effects of vibrations during boar semen transport: Low-temperature transport as a new management tool

Transport-related vibrations (TV) compromise the quality of conventionally stored (17 °C) boar semen, but knowledge about TV effects after 5 °C transport is insufficient. This study evaluates the effects of TV after novel 5 °C transport compared to a 17 °C control. Ejaculates of 18 fertile Piétrain boars, diluted in a split sample procedure using Androstar Premium® (AP, 5 °C storage) or Beltsville Thawing Solution (BTS, 17 °C storage), were subjected to transport simulation using a laboratory shaker IKA MTS 4. The timing was set according to the respective processing protocols: for 17 °C BTS samples, TV simulation was performed the day of collection, 5 °C AP samples were subjected to TV the day after collection following completion of the established cooling curve to 5 °C. Six samples per ejaculate were exposed to different TV durations (0 h, 3 h, or 6 h) to evaluate the effect on sperm quality (progressive motility (PM), thermo-resistance test (30 and 300 min incubation at 38 °C (TRT30/TRT300)), mitochondrial activity (MITO), plasma membrane and acrosome integrity (PMAI)). Generalized linear mixed models revealed TV (P = 0.021) and storage time (P < 0.001) dependent declines in PM. Direct, pairwise comparisons revealed that 5 °C samples are not affected by TV (P(3 h vs. 6 h transport) = 1.0; P(0 h vs. 6 h transport) = 1.0). They therefore showed superior quality maintenance after TV compared to 17 °C samples (P(3 h vs. 6 h transport) = 0.025; P(0 h vs. 6 h transport) < 0.001). Concluding, low-temperature transport is possible without significant semen quality loss and with better quality maintenance than standard transport.

Effect of selenium nanoparticles on the quality and fertility of short-term preserved boar semen

This study was carried out to investigate the effect of different concentrations of selenium nanoparticles (Se-NPs) in the Beltsville Thawing Solution (BTS) extender on the semen quality and fertility of Hampshire crossbred pigs. For the study, semen was collected from four boars (10 ejaculates/boar) by the gloved hand method. Each ejaculate was extended @ 1:2 with the BTS extender and split into four aliquots. The control (C) samples were without the supplementation of Se-NPs, whereas the other three were supplemented with 0.5 (T1), 1 (T2), and 2 μg ml-1 of Se-NPs (T3) and stored at 15°C in a BOD incubator. Extended semen was evaluated at 0 (immediately after dilution), 24, 48, 72, and 96 h of storage for sperm motility, live sperm, plasma membrane integrity, acrosome integrity, DNA integrity, and mitochondrial membrane potential (MMP). The mean percentage of sperm motility, live sperm, and sperm with intact plasma membrane and acrosome, and MMPs were significantly (p < 0.01) higher in all treated groups in comparison to control at 24, 48, 72, and 96 h of storage. Sperm with intact DNA in all treated groups increased significantly at 48 (p < 0.05), and 72 and 96 (p < 0.01) h of storage in comparison to the control group. The concentration of 1 μg ml-1 of Se-NPs was found to be the best among other concentrations. In each group, 10 sows were artificially inseminated with the liquid semen preserved for 72 h at 15°C. Supplementation of 1 μg ml-1 of Se-NPs yielded the highest conception rate in comparison to other groups. In conclusion, supplementation of 1 μg ml-1 of Se-NPs in the BTS extender resulted in the best semen quality and conception rate during the short-time liquid preservation of boar semen.

Comparison of deep-litter bedding materials and analysis of semen traits in Piétrain boars: A randomized controlled field study

External factors can affect reproductive traits of breeding boars and especially the sensitive process of spermatogenesis. The aim of this study was to investigate probable influences of bedding materials (chipsy wood shavings (CWS), hemp straw (HS), linen straw (LS), spelt husks (SH), and regional wood shavings (RWS)) on semen traits of 40 randomly selected Piétrain boars (8 boars per group, age: 2.35 ± 1.23 years). After a six-week adaptation period, 40 fresh semen samples were collected weekly for four weeks and diluted in BTS (4 consecutive ejaculates per boar, 32 samples per group, 160 samples in total). Semen samples were analyzed using an extended range of spermatological methods (e.g., computer-assisted sperm analysis and flow cytometry). Generalized linear mixed models for each sperm parameter as well as the area under the curve for total sperm motility and thermo-resistance test were calculated. Materials LS and SH exceeded the standard maximum level for pesticide residues (VO (EG) No. 396/2005). Materials HS and LS presented the highest water-binding capacity of 413 % and 357 %, respectively, while SH showed the lowest value of 250 %. There were no significant (P > 0.05) differences between groups in any sperm characteristic, therefore indicating that bedding material had no influence on sperm quality. For most semen traits, however, we found significant (P ≤ 0.001) differences between sampling weeks. Based on pesticide results, we suggest CWS, RWS, or HS as possible bedding materials for pig production farms in the future. Furthermore, we strongly recommend a quality analysis of any new bedding material before use in swine husbandry.

Influence of age, breed, and season on the quality of boar semen stored at low-temperature

In the face of antimicrobial resistance, antibiotic-free, low-temperature storage of boar semen has been well-researched in recent years and promising results have been obtained. With the prospect of establishing this new preservation method in practice, it is important to evaluate a range of factors, possibly influencing the general and/or boar individual preservation suitability for 5 °C storage. The present study aimed to evaluate the influence of boar age (<18 months (n = 29) vs. 18-36 months (n = 68) vs. >36 months (n = 56)), breed (Pietrain (n = 104) vs. Duroc (n = 49)), as well as the influence of season (summer (n = 73) vs. winter (n = 80)) on the quality of boar semen preserved in antibiotic-free Androstar® Premium extender. AI doses were stored at 5 °C after cooling according to an established cooling protocol. In total, 153 ejaculates were analyzed throughout two identical experimental runs in summer and in winter, and the boars were divided into the corresponding sub-groups based on their age and breed. The application of a general linear model (GLM) and subsequent Bonferroni-corrected post hoc tests did not reveal any significant differences in the quality of semen stored at 5 °C between the different age groups. Regarding the season, a difference was found in the progressive motility (PM) at two out of seven analysis time points (P ≤ 0.01), however, this difference in PM was also present in fresh semen (P < 0.001). Most significant differences were found when comparing the two breeds. At six out of seven analysis time points, PM of Durocs was significantly lower than PM of Pietrains. Again, this difference in PM was also recognizable in fresh semen (P < 0.001). No differences were found in plasma membrane and acrosome integrity examined by flow cytometry. In conclusion, our study confirms the feasibility of 5 °C storage of boar semen under production conditions regardless of boar age. While season and breed have an influence on boar semen stored at 5 °C, these differences are not primarily caused by storage temperature, as they were already apparent in fresh semen.

Analysis of changes in the morphological structures of sperm during preservation of liquid boar semen in two different seasons of the year

Animal fertility is the result of a combination of genetic, physiological and environmental factors. Assessment of semen quality plays a key role in determining the reproductive performance of boars. The aim of the study was to determine the effect of two seasons of the year on the morphology, morphometry, cell membrane integrity and mitochondrial activity of sperm during storage of liquid boar semen at 17 °C. The study was carried out using 20 boars. Four ejaculates were collected from each boar in each of two seasons of the year. All tests were carried out five times: at 1, 24, 48, 96 and 168 h during storage. The results showed that sperm in ejaculates collected in summer are more sensitive to storage conditions than those from ejaculates obtained in winter. The percentage of sperm with morphological defects was shown to increase with the storage time of the diluted ejaculates, particularly between 96 and 168 h of preservation. In summer, the percentage of sperm with an intact cell membrane and the percentage with high mitochondrial membrane potential are much lower than in winter, at every hour of semen preservation. In the case of boars used for artificial insemination, it is worth taking into account the season when the semen is collected, especially if it is to be stored in liquid form. Assessment of sperm cell structures during storage of liquid semen should be implemented at insemination stations and should be carried out more often in summer.

Sperm concentration of boar semen doses and sperm quality: Novel perspectives based on the extender type and sperm resilience

This study evaluated the effect of sperm concentration of boar semen doses on their capacity to maintain its motility over the thermo-resistance test (TRT; sperm resilience) and verified if the extender type (short or long-term) could influence this effect. Thirty ejaculates from five crossbred mature PIC® boars were used, and a factorial design was followed to produce semen doses with 1.5 billion cells in 45 or 90 mL, using Beltsville Thawing Solution (BTS) or Androstar® Plus (APlus). Then, low-concentration doses (16.7 × 10⁶ cells/mL in 90 mL) and higher-concentration doses (33.3 × 10⁶ cells/mL in 45 mL) with BTS or APlus were produced and stored at 17 °C for 168 h. At 72 h, during the TRT, the low-concentration doses (16.7 × 10⁶ cells/mL) lost three-fold less motility than doses with 33.3 × 10⁶ cells/mL (P < 0.01), regardless of the extender type (11. 5% vs. 30.5% of initial motility, respectively). Similar results were found when the TRT was carried out at 168 h, with low-concentration doses losing two-fold less motility (11.4%) than highly concentrated doses (25.9%; P < 0.01). No sperm concentration effect was observed on membrane integrity or mitochondrial membrane potential (P ≥ 0.23). The osmolarity was not affected by the sperm concentration (P = 0.56), only by the extender and the storage time (P < 0.01). In conclusion, the sperm concentration effect on sperm quality was not influenced by extender type, and the data suggest that a low concentration of semen doses positively affects sperm resilience.

Science-based quality control in boar semen production

The ever-increasing understanding of sperm physiology, combined with innovative technical advances, continuously furthers the development of boar semen production management. These improvements pave the way for the future implementation of modified quality assurance concepts. This review provides an overview of current trends and new approaches in boar semen production, focusing on: the improvement of hygienic standards, alternatives to the use of antibiotics including the application of cold temperature storage and the utilization of antimicrobial additives, as well as the implementation of new quality control tools. Furthermore, the influence of dilution and temperature management, as well as new possibilities for an improvement of boar semen shipping and storage conditions are reviewed.

Intensity and Duration of Vibration Emissions during Shipping as Interacting Factors on the Quality of Boar Semen Extended in Beltsville Thawing Solution

Vibration emissions during the transport of boar semen for artificial insemination (AI) affect sperm quality. In the present study, the common influence of the following factors was investigated: vibrations (displacement index (D_i) = 0.5 to 6.0), duration of transport (0 to 12 h) and storage time (days 1 to 4). Normospermic ejaculates were collected from 39 fertile Pietrain boars (aged 18.6 ± 4.5 months) and diluted in a one-step procedure with an isothermic (32 °C) BTS (Minitüb) extender (n = 546 samples). Sperm concentration was adjusted to 22 × 10⁶ sperm·mL^-1. Extended semen (85 ± 1 mL) was filled into 95 mL QuickTip Flexitubes (Minitüb). For transport simulation on day 0, a laboratory shaker IKA MTS 4 was used. Total sperm motility (TSM) was evaluated on days 1 to 4. Thermo-resistance test (TRT), mitochondrial activity (MITO) and plasma membrane integrity (PMI) were assessed on day 4. Sperm quality dropped with increasing vibration intensity and transport duration, and the effect was enhanced by a longer storage time. A linear regression was performed using a mixed model, accounting for the boar as a random effect. The interaction between D_i and transport duration significantly (p < 0.001) explained data for TSM (-0.30 ± 0.03%), TRT (-0.39 ± 0.06%), MITO (-0.45 ± 0.06%) and PMI (-0.43 ± 0.05%). Additionally, TSM decreased by 0.66 ± 0.08% with each day of storage (p < 0.001). It can be concluded that boar semen extended in BTS should be transported carefully. If this is not possible or the semen doses are transported a long way, the storage time should be reduced to a minimum.

Bacterial killing activity and lysozymes: A stable defence mechanism in stallion seminal plasma?

During insemination, bacterial contamination of the ejaculate can lead to reduced sperm quality and transmission of pathogens to the female, thus should be avoided. The semen of a variety of animal taxa possess antimicrobial properties against a wide range of bacterial species through antimicrobial molecules, such as lysozyme, but their variance and the factors influencing it are unknown for most species. In this study, the antibacterial defence (bacterial killing activity (BKA) against Escherichia (E.) coli and Staphylococcus (S.) aureus as well as lysozyme concentration) was studied in seminal fluid from two consecutive ejaculates of 18 stallions. All ejaculates showed BKA against the tested bacteria, which correlated between the two consecutive ejaculates (r_S  = 0.526, p = .025 for E. coli and r_S  = 0.656, p = .003 for S. aureus) and appeared to be stable over the tested period. The lysozyme concentration (LC) showed no significant correlation between the consecutive ejaculates (r_S  = 0.161, p = .681). However, LC had a positive correlation to the ratio of apoptotic spermatozoa within the ejaculates (r_S  = 0.426, p = .019). In contrast to other livestock (e.g., boar, bull), the BKA in stallion semen did not correlate significantly with the age of the animal nor sperm quality characteristics.

In vitro aging of stallion spermatozoa during prolonged storage at 5°C

Artificial insemination with chilled stallion semen is hampered by a limited period of maximum fertility maintenance (24-48 h). This study used multiparametric flow cytometry to simultaneously measure reactive oxygen species (ROS) production, mitochondrial function or [Ca²⁺ ]_i and plasma membrane fluidity in viable, acrosome-intact spermatozoa, with the aim of providing insight into changes in sperm function during storage at 5°C. High proportions of viable and acrosome-intact spermatozoa (71 ± 8%) remained after 96 h of storage demonstrating that the basic integrity of the cells was well preserved (n = 17 stallions). In addition, more than 90% of viable, acrosome-intact spermatozoa had active mitochondria and low intra-cellular or mitochondrial ROS levels. By contrast, the percentage of viable, acrosome-intact sperm with low plasma membrane fluidity and low [Ca²⁺ ]_i decreased over time (1 h: 63 ± 16%, 96 h: 29 ± 18%; p < 0.05). The [Ca²⁺ ]_i in viable sperm rose 3.1-fold (p < 0.05) over the 4 days, and fewer spermatozoa responded to bicarbonate stimulation (1 h: 46 ± 17%, 96 h: 19 ± 12%) with an increase in plasma membrane fluidity following prolonged storage. Overall, prolonged storage of stallion semen at 5°C resulted in disturbed calcium homeostasis and increased plasma membrane fluidity. The decline in fertility of stallion semen during cooled-storage may therefore relate to aspects of in vitro aging (changes in plasma membrane fluidity and intracellular calcium) which impairs capacitation-associated cell functions.

A 5-color flow cytometry panel to assess plasma membrane integrity, acrosomal status, membrane lipid organization and mitochondrial activity of boar and stallion spermatozoa following liquid semen storage

For a more practically applicable analysis of different sperm characteristics, this study aimed to develop a 5-color flow cytometry (FC) panel to concurrently analyze four sperm parameters in liquid boar and stallion semen, using also a DNA-marker for selecting sperm cell events. From each of thirty extended boar semen doses and twelve stallion semen doses, six aliquots were taken. For evaluating mitochondrial activity (A), degree of lipid disorder of plasma membrane (B), integrity of plasma membrane (C), acrosomal status (D) and marking DNA (E), five aliquots were individually stained with Rhodamine 123, Merocyanine 540, Propidium Iodide, PNA-Alexa Fluor 647, and Hoechst 33342, respectively. The sixth aliquot was stained with all the five fluorochromes simultaneously, whereas spectral overlap was corrected by a compensation matrix. Strong correlations were found between the single and 5-color staining assays for boar sperm (A: 0.99, B: 0.96, C: 0.93, D: 0.98, E: 0.99; P < 0.01). Furthermore, moderate and substantial Concordance Correlation Coefficients (CCC) were presented by all these parameters (0.99, 0.96, 0.92, 0.98, and 0.99, respectively). For stallion sperm, the correlation coefficients between the assays were also strong (A: 0.99, B: 0.98, C: 0.99, D: 0.99, E: 0.95; P < 0.01) and substantial CCC were observed for all of them (0.99, 0.97, 0.99, 0.99, and 0.90, respectively). For both species, the mean difference between the methods (d̅) did not overtake 0.84. The results confirmed that this 5-color panel could be successfully implemented for analyzing boar and stallion sperm quality in a single, practical and quick FC assay.

Validation of a new multiparametric protocol to assess viability, acrosome integrity and mitochondrial activity in cooled and frozen thawed boar spermatozoa

BACKGROUND

Motility, morphology, membrane integrity and DNA fragmentation are sperm characteristics routinely used to assess quality of boar spermatozoa. However, the evaluation of individual parameters has intrinsic restrictions in the estimation of potential fertility. Therefore, we aimed to validate a new multiparametric protocol to assess fertility potential through the evaluation of viability, acrosome integrity and mitochondrial activity within the same sperm population for cooled and frozen-thawed boar spermatozoa.

METHOD

Three multicolor protocols to assess viability, acrosome integrity and/or mitochondrial activity were compared for agreement containing two dyes (HM-panel; Hoechst 33342, MitoTracker™ Deep Red), three dyes (3-panel; SYBR®14, propidium iodide and lectin PNA-Alexa™ 647) or four dyes (4-panel; Hoechst 33342, lectin PNA-Alexa™ 488, propidium iodide and MitoTracker™ Deep Red). Cooled (n = 132) and frozen-thawed (n = 254) samples of boar spermatozoa were assessed by flow cytometry.

RESULTS

4-Panel enabled the detection of several sperm subpopulations based on plasma membrane integrity, acrosome status and mitochondrial activity in cooled and frozen-thawed spermatozoa. No significant differences were observed between 3-panel and 4-panel for the percentage of live, live-acrosome intact, and dead-acrosome reacted spermatozoa. However, the percentage of acrosome-intact spermatozoa was significantly higher in cooled samples when stained by 3-panel than 4-panel. Percentages of sperm parameters between protocols were strongly correlated, and agreement analysis demonstrated that both assays resulted in similar values for both sperm sample type.

CONCLUSION

Our results indicate that a four-color protocol is a practical, simple and reliable procedure to simultaneously evaluate boar sperm viability, acrosome integrity and mitochondrial activity under clinical conditions.

Temperature limits for storage of extended boar semen from the perspective of the sperm's energy status

The optimum storage temperature for liquid-preserved boar semen has been empirically determined to be between 15 and 20°C. Lower temperatures provide an advantage to inhibit bacterial growth, but are regarded as critical due to the high sensitivity of boar spermatozoa to chilling injury. Higher storage temperatures are supposed to induce energy deficiency due to an insufficient depression of metabolic cell activity. However, experimental evidence for alterations of the sperm's energy status in relation to storage temperature and duration is missing. Therefore, we aimed to revisit the upper and lower storage temperature limits for liquid-preserved boar semen from the perspective of the sperm's energy metabolism. Ejaculates (n = 7 boars) were cooled down in Beltsville Thawing Solution (BTS) to 25, 17, 10, or 5°C and stored for up to 120 h. ATP and adenylate energy charge (EC) levels were assessed at storage temperature (24, 72, and 120 h storage) and after subsequent re-warming (38°C). Sperm quality and energy status remained at a stable level in samples stored at 25 and 17°C. Chilling to and storage at 10 or 5°C in BTS provoked cold shock in a subset of sperm as shown by a loss in viability and motility (P < 0.05), which was accompanied by a significant release of adenine nucleotides into the semen extender. Prolonged storage for 120 h resulted in significantly lower mean ATP concentrations in viable spermatozoa at 5 or 10°C compared to 17°C (P < 0.05). Cluster analysis revealed that the main sperm subpopulation, i.e., sperm with moderate speed and linearity, decreased from 50 to 30% (P < 0.05) in favor of slow-moving spermatozoa (5°C) or spermatozoa with a hyperactivation-like motility pattern (10°C). The results point to a sublethal imbalance in available ATP in a subset of the surviving sperm population, rather than a general decrease in available ATP in all spermatozoa. In conclusion, storing diluted boar semen at a stable temperature between 17 and 25°C is a safe procedure concerning the spermatozoa's energy status. Future concepts for hypothermic boar semen preservation below 17°C require measures which ameliorate the imbalanced energy status in viable spermatozoa.

Boar Semen Shipping for Artificial Insemination: Current Status and Analysis of Transport Conditions with a Major Focus on Vibration Emissions

In the modern pig reproduction system, artificial insemination (AI) doses are delivered from AI centers to sow farms via logistics vehicles. In this study, six breeding companies in three countries (Brazil, Germany, and the USA) were interviewed about their delivery process. It was found that there is currently no comprehensive monitoring system for the delivery of semen. The entire process “shipping of boar semen” was documented using Business Process Model and Notation (BPMN). Although it is not currently known which vibrations occur at all, it is suspected that vibration emissions affect the quality of boar semen. For this reason, a prototype of a measuring system was developed to calculate a displacement index (Di), representing vibration intensities. Vibrations were analyzed in standardized road trials (n = 120) on several road types (A: smooth asphalt pavement, B: rough asphalt pavement, C: cobblestone, and D: dirt road) with different speeds (30, 60, 90, 120, and 150 km/h). A two-way ANOVA showed significant differences in mean Di, depending on road surface and speed as well as an interaction of both factors (p < 0.001). A field study on a reference delivery from a German AI center to several sow farms indicated that 33% of the observed roads are in good quality and generate only a few vibrations (Di ≤ 1), while 40% are of a moderate quality with interrupted surfaces (Di = 1−1.5). However, 25% of the roads show markedly increased vibrations (Di ≥ 1.5), as a consequence of bad conditions on cobblestones or unpaved roads. Overall, more attention should be paid to factors affecting sperm quality during transport. In the future, an Internet of Things (IoT) based solution could enable complete monitoring of the entire transport process in real time, which could influence the courier’s driving behavior based on road conditions in order to maintain the quality of the transported AI doses.

Should All Fractions of the Boar Ejaculate Be Prepared for Insemination Rather Than Using the Sperm Rich Only?

Simple Summary

The swine industry is constantly looking for efficiency improvement, especially focusing on the artificial insemination (AI) process. One of the trends in AI centers is to maximize the number of doses obtained from one ejaculate. Seminal doses are usually prepared with the sperm-rich fraction or the whole ejaculate, but further studies are needed to understand how to prepare them properly. Thus, this study aims to analyze how accumulative ejaculate fractions may influence sperm storage, AI performance, and offspring. The results indicate that the presence of all ejaculate fractions within seminal doses does not affect either sperm quality or AI performance and offspring health. Therefore, this study highlights the possibility to use the bulk ejaculate for seminal dose preparation, leading to successful AI. Additionally, it results in a more time-efficient preparation of a greater number of seminal doses providing an economic advantage.

Abstract

Boar ejaculate is released in several well-characterized fractions, differing in terms of sperm concentration, seminal plasma volume, and composition. However, the inclusion of the last part of the ejaculate for artificial insemination (AI) purposes is still under debate due to its controversial effects. Thus, there is a need to study the potential synergistic impact of the different ejaculate fractions. We aimed to evaluate the effect of accumulative ejaculate fractions on sperm conservation, AI performance, and offspring health. Ejaculates (n = 51) were collected and distributed as follows: F1: sperm-rich fraction; F2: sperm-rich + intermediate fractions; F3: sperm-rich + intermediate + poor fractions. Each group was diluted in a commercial extender, packaged in seminal doses (2000 × 10⁶ sperm/60 mL), and stored at ~16 °C. On day 3 of conservation, sperm were analyzed and used for AI (n = 174). High sperm quality was observed after storage without a significant difference between the groups (p > 0.05). Moreover, no differences were obtained for AI performance (pregnancy and farrowing rates, and litter size; p > 0.05) and offspring health (growth and blood analysis; p > 0.05). Conclusively, the presence of all ejaculate fractions within the seminal doses does not impair the reproductive performance, reporting important economic savings according to the economic model included here.

Relevance of the Ejaculate Fraction and Dilution Method on Boar Sperm Quality during Processing and Conservation of Seminal Doses

During boar semen processing and distribution, maximizing the work protocols in the laboratories becomes essential for the conservation of seminal doses. One of the recent implementations in the boar studs to improve efficiency has been semi-automatic semen collection systems, which do not allow to discard fractions of the ejaculate. The objective of this work was to evaluate the dilution method and vibrations (simulating delivery transport) effect on sperm quality (motility, viability, morphology, thermo-resistance test) according to the fraction of ejaculate collected. Two different fractions of the ejaculate were obtained [rich fraction (RF); total fractions (TF)] from six boars, and two dilution methods applied [pouring the extender over the semen (control; ES); pouring the semen over the extender (reverse; SE)]. The seminal doses (2000 × 10⁶ sperm/50 mL) were preserved for 5 days. The results showed that the fraction collected affects sperm quality (better total and progressive motility, and faster sperm in TF; p < 0.05) regardless of the dilution method applied. However, these differences diminished after submitting the semen to the thermo-resistance test, with only differences in sperm viability being observed (p < 0.05). When seminal doses were subjected to vibrations, the sperm viability was more affected in the TF than in the RF group (p < 0.05). In conclusion, using the TF ejaculate leads to comparable results to the RF in sperm quality during storage regardless of the dilution method applied. However, the vibrations of seminal doses are more affected in doses prepared with TF than with RF, although more factors should be included to approach the real conditions during transport.

Integrity of Sperm Cell Membrane in the Semen of Crossbred and Purebred Boars during Storage at 17 °C: Heterosis Effects

Simple Summary

The cell membrane of spermatozoa is the main structural element of these gametes. In boars, due to its structure, it is most susceptible to various types of damage induced by various factors. Artificial insemination in pigs mainly involves the use of liquid semen preserved at 17 °C. Thus, it is important to monitor this semen during its storage. In practice, the changes that can take place in sperm during the preservation and storage of boar semen are not analysed. Furthermore, considerable variation is observed in the characteristics of boar semen, which may depend on the breed or crossbreeding variant of the boar. Crossbred boars are often used in artificial insemination, because they not only easily produce ejaculates with good parameters, but also have good libido characteristics. However, despite the benefits of artificial insemination with semen of crossbred boars, there is insufficient knowledge of the sensitivity of cell structures to conditions associated with semen storage in comparison with boars of the parent breeds. For this reason, a study was conducted to analyse changes in the integrity of sperm cell membranes taking place during the storage of semen collected from Duroc × Pietrain crossbred boars and purebred boars of the parent breeds. The sperm of Duroc × Pietrain crossbred boars were found to be less sensitive to the conditions of semen storage and to better retain cell membrane integrity than the sperm of purebred males, which was confirmed by calculating the heterosis effects for semen assessed at different hours of storage at 17 °C.

Abstract

The aim of the study was to assess changes in the integrity of sperm cell membranes during the storage of semen collected from Duroc × Pietrain crossbred boars and purebred boars of the component breeds. To compare the cell membrane integrity of sperm heads in crossbred and purebred boars, heterosis effects were estimated. The study was conducted on 48 ejaculates collected from Duroc × Pietrain crossbred boars and from purebred Duroc and Pietrain boars used for artificial insemination. Microscope slides were prepared from each ejaculate for the evaluation of the cell membrane integrity of the sperm, at 1, 24, 48, 72, and 96 h after collection of the ejaculate. Diluted ejaculates were stored at 17 °C. Sperm membrane integrity was analysed by two methods: SYBR-14/PI and eosin–nigrosin. Our results showed that the cell membrane integrity of sperm heads changed with storage time, but the extent of the changes varied depending on the genetic group of boars. The semen of Duroc × Pietrain crossbreds was clearly seen to be less sensitive to storage conditions than that of boars of the parent breeds, which was confirmed by the calculated heterosis effects. The percentage of sperm with an intact cell membrane was higher in crossbred boars than in purebred boars (p ≤ 0.05). In addition, significantly fewer moribund sperm spermatozoa and spermatozoa with a damaged cell membrane were observed in crossbred boars (p ≤ 0.05). In the semen of purebred Duroc and Pietrain boars, the cell membrane integrity of the sperm should be assessed more often during storage than in the semen of Duroc × Pietrain crossbred boars. This study provides valuable information for the development and implementation of semen quality monitoring in crossbred boars and boars of the parent breeds during storage at 17 °C with respect to the cell membrane structure of sperm heads. The evaluation methods used effectively identify damage to the cell membranes of the sperm during semen storage.

Suitability of semen stress tests for predicting fertilizing capacity of boar ejaculates

Besides classical semen parameters, semen stress tests (SSTs) are helpful tools to assess the fertilizing capacity of sperm. However, valid studies on SSTs in relation to fertility are rare because several corrections of common fertility parameters for female and male effects are required. Therefore, over a one-year period, we analyzed semen parameters of 260 ejaculates obtained from 130 Pietrain boars aged between 8 and 9 months in one AI center as well as 1521 corresponding insemination records for these ejaculates. Two consecutive ejaculates (4th and 5th) were collected from each boar and extended in DiluPorc™ BTS. In addition to routine semen evaluation, sperm motility was assessed after heat-resistance test (300 min incubation at 38 °C after seven days storage at 16 °C, HRT) and cold-resistance test (10 min incubation at 38 °C after three days storage at 6 °C, CRT). Generalized linear models (GLMs) were applied to analyze effects for the following predictors of farrowing rate (FR), number of total born (NTB) and live born (NLB) piglets: farm (P = 0.013 [FR], P = 0.001 [NTB], P = 0.023 [NLB]), parity (P = 0.679, P = 0.01, P < 0.001), weekday (P = 0.012, P = 0.08, P = 0.009) and year × season (P < 0.001, P = 0.688, P = 0.574). On boar level, GLMs revealed significant effects on FR, NTB and NLB for the predictors sow (all P < 0.001), total sperm number per dose (P = 0.007, P = 0.002, P < 0.001), total sperm motility (P = 0.002, P = 0.2, P = 0.003) and mitochondrial activity (P = 0.004, P < 0.001, P = 0.002). Moreover, FR and NTB were influenced by membrane integrity (both P < 0.001), FR and NLB by cold-resistance (P < 0.001, P = 0.043), and NTB and NLB by sperm morphology (P = 0.001, P < 0.001) and boar (both P < 0.001). NLB was additionally influenced by heat-resistance (P = 0.004) and farm (P = 0.018) and solely NTB was influenced by sperm output (P = 0.03). Boar and semen related factors explained 9% of the total variation in NTB and 7% of the total variation in NLB. Only 14.2% (n = 37) of the samples were both cold- and heat-resistant (≥65% of motile sperm). Cold- and heat-resistance were dependent factors (Chi-square, P = 0.001) and sperm motility after CRT and HRT showed a moderate positive correlation (r_s = 0.40, P < 0.001, Spearman's rho). Finally, ROC curves demonstrated that neither SST can be used as a sole test for predicting the fertilizing capacity of boar ejaculates.

Development of a new antimicrobial concept for boar semen preservation based on bacteriocins

The conventional storage temperature of 16-18 °C provides optimal conditions for the preservation of boar sperm quality, which are extremely cold sensitive cells. On the other hand, however, it requires the addition of antibiotics to inhibit bacterial growth. Rising numbers of antibiotic resistant bacteria call for alternatives to this conventional storing method. As potential alternative, three different bacteriocin candidates with known bacteriolytic activity against E. coli were examined on possible negative effects concerning the sperm quality and on their impact on bacterial growth of E. coli ILSH 02692 in BTS-extended semen w/o antibiotics. Although the lower concentrations (0.01 and 0.25%) of all bacteriocins did not show any impact on the quality of the semen, the higher concentrations (0.5 and 1.0%) of two bacteriocins led to a significant (P < 0.05) reduction in several sperm quality characteristics. The bacteriocin 860/1c after AMS/dialysis did not affect the sperm quality in any of the tested concentrations and in all tested extenders (BTS, MIII, Androstar Premium and Androhep all w/o antibiotics) at 16 °C as well as at 6 °C. This bacteriocin reduced growth of E. coli ILSH 02692 in BTS-extended semen by 50% compared to the control w/o bacteriocin. Furthermore, a preliminary insemination trial indicated no impact of the selected bacteriocin on fertility. These promising results show that the application of bacteriocins in liquid-preserved semen is a feasible possibility in the future.

Effects of bone morphogenetic protein 15 (BMP15) knockdown on porcine testis morphology and spermatogenesis

Bone morphogenetic protein 15 (BMP15) is a member of the transforming growth factor-β (TGFB) superfamily that plays an essential role in mammalian ovary development, oocyte maturation and litter size. However, little is known regarding the expression pattern and biological function of BMP15 in male gonads. In this study we established, for the first time, a transgenic pig model with BMP15 constitutively knocked down by short hairpin (sh) RNA. The transgenic boars were fertile, but sperm viability was decreased. Further analysis of the TGFB/SMAD pathway and markers of reproductive capacity, namely androgen receptor and protamine 2, failed to identify any differentially expressed genes. These results indicate that, in the pig, the biological function of BMP15 in the development of male gonads is not as crucial as in ovary development. However, the role of BMP15 in sperm viability requires further investigation. This study provides new insights into the role of BMP15 in male pig reproduction.

Effect of sperm concentration on boar spermatozoa mitochondrial membrane potential and motility in semen stored at 17 °C

The aim of the study was to assess the effect of sperm concentration in the ejaculate on the mitochondrial membrane potential and motility of Landrace boar spermatozoa during storage of diluted semen at 17 °C. The study was conducted on ejaculates collected from 10 boars aged 1.5–2 years. Based on sperm concentration measurements, two groups of boars were identified: Group 1 – boars providing ejaculates with a sperm concentration of at least 500 × 103/mm3 and Group 2 – boars providing ejaculates with a sperm concentration of less than 500 × 103/mm3. Four ejaculates were collected manually from each boar. Each ejaculate was diluted with Biosolvens Plus diluent, and insemination doses were prepared and stored at 17 °C. Mitochondrial membrane potential and motility of spermatozoa were evaluated at each insemination dose. The tests were carried out after 1, 24, 48, 96 and 168 h of storage. Based on the results, it was found that ejaculates with a sperm concentration ≥ 500 × 103/mm3 have a lower share of spermatozoa with high mitochondrial membrane potential than ejaculates with a sperm concentration below 500 × 103/mm3. A high correlation between the share of spermatozoa with a high mitochondrial membrane potential and motility of spermatozoa was demonstrated in the first 24 h and after 96 h of semen storage, which was confirmed by the calculated phenotypic correlation coefficients. Sperm cells in ejaculates with a higher sperm concentration are more sensitive to storage time than spermatozoa in ejaculates with a lower concentration.

Evaluation of a panel of spermatological methods for assessing reprotoxic compounds in multilayer semen plastic bags

The increase of fertility performance in sows is one of the biggest achievements in pig production over the last 30 years. Nevertheless, pig farms using artificial insemination (AI) repeatedly experienced in recent year’s fertility problems with dramatic consequences due to toxic compounds from plastic semen bags. In particular, bisphenol A diglycidyl-ether (BADGE) present in multilayer plastic bags can leach into the semen and could affect the functionality of the spermatozoa. Former studies could not find any alterations in spermatozoa based on the exposure to BADGE. The aim of the study was to evaluate effects of BADGE on boar spermatozoa using an extended panel of spermatological methods. In spring 2019, a large drop in farrowing rates from 92.6 ± 2.3% to 63.7 ± 11.1% in four sow farms in Croatia was detected. In migration studies, BADGE could be identified as a causal toxic compound and leached into the extended semen in concentration of 0.37 ± 0.05 mg/L. Detailed spermatological studies showed that significant predictors for effects on spermatozoa were different levels of motility and kinematic data after a prolonged storage time, thermo-resistance test (prolonged incubation time), mitochondrial activity, membrane integrity and fluidity. No serious effects were observed for sperm morphology and DNA fragmentation. These results provide new insights into the development of a new quality assurance concept for a detailed spermatological examination during testing of plastic materials for boar semen preservation. It could be shown that boar spermatozoa are an excellent biosensor to detect potential toxicity and fertility-relevant compounds.

Comparative analysis of various step-dilution techniques on the quality of frozen Limousin bull semen

Background and Aim:

Indonesia has two National Artificial Insemination centers and 17 Regional Artificial Insemination Centers. The frozen semen production techniques differed between the centers, including the type of diluent and semen dilution technique. The aim of the research was to compare the quality of frozen Limousin bull semen diluted using different techniques.

Materials and Methods:

Semen was collected from three sexually mature Limousin bulls using an artificial vagina. Immediately after collection, the semen was evaluated macroscopically and microscopically. Semen that had >70% motile sperm and <20% sperm abnormality was divided into three tubes and diluted with skim milk-egg yolk (SMEY) using three different dilution techniques: One-step dilution (100% SMEY with 8% glycerol) at room temperature ([RT] 20°C until 25°C) two-step dilution (50% SMEY without glycerol at RT, stored at 5°C; and 50% SMEY with 16% glycerol after 1 h stored at 5°C); and three-step dilution (50% SMEY without glycerol at RT, stored at 5°C; and 50% SMEY with 16% glycerol added twice at 1 h and 1.5 h after being stored at 5°C). The diluted semen was loaded into 0.25 mL mini straws, equilibrated, and frozen using a freezing machine. Sperm motility, viability, membranes, DNA integrity, and concentrations of malondialdehyde (MDA) and aspartate aminotransferase (AST) enzymes were evaluated after thawing.

Results:

The results showed that there were no significant differences in sperm motility and DNA integrity between dilutions (p>0.05). However, sperm viability and membrane intactness of one-step dilutions were higher than those of three-step dilutions. The concentrations of MDA and AST enzymes of sperm in one-step dilutions were lower than those of three-step dilutions (p<0.05).

Conclusion:

It was concluded that the one-step-dilution technique was better than three-step dilution for cryopreservation of Limousin bull semen.

Fluorescent labelling of boar spermatozoa for quantitative studies on competitive sperm-oviduct binding

Invitro sperm-oviduct binding assays enable assessment of the capacity of spermatozoa to form a 'reservoir' in the oviduct. Competitive approaches, such as experimental set-ups that test multiple males or semen samples simultaneously on the same tissue explants, are desirable because they reduce the likelihood of bias when using material from different females. Therefore, we established a fluorescent labelling technique that allows tagging and storage of spermatozoa before competitive studies of sperm-oviduct binding invitro. Fluorescent markers were tested for reliability and compatibility with parameters of boar spermatozoa viability. The addition of seminal plasma after density gradient centrifugation was essential to counteract centrifugation stress during the labelling procedure. It was demonstrated that sperm tagged with MitoTracker Green FM or MitoTracker Red FM can be successfully used in competitive sperm-oviduct binding studies. The assay was sensitive enough to indicate subtle effects of semen storage temperature on the ability of the spermatozoa to contribute to the female sperm reservoir.

Low temperature preservation of porcine semen: influence of short antimicrobial lipopeptides on sperm quality and bacterial load

Antimicrobial resistance is a steadily increasing problem and poses a serious threat to global public health. Therefore, it is highly necessary to advance the development of novel antimicrobial compounds and semen preservation strategies. The aim of this study was to evaluate a low temperature, antibiotic-free preservation procedure using Androstar Premium (ASP) extender (Minitüb) with antimicrobial lipopeptides. Firstly, seven lipopeptides in two concentrations (1 × minimum inhibitory concentration (MIC)/2 × MIC) were tested on their sperm-compatibility at 17 °C. Two lipopeptides, C16-KKK-NH₂ and C16-KKKK-NH₂, did not negatively affect sperm quality and were further evaluated for their efficiency of bacterial growth inhibition at 5 °C. Besides an overall diminution of colony forming units, both peptides showed a reduction of bacterial subcultures (n = 103) with a decrement in Gram-positive rods from 65 (ASP w/o supplements) to 39/52 (ASP w/ C16-KKK-NH₂/C16-KKKK-NH₂), in Gram-positive cocci from 21 to 9/10 and in Gram-negative species from 17 to 8/5 total subcultures. Furthermore, lipopeptides revealed activity towards selected bacteria of potential concern in artificial insemination like Trueperella pyogenes, Alcaligenes faecalis, Pseudomonas aeruginosa (not C16-KKK-NH₂), Pasteurella sp., Providencia stuartii, Escherichia coli (not C16-KKKK-NH₂) and Streptococcus porcinus (not C16-KKKK-NH₂). Consequently, both tested lipopeptides are promising candidates for alternative antibiotic-free preservation techniques of boar semen.

Insemination of sows with seminal doses prepared by a two-step hypothermic dilution does not impair the reproductive performance at farm

Reproduction in swine is mostly carried out through artificial insemination (AI). For this purpose, AI studs collect the ejaculates, analyse the sperm quality, dilute and package to produce seminal doses and ship them to sow farms to carry out the AI. Temperature is controlled during the process to avoid sperm damage. Semen is diluted in the extender in a one-step or a two-step process where the second can be isothermic (approximately 32°C) or hypothermic (room temperature 21-22°C). Both techniques are currently performed, and the latter could reduce time and costs, but the literature available comparing the processes is scarce and presents discrepancies. To date, there are no studies about its impact in fertility. This study compared hypothermic two-step dilution (HTSD) and isothermic two-step dilution (ITSD) in laboratory and field trial to elucidate whether HTSD has any effect. Ejaculates from 72 boars in nine AI studs were split and processed with both techniques using a high-performance extender and evaluated in laboratory. Four farms inseminated 345 sows with samples of four of these AI studs, and their fertility and prolificacy were registered. Results show no significant differences between doses prepared by HTSD and ITSD technique, having no impact in laboratory results (percentage of motile sperm, short hypoosmotic swelling test (sHOST) and short osmotic resistance test (sORT), viable sperm, damaged acrosomes, sperm under early apoptosis, high mitochondrial membrane potential (p > .1), fertility (92.2% versus 94.1%, p = .45) or farrowing rate (15.8 ± 0.3 versus 16.1 ± 0.3 p = .46). In conclusion, our results suggest that HTSD of semen on extender could be safely implemented in AI studs under the conditions tested.

Determination of a cooling-rate frame for antibiotic-free preservation of boar semen at 5°C

Hypothermic storage of boar semen provides the possibility to omit antibiotics from semen extenders so long as sperm quality is maintained and bacterial growth prevented. The objective of this study was to determine an optimal cooling-rate frame for boar semen preserved at 5°C in an antibiotic-free extender. Semen from eight boars extended in AndroStar^® Premium was cooled from 30°C to 5°C using seven different cooling rates, ranging initially from 0.01 to 0.36°C min^–1 and reaching 5°C between 2 h and 24 h after dilution. Sperm motility, membrane integrity, membrane fluidity, mitochondrial membrane potential and the response to the capacitation stimulus bicarbonate remained at a high level for 144 h at 5°C when the semen was initially cooled in a cooling-rate frame ranging from 0.01 to 0.09°C min^‑1 in the temperature zone from 30 to 25°C, followed by 0.02 to 0.06°C min^–1 to 10°C and 0.01 to 0.02°C min^‑1 to the final storage temperature. A cooling rate of 0.07°C min^–1 in the temperature zone from 30 to 10°C led to a reduced response to bicarbonate (P < 0.01) and fast cooling to 5°C within 1 h with a cooling rate of 0.31°C min^–1 resulted in lower values (P > 0.05) of all sperm parameters. In a further experiment, slow cooling with a holding time of 6 h at 22°C induced after 6 h storage a temporary increase in Escherichia coli of 0.5 × 10³ to 2.4 × 10³ CFU mL^–1 in the sperm-free inoculated extender. Overall, the load of mesophilic bacteria in the stored semen was below 6 × 10³ CFU mL^–1, a level that is not regarded as critical for sperm quality. In conclusion, appropriate cooling protocols were established for the antibiotic-free storage of boar semen at 5°C, allowing the application of hypothermic preservation in research and in artificial insemination.

Antibiotic-free extended boar semen preserved under low temperature maintains acceptable in-vitro sperm quality and reduces bacterial load

This study aimed to assess the sperm quality and number of colony-forming units (CFU mL^-1) in extended boar semen stored at low temperatures with or without antibiotics. Normospermic ejaculates (n = 34) were diluted in split samples with Androstar® Premium with or without antibiotics (ampicillin and apramycin sulfate). The extended semen doses were stored for 120 h under three storage temperatures (5, 10, and 17 °C). Variables were analyzed as repeated measures using the GLIMMIX procedure, in a factorial design. The extended semen doses under low-temperature storage (5 and 10 °C) had total motility above 75% throughout the storage. The interaction antibiotic × temperature was significant for total (P = 0.004) and progressive motility (P = 0.005). In extended boar semen doses with antibiotics, the total and progressive motility increased as the storage temperature increased (80.2%, 84.5%, and 89.1%; 70.5%, 76.0%, and 82.9% for total and progressive motility at 5, 10, and 17 °C, respectively; P < 0.05). In extended semen doses without antibiotics, the total and progressive motility were lower when stored at 5 °C than at 10 °C and 17 °C (81.8%, 85.4% and 86.6% and 71.9%, 76.7%, 78.9% for total and progressive motility at 5, 10, and 17 °C, respectively; P < 0.05). After the thermoresistance test, total and progressive motility of doses with antibiotics were higher at 17 °C than 5 °C (P < 0.05); however, they were not affected (P > 0.05) by storage temperature in extended semen doses without antibiotics. The number of CFU mL^-1 was lower in extended semen doses without antibiotics stored at 5 and 10 °C than at 17 °C (P < 0.05); however, in extended semen doses with antibiotics, no effect of storage temperature was observed (P > 0.05). The bacterial load was greater in extended semen without antibiotics than with antibiotics, regardless of the storage temperature (P < 0.05). The acrosome and sperm membrane integrity were not influenced (P > 0.05) by using antibiotics. A higher percentage of normal acrosomes was observed as the storage temperature increased (93.6%, 94.3%, and 96.8% at 5, 10, and 17 °C, respectively; P < 0.0001). The membrane integrity was higher (P < 0.0001) in extended semen doses stored at 17 °C than at 10 or 5 °C. The pH rose throughout the storage in all the treatments, except in extended semen doses stored at 17 °C without antibiotics, in which a decrease in the pH occurred at 120 h (P < 0.05). Although the sperm quality being negatively affected by low temperatures, the storage of extended boar semen doses at 5 °C is possible since the sperm viability in vitro was maintained for up to 5 days, fulfilling the requirements of semen quality to be used in artificial insemination. Nevertheless, the use of extended semen doses without antibiotics requires the optimization of hygiene procedures during semen dose processing.

Effect of boar seminal dose type (cervical compared with post-cervical insemination) on cooling curve, sperm quality and storage time

Seminal doses used for cervical and post-cervical artificial insemination (CAI and PCAI, respectively) vary in volume, the number of spermatozoa and packaging. The aim was to evaluate the outcomes when there was use of routine processing procedures for CAI- and PCAI-doses. Two different types of seminal doses were processed: 1) CAI: 2.7 × 10⁹ sperm/80 ml; 2) PCAI: 1.5 × 10⁹ sperm/45 ml. In Experiment 1, the cooling curve of seminal doses during processing occurred in two phases: 1st) At room temperature (23.4 ± 0.5 °C) from 0 (just after packaging) to 120 min; 2nd) At refrigeration (15.7 ± 0.8 °C) from 121-240 min. For the PCAI-doses, the time required to reach room temperature was 47 min compared to 107 min for CAI-doses (decreasing velocity of 0.093 °C/min and 0.048 °C/min, respectively). During refrigeration, for the PCAI-doses the time required to reach the desired preservation temperature was 20 min less than for CAI-doses (PCAI: 90 min, 0.074 °C/min; CAI: 110 min, 0.066 °C/min). In Experiment 2, sperm motility, kinetic parameters and acrosome damage for both types of doses were evaluated at 0, 24, 48 and 72 h of refrigeration. Also, morphology, pH, and osmolality were assessed at 0 and 72 h. Values for all these did not differ between CAI- and PCAI-doses. In conclusion, PCAI-doses took less time than CAI-doses to reach the desired temperature, but sperm quality was similar for CAI- and PCAI-doses during storage. Nevertheless, the different cooling curves should be taken into consideration for further investigation.

An update on boar semen assessments by flow cytometry and CASA

In the quest for predicting fertility of an individual, enhancing semen handling, dilution and storage protocols, and understanding the impact of environment and, andrologists have changed their approaches to semen analysis. The technologies used today are fast developing and readily implemented in research. Semen is one of a few naturally occurring monocellular suspensions, so sperm function analysis by flow cytometry (FC) and utilization of fluorochromes is an ideal technique for high throughput, objective and accurate analysis. The complementary use of microscopical assessments by Computer-Assisted Semen Analysis (CASA), where sperm cell parameters can be objectively assessed is equally important. The objectivity and repeatability of these techniques have driven research on the function, identification of heterogeneity and fertility of the ejaculate. The wealth of knowledge obtained from the application of these powerful methods has changed our view of the spermatozoon. Although there is some application of these methods in the industry producing boar semen for artificial insemination (AI) and to eliminate sires of sub-standard semen quality, uptake of advanced methods is still slow. Instruments are becoming cheaper and technically more user friendly. Standardization of methodology and optimization of instrument settings is important for full implementation of these systems, including comparison between labs. This review provides an update on two technologies: flow cytometry and CASA for objective analysis of boar semen quality.

Application of preserved boar semen for artificial insemination: Past, present and future challenges

Artificial insemination (AI) is now used for breeding more than 90% of the sows in most of the world's primary pork producing countries. Despite the advancement of methods to cryopreserve boar semen, frozen semen has not been routinely used on farms because of limited efficiency. Liquid semen on the other hand, with 1.5-3 billion sperm per dose preserved up to seven days in long-term extenders, is in common use and is largely responsible for the widespread use of AI. Breeding organizations have defined individual thresholds for useable semen at 60-80% for motility and bacterial load of 0-1000 CFU/mL. Improvement in preservation techniques for liquid semen and better education of producers has been responsible for the higher efficiency of pig breeding, as measured by conception rate and increased litter size, with a minimum number of sperm. The introduction of deep intrauterine AI and advances in breeding management have also been contributing factors. The present article reviews the worldwide application of preserved boar semen from past to present and delineates future challenges. Pathways to increase breeding efficiency are outlined. The reconciliation of AI with sustainable breeding strategies is increasingly important. In this sense, guidelines for the prudent use of antibiotics in semen extenders are proposed. More efficient and sustainable pig AI awaits the introduction of sex-sorted sperm into AI practice. Another critical milestone that needs to be achieved is the replacement of conventional antibiotics in extenders.

New trends in production management in European pig AI centers

Reducing the number of spermatozoa per artificial insemination (AI) dose and managing semen in ways to ensure greater quality at the same time represents current challenges with sperm processing in pig AI centers. Based on a multi-year comparative analysis of process steps in different pig AI centers, and complementary experimental studies under standardized laboratory conditions, current process standards for the preservation of boar semen have been updated and new ones developed. Currently, these standards represent an integral part of the quality assurance of 29 European pig AI centers in ten different organizations in Germany, Switzerland and Austria. Improvement of hygiene management and guidelines for prudent use of antibiotics have become key issues. Furthermore, new quality control tools have been implemented in the processing and transport of boar semen: e.g. refractometry as an easy-to-use tool to estimate extender osmolarity and 'mobile sensing' apps for continuous monitoring of various environmental parameters. Moreover, based on a series of experiments under laboratory and field conditions, guidelines for optimizing the dilution process, and time and temperature management during boar semen processing, have been developed and implemented. Similarly, recommendations for the handling of semen doses during storage have been renewed. Over the years, the efficiency of the quality assurance system has been reflected by a decrease of bacterial contamination and a concomitant increase in the quality of semen doses. In conclusion, science-based quality assurance is an effective way to improve the production performance in pig AI centers, resulting in high quality and economically-priced semen for pig producers. Increasing knowledge of sperm physiology together with computational and technical innovations will continue to develop and modify quality assurance concepts in the future.

Effect of dietary grape marc on fresh and refrigerated boar semen

In several studies there has been evaluation of the dietary addition of antioxidants to improve the quality of fresh and stored semen in domestic animals. Grape marc (GM), as the residue of vinification, contains large amounts of polyphenols with antioxidant, anti-inflammatory, antimicrobial, and antiaging effects. In this study, two regimens of dietary GM supplementation (2% and 4%) were tested regarding effects on the characteristics and lipid peroxidation of fresh and stored semen. The dietary supplementation of GM improved sperm characteristics in fresh semen, especially at 4% of GM. There were greater values for all kinetic variables and membrane integrity, and lesser values for sperm abnormalities and lipid peroxidation with 2% and 4% GM supplementation. Lipid peroxidation of the pellet was less with both 2% and 4% GM supplementation. During sperm storage, the dietary supplementation of GM improved the quality of sperm, with greater values for kinetic variables and membrane integrity at day 15 of storage. In the present study, supplementation of GM in boar diets improved fresh semen characteristics and reduced the lipid peroxidation of ejaculated spermatozoa, possibly due to the effect of polyphenols present in the GM. Consequently, this likely resulted in improved sperm quality during storage.

Detection and characterization of Lactobacillus spp. in the porcine seminal plasma and their influence on boar semen quality

The presence of pathogenic bacteria in ejaculates has been a topic in boar semen preservation over the last decades. Since little information is available on commensal bacteria in boar semen, the aim of the present study was to identify commensal lactobacilli in fresh cryopreserved boar semen and to examine their influence on boar semen quality. Therefore, 111 boar ejaculates were investigated for the presence of Lactobacillus species. Thirty samples (27%) contained viable Lactobacillus species (e.g. L. amylovorus, L. animalis, L. reuteri and Weisella minor). L. animalis and L. buchneri DSM 32407 (isolated from the bovine uterus) qualified for further examinations based on their growth rate in six antibiotic-free boar semen extenders. After a 120 min short-term incubation with an antibiotic-free BTS-extender, progressive motility was diminished (P = 0.001) upon addition of 105 and 106 colony forming units (CFU/mL) L. animalis. The supplementation with L. buchneri DSM 32407 had no significant (P > 0.05) influence on sperm quality during short-term co-incubation. After 168 h long-term co-incubation, motility analysis revealed a negative (P = 0.026) impact of 105 CFU/mL L. buchneri DSM 32407. A concentration- and storage-dependent effect is particularly obvious (P < 0.001) using 106 CFU/mL L. buchneri DSM 32407. Most notably, the thermo-resistance (TRT) for 106 CFU/mL L. buchneri DSM 32407 (P = 0.001) was inferior to BTS with and without gentamicin after 72 and 168 h of semen co-incubation. The supplementation of 105 CFU/mL L. buchneri DSM 32407 impaired progressive motility to a lesser extent. The percentage of mitochondrially active spermatozoa after 96 h (P = 0.009) and membrane-intact spermatozoa after 168 h (P < 0.001) was lower when 106 CFU/mL L. buchneri DSM 32407 were suspended compared with all other groups. Finally, the addition of L. buchneri DSM 32407 to BTS-extended boar semen had no competitive effect on the total amount of bacteria 48 h after co-incubation. In summary, the present study demonstrated that there are Lactobacillus species present in the porcine seminal plasma, which can be cultivated using standard procedures. However, long-term co-incubation of lactic acid bacteria with spermatozoa had a negative influence on spermatozoa.

Irradiation of semen doses with LED-based red light in a photo chamber does not improve in vitro quality of thermically stressed boar spermatozoa

Recent reports indicate that stimulation of liquid-stored boar semen with red LED-based light improves sperm quality and reproductive performance in sow herds. So far, in vitro data after LED stimulation of whole semen doses are lacking. In this study, the effect of LED light exposure on the in vitro quality of boar spermatozoa after storage and thermic incubation was examined. Boar semen doses were stored at 17°C (n = 10) or 5°C (n = 6) in Beltsville Thawing Solution extender and then exposed to red LED light using a commercial photo chamber. During a subsequent long-term incubation at 38°C, neither sperm kinematic parameters nor mitochondria function or membrane integrity differed between control and treated samples (p > .05). It is concluded that stimulation of semen doses in the LED-photo chamber does not improve quality of thermically stressed boar sperm in vitro. Other than the sperm traits tested here might be involved in the previously reported improvement of in vivo fertility.

Effect of production management on semen quality during long-term storage in different European boar studs

The processing of ejaculates is a fundamental step for the fertilizing capacity of boar spermatozoa. The aim of the present study was to identify factors that affect quality of boar semen doses. The production process during 1 day of semen processing in 26 European boar studs was monitored. In each boar stud, nine to 19 randomly selected ejaculates from 372 Pietrain boars were analyzed for sperm motility, acrosome and plasma membrane integrity, mitochondrial activity and thermo-resistance (TRT). Each ejaculate was monitored for production time and temperature for each step in semen processing using the special programmed software SEQU (version 1.7, Minitüb, Tiefenbach, Germany). The dilution of ejaculates with a short-term extender was completed in one step in 10 AI centers (n = 135 ejaculates), in two steps in 11 AI centers (n = 158 ejaculates) and in three steps in five AI centers (n = 79 ejaculates). Results indicated there was a greater semen quality with one-step isothermal dilution compared with the multi-step dilution of AI semen doses (total motility TRT d7: 71.1 ± 19.2%, 64.6 ± 20.0%, 47.1 ± 27.1%; one-step compared with two-step compared with the three-step dilution; P < .05). There was a marked advantage when using the one-step isothermal dilution regarding time management, preservation suitability, stability and stress resistance. One-step dilution caused significant lower holding times of raw ejaculates and reduced the possible risk of making mistakes due to a lower number of processing steps. These results lead to refined recommendations for boar semen processing.

Boar management and semen handling factors affect the quality of boar extended semen

Artificial insemination (AI) is the preferred method for reproduction in the majority of the intensive pig production systems Worldwide. To this end, fresh extended ready-to-use semen doses are either purchased from AI-centres or produced by boars kept on-farm. For profitable semen production, it is necessary to obtain a maximum amount of high quality semen from each boar. This paper reviews current knowledge on factors that may affect semen quality by influencing the boar or the semen during processing. Genetic markers could be used for early detection of boars with the highest fertility potential. Genetic selection for fast growth might jeopardize semen quality. Early detection of boars no longer fit for semen production might be possible by ultrasonography of the testes. Seasonal variation in sperm quality could be associated with changes in photoperiod and heat stress during summer. Comfortable housing, with appropiate bedding material to avoid locomotion problems is essential. In some areas, cooling systems may be necessary to avoid heat stress. The sperm quality can be manipulated by feeding strategies aiming, for instance, to increase sperm resistance to oxidative stress and extend storage duration. High collection frequency will negatively influence sperm quality. Also, if collection is not hygienically performed it will result in bacterial contamination of the semen doses. The concern over bacterial contamination has risen not only because of its negative effect on semen quality but also due to the detection of antimicrobial resistance in isolates from extended semen. Moreover, bacterial and viral pathogens must be monitored because they affect semen production and quality and constitute a risk of herd infection. During processing, boar sperm are submitted to many stress factors that can cause oxidative stress and capacitation-like changes potentially reducing their fertility potential. Dilution rate or dilution temperature affects the quality of the semen doses. Some packaging might preserve semen better than others and some plastic components might be toxic for sperm. Standard operation procedures and quality assurance systems in AI centres are needed.

Impact of different dilution techniques on boar sperm quality and sperm distribution of the extended ejaculate

The dilution of ejaculates is a fundamental step for the production of liquid-preserved boar semen. For a long time, it has been recommended to add the extender to the ejaculate. The aim of the present study was to first compare the effect of the position ('center' vs. 'wall') where the extender is added to the semen-mixing cylinder (height 32.5cm; diameter 12.7cm) using an automatic dispenser (n=11). In experiment 2 (n=30), we analyzed the two main dilution methods (extender to the semen ('control') vs. 'reverse'). Experiment 3 was carried out to study the dilution effect on kinematics. In Experiments 1 and 2, the sperm distribution 10min after the dilution and the sperm quality parameters during long-term storage (d1, d3, d5, and d7) were evaluated. In Experiment 3, sperm quality was assessed during short-term storage at 0, 10, 20, 30 and 60min after semen dilution ('control' vs. 'reverse'; n=6). There were no significant differences (P>0.05) between the treatments in the specific response to bicarbonate, mitochondrial activity, membrane status, thermo-resistance or sperm motility immediately after dilution or long-term storage. The sperm distribution was significantly (P=0.029) affected by the dilution method in Experiment 2. In summary, treatment with the extender first, which is used by only a few European boar studs, leads to comparable results in sperm quality during storage and better results in sperm distribution after dilution. This procedure is also less time consuming, less foam formation occurs during the semen dilution and the procedure is more hygienic.

Quality Control of Boar Sperm Processing: Implications from European AI Centres and Two Spermatology Reference Laboratories

In recent years, increased automatization has resulted in a higher efficiency of boar semen processing in AI laboratories. Sophisticated laboratory management and efficient quality control programmes are needed for current tendencies in major pork-producing countries to reduce the sperm number per AI dose, to lengthen semen storage times and to adopt responsible methods for bacterial control and prevention of the development of multiresistant bacteria. The objective of the present review was to outline current trends in boar semen production and the critical steps in semen processing which affect sperm quality. In addition, integrated elements of a quality assurance programme in use by thirty European AI centres in association with the two German spermatology reference laboratories are described.