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

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.

Trends and challenges in liquid-preserved boar semen production: From boar to product

Boar semen production plays a pivotal role in modern swine breeding programmes, influencing the genetic progress and overall efficiency of the pork industry. This review explores the current challenges and emerging trends in liquid-preserved boar semen production, addressing key issues that impact the quality and quantity of boar semen. Advances in new reproductive technologies, boar selection, housing, semen processing, storage and transport, and the need for sustainable practices including the use of artificial intelligence are discussed to provide a comprehensive overview of the field.

Update of the cooling protocol for antibiotic-free storage of boar semen at 5°C improves sperm quality and maintains low bacterial counts

Preserving boar semen at 5°C instead of the conventional storage temperature of 17°C would enable a reduction of antibiotic use in pig insemination. To protect the chilling-sensitive boar spermatozoa, holding the extended semen at a higher temperature before cooling could be beneficial and facilitate the implementation of the innovative preservation concept in practice, provided that bacterial growth is kept at a low level. The aim of this study was to introduce a holding time (HT) at 17°C before cooling and to examine the effect on sperm quality and bacterial growth compared to the original cooling protocol for antibiotic-free 5°C semen storage. A series of experiments with semen doses from eight boars extended in Androstar® Premium without conventional antibiotics revealed that sperm kinematics and the integrity of sperm plasma membranes and acrosomes were improved with HT between 16 and 24 h followed by delayed cooling with 0.04°C/min when compared to the original protocol for semen preservation at 5°C (p < 0.05). Both a shorter HT of 6 h and a faster cooling rate of 0.07°C/min reduced sperm quality (p < 0.05). The HT for 24 h did not compromise the inhibitory effect on bacterial growth during long-term semen storage at 5°C, not even in semen doses spiked with Serratia marcescens. In conclusion, semen storage at 5°C with the modified cooling protocol improved sperm quality and is antimicrobially efficient. It thus presents a ready-to-use tool for a reduction or replacement of antibiotics in pig insemination.

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.

L-cysteine improves boar semen motility at 5 ºC but does not affect the oxidative status

Hypothermic storage has been proposed as a method to reduce bacterial loads and promoting prudent use of antibiotics. Reducing temperature, however, can lead to cold shock damage and oxidative stress in boar semen. This study verified the effect of L-cysteine on the quality of semen stored at 5 °C for 120 h. Twenty-one normospermic ejaculates were diluted in Beltsville Thawing Solution into five treatments: Positive control (Pos_Cont, storage at 17 °C without L-cysteine) and groups with 0, 0.5, 1, and 2 mmol/L of L-cysteine supplementation stored at 5 °C. Variables were analyzed as repeated measures, considering treatment, storage time, and interaction as main factors. The effects of different L-cysteine concentrations were also evaluated using polynomial orthogonal contrasts. Sperm motility and pH were higher in the Pos_Cont compared to the groups stored at 5 °C (P < 0.05). In polynomial orthogonal contrast models, total motility was affected by the interaction between L-cysteine and storage time (P = 0.04), with a linear increase in motility when increasing the amount of L-cysteine at 72 and 120 h. Progressive motility increased quadratically as the L-cysteine reached 1 mmol/L (P < 0.01). In the thermoresistance test at 120 h, sperm motility increased quadratically up to an L-cysteine dose of 1 mmol/L (P < 0.05). Sulfhydryl content linearly increased with L-cysteine supplementation (P = 0.01), with no effect on intracellular ROS and sperm lipid peroxidation (P ≥ 0.06) in 5ºC-stored doses. In conclusion, L-cysteine supplementation has a positive effect on sperm motility up to 120 h of storage at 5 °C.

Spermatozoa cooled to 5°C one day after collection from porcine commercial semen doses retain sperm functionality with reduced bacterial load

BACKGROUND

Commercial porcine semen is stored at 17°C, leading to a reduction of sperm quality and increase of bacterial growth.

OBJECTIVES

To evaluate the effect of 5°C storage on porcine sperm functionality cooled one day after collection.

MATERIALS AND METHODS

Semen doses (n = 40) were transported at 17°C and cooled at 5°C one day after collection. Spermatozoa were evaluated at Days 1, 4, and 7 for motility, viability, acrosome integrity, membrane stability, intracellular zinc, oxidative stress, and bacterial growth.

RESULTS

Contaminated semen doses predominantly exhibited Serratia marcescens, with increasing bacterial load during 17°C storage. Under hypothermal storage, negative doses for bacteria growth at Day 1 remained negative, and bacterial load did not increase in bacterial contaminated samples. Motility was significantly reduced through 17°C storage, but at 5°C, motility was only reduced at Day 4. Samples with bacterial growth (35.0%, 14/40) had significantly reduced motility at 17°C, but motility was unaltered at 5°C. Plasma membrane and acrosome integrity without bacterial contamination were unaffected at 17°C, but were significantly reduced at 5°C on Day 7. Plasma membrane and acrosome integrity significantly decreased with bacterial contamination regardless of temperature. High mitochondrial activity in viable spermatozoa without bacteria was not altered by temperature, but was significantly reduced by bacterial contamination at 17°C. Membrane stability was significantly reduced at Day 4, but tended (p = 0.07) to be higher in samples without bacterial growth. Viable spermatozoa exhibiting high zinc were significantly reduced throughout storage regardless of temperature. Oxidative stress levels were not altered, but significantly increased with bacterial contamination at 17°C.

DISCUSSION AND CONCLUSION

Porcine spermatozoa cooled to 5°C one day after collection retain functional attributes similar to spermatozoa stored at 17°C, but have a reduced bacterial load. Cooling extended boar semen to 5°C is feasible after transport to avoid modifying semen production.

The multidrug-resistant Pseudomonas fluorescens strain: a hidden threat in boar semen preservation

Although the bacterial composition of boar ejaculate has been extensively studied, the bacterial composition of extended boar semen is often overlooked, despite the potential risks these microorganisms may pose to the long-term preservation of extended boar semen at 15-17°C. In this study, we characterized the bacterial community composition of extended semen and discovered that Pseudomonas spp. was the dominant flora. The dominant strains were further isolated and identified as a potential new species in the Pseudomonas fluorescens group and named GXZC strain, which had adverse effects on sperm quality and was better adapted to growth at 17°C. Antimicrobial susceptibility testing showed that the GXZC strain was resistant to all commonly used veterinary antibiotics. Whole-genome sequencing (WGS) and genome annotation revealed the large genetic structure and function [7,253,751 base pairs and 6,790 coding sequences (CDSs)]. Comparative genomic analysis with the closest type strains showed that the GXZC strain predicted more diversity of intrinsic and acquired resistance genes to multi-antimicrobial agents. Taken together, our study highlights a problem associated with the long-term storage of extended boar semen caused by a P. fluorescens group strain with unique biological characteristics. It is essential to develop a new antibacterial solution for the long-term preservation of boar semen.

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.

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.

Update on artificial insemination: Semen, techniques, and sow fertility

Over the years, reproductive efficiency in the swine industry has focused on reducing the sperm cell number required per sow. Recent advances have included the identification of subfertile boars, new studies in extended semen quality control, new catheters and cannulas for intrauterine artificial insemination (AI), and fixed-time AI under commercial use. Therefore, it is essential to link field demands with scientific studies. In this review, we intend to discuss the current status of porcine AI, pointing out challenges and opportunities to improve reproductive efficiency.

Storage of Extended Boar Semen at 5 °C Inhibits Growth of Multi-Drug Resistant Serratia marcescens and Klebsiella oxytoca while Maintaining High Sperm Quality

Multi-drug antibiotic resistance of Serratia (S.) marcescens and Klebsiella (K.) oxytoca in boar semen is an emerging threat to pig reproduction and the environment. The aim of this study is to examine the efficiency of a novel hypothermic preservation method to inhibit the growth of these bacterial species in extended boar semen and to maintain the sperm quality. The semen samples extended in an antibiotic-free Androstar Premium extender were spiked with ~10² CFU/mL of S. marcescens or K.oxytoca. Storage at 5 °C for 144 h inhibited the growth of both bacterial species and maintained the sperm quality, whereas bacterial counts increased to more than 10¹⁰ CFU/mL in the 17 °C samples used as positive controls. This was accompanied by an increase in the sperm agglutination and the loss of motility and membrane integrity. We conclude that hypothermic storage is a promising tool to combat resistant bacteria in boar semen and to contribute to the One Health approach.

Bacteria and Boar Semen Storage: Progress and Challenges

Porcine breeding today is based on artificial insemination with chilled semen. This is stored at 5 °C with antibiotic supplementation to avoid bacteriospermia. There are many negative consequences on sperm quality and functionality as a result of bacterial contamination, as well as on the health of the sow. Nowadays, various techniques are being developed to reduce the indiscriminate use of antibiotics and thus avoid the generation of antibiotic resistance genes. This review aims to inform about the bacterial contamination consequences of storing liquid semen from boar and to provide an update on current methods and alternatives to antibiotic use in cold storage.

Cooled storage of semen from livestock animals (part I): boar, bull, and stallion

This review is part of the Festschrift in honor of Dr. Duane Garner and provides an overview of current techniques for cooled storage of semen from livestock animals. The first part describes the current state of the art of liquid semen preservation in boars, bulls, and stallions, including the diluents, use of additives, processing, temperature, and cooling of semen. The species-specific physiology and varying extents of cold shock sensitivity are taken into consideration. In addition, factors influencing the quality of cooled-stored semen are discussed. Methods, trends, and the most recent advances for improving sperm quality during cold-temperature storage are highlighted and their respective advantages and disadvantages are contrasted. There has been much progress in recent years regarding cold-temperature storage of boar sperm and there is great potential for a large-scale use to replace the current 17 °C temperature storage regime and the associated use of antibiotics in the future. For stallion sperm, there is an opposite trend away from previous low-temperature storage towards storage at higher temperatures to increase sperm viability and longevity. In bulls, liquid storage of sperm is mostly used in the seasonal dairy production systems of New Zealand and Ireland, but with further research focusing on shelf-live elongation of liquid preserved sperm, there is potential for an application in breeding programs worldwide.

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.

Microbiota in Goat Buck Ejaculates Differs Between Breeding and Non-breeding Seasons

Changes in semen microbiota are associated with alterations to sperm quality and fertility. However, the microbiota from most livestock species has not yet been studied. Goats are seasonal breeders, but semen microbiota has never been described in this species, and it is unknown how seasonality affects it. Our study objective is 2-fold: to describe the microbiota in goat buck ejaculates and to determine if it differs between breeding and non-breeding seasons. Semen from six males of the Murciano-Granadina breed was collected during both seasons. Two replicates were performed per male and season on different days. The microbiota was characterized by genomic sequencing technology. Sperm quality was also evaluated. Repetition was not significant for the studied variables. Sperm velocities were higher for the breeding than for the non-breeding season. The ejaculates from both seasons also differed in the proportion of apoptotic spermatozoa. The five dominant phyla were Firmicutes, Proteobacteria, Fusobacteria, Actinobacteria, and Bacteroidetes during the breeding season and Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria during the non-breeding season. The dominant genus during both seasons was Ureaplasma. Differences in microbial community structure (the beta diversity) were found. A decrease in the relative abundance of the genus Faecalibacterium and an increase in the genera Sphingomonas and Halomonas were observed in the ejaculates collected during the breeding season. Sphingomonas and Faecalibacterium abundance favorably and unfavorably correlated with sperm quality, respectively. In conclusion, the semen microbiota from goat bucks varies between breeding and non-breeding seasons, and the microbiota remains stable for 7 days within a season. In addition, the genera Sphingomonas and Faecalibacterium could be possible biomarkers of semen quality in goat bucks. These results contribute to an in-depth understanding of the effects of reproductive seasonality on goat buck ejaculates.

Assessment of Chilling Injury in Boar Spermatozoa by Kinematic Patterns and Competitive Sperm-Oviduct Binding In Vitro

Sensitive detection of chilling injury in boar spermatozoa is required to evaluate novel hypothermic preservation concepts. The study’s aim was to examine whether analyses of motility patterns and sperm binding in a competitive oviduct explant assay (cOEA) sensitively detect chilling-induced alterations in sperm function. Semen samples (n = seven boars) were split into four subsamples by dilution either in Beltsville Thawing Solution (BTS) or Androstar® Plus and stored at 5 °C or 17 °C. Storage temperature had a significant effect on the distribution of spermatozoa in seven major kinematic clusters. The effect size of chilling at 5 °C as estimated by Cramer’s V was higher (p < 0.05) in the BTS medium (0.21) compared to AndroStar® Plus (0.11). Spermatozoa extended in Androstar® Plus had higher relative binding capacity compared to sperm in BTS (p < 0.05). Binding indices correlated with the percentage of viable, acrosome-intact (r = 0.62) and motile spermatozoa (r = 0.72, both p < 0.001). The cluster size of sperm with slow, vigorous movement was negatively correlated with sperm-oviduct binding (r = −0.43, p < 0.05). In conclusion, the cluster analysis of sperm kinematics and competitive sperm oviduct binding in vitro present meaningful biological tests to assess novel concepts for hypothermic semen preservation.

Factors influencing the response of spermatozoa to agitation stress: Implications for transport of extended boar semen

The shipping of liquid preserved semen is common practice in animal breeding and prior to cryopreservation for gene banking. Vibration emissions during transport may be harmful to spermatozoa. Therefore, strategies to minimize agitation-induced sperm injury are needed. The aim was to examine whether the type of semen extender, time after semen processing and the temperature in simulated transport conditions influence the response of boar spermatozoa to agitation stress. In Experiment 1, boar semen samples (n = 16) extended in Beltsville Thawing Solution (BTS) or Androstar Plus (APL) medium were filled in 90 mL tubes and shaken for 4 h at 200 rpm either at 22 °C or 17 °C. Samples were then stored at 17 °C for 144 h. In Experiment 2, semen samples (n = 11) extended in Androstar Premium were shaken either directly after filling at 22 °C or 20 h later after cooling to 5 °C. Samples were stored at 5 °C for 144 h. In Experiment 1, sperm motility and viability were lower (p < 0.05) in the shaken samples compared to the controls. The temperature, extender and the storage length had no effect on the agitation-induced loss of sperm quality. Sperm quality traits were higher in samples stored in APL compared to BTS. In Experiment 2, sperm motility at 24 h was reduced (p < 0.05) in those samples shaken at 22 °C but not at 5 °C. Sperm viability, membrane fluidity and mitochondrial membrane potential were not affected in either of the treatment groups. Extended boar semen designed for 17 °C storage and shipped on the day of collection is sensitive to agitation stress. In contrast, spermatozoa slowly cooled to 5 °C and shaken 20 h after processing are more resistant to agitation-induced shear forces and interfacial phenomena.

In vitro performance and in vivo fertility of antibiotic-free preserved boar semen stored at 5 °C

BACKGROUND

Hypothermic preservation of boar semen is considered a potential method for omitting antibiotics from insemination doses, thereby contributing to the global antibiotic resistance defence strategy. The main challenges are chilling injury to spermatozoa and bacterial growth during semen storage leading to reduced fertility.

OBJECTIVES

To examine chilling injury and the number and type of bacteria in boar semen stored at 5 °C in the absence of antibiotics, and to assess the applicability of hypothermic semen storage under field conditions.

MATERIAL AND METHODS

Boar ejaculates were extended with AndroStar® Premium, stored at 17 °C with and at 5 °C without antibiotics and tested for functional sperm parameters by flow cytometry. Raw semen and extended samples were investigated bacteriologically. Fertility was evaluated after once-daily inseminations of 194 sows in a field study.

RESULTS

Lethal sperm damage assessed by motility and membrane integrity was low throughout storage in both experimental groups. Sublethal chilling effects based on the decrease of viable spermatozoa with low membrane fluidity were higher (P < 0.05) up until 72 h in sperm stored at 5 °C compared to 17 °C but did not differ after 144 h. After 72 h, incubation in capacitating medium for 60 min induced a similar decrease in viable sperm with high mitochondria membrane potential and low cytosolic calcium in both groups. In semen stored at 5 °C, bacteria counts were below 10³ CFU/mL and the bacteria spectrum was similar to that of raw semen. In 88% of 34 boars, cooled semen fulfilled the requirements for insemination. Fertility was high and did not differ (P > 0.05) between sow groups inseminated with semen stored antibiotic-free at 5 °C and semen stored at 17 °C with antibiotics.

CONCLUSION

Despite subtle chilling effects and low bacterial numbers, antibiotic-free hypothermic storage of boar semen offers the possibility to reduce the use of antibiotics in pig insemination. However, strict sanitary guidelines must be maintained and further evidence of efficiency under field conditions is considered desirable.

Assessment of chilling injury in hypothermic stored boar spermatozoa by multicolor flow cytometry

Hypothermic storage of boar semen may allow antibiotic-free semen preservation but is limited due to chilling sensitivity of boar spermatozoa. Progress in this area requires sensitive tools to detect chilling injury. Therefore, multiparameter flow cytometry panels were evaluated to ascertain whether they are useful tools for identifying sublethal damage of sperm function at a single cell level, thus considering the high intrinsic sperm heterogeneity in a sample. The first fluorochrome panel consisted of Hoechst 33342 to identify DNA-containing events, Yo-Pro 1 to detect viability, merocyanine 540 to describe membrane fluidity, and PNA-Alexa Fluor™ 647 to identify acrosomic integrity. The second fluorochrome panel consisted of SiR700-DNA to identify DNA-containing events, JC-1 to characterize the mitochondrial transmembrane potential (MMP), and Calbryte 630 to assess the intracellular calcium level. Extended boar semen was stored either at 17°C (control) or 5°C (chilled). It is shown that chilling increased membrane fluidity in the viable (Yo-Pro 1 negative) sperm population at 24 h (p < 0.05). At 144 h, the viable, acrosomic intact sperm population with low membrane fluidity was similar for both storage temperatures. Moreover, chilling reduced the main sperm population with high MMP, medium fluorescence for JC-1 monomer and low intracellular calcium level (p < 0.05). However, after in vitro sperm capacitation, this population did not differ between the two storage temperatures. Exemplary computational data visualization in t-distributed stochastic neighbor embedding (t-SNE) maps and moving radar plots revealed similar subpopulations as identified by three-dimensional stacked bar charts. In conclusion, sperm surviving an initial chilling injury withstand long-term storage and respond in a similar manner to capacitation conditions as sperm stored conventionally at 17°C. Multicolor flow cytometry is a valuable tool for detecting chilling-induced alterations of cell function in sperm subpopulations.

Relevance of Leptospira in boar and for the development of alternative antimicrobial concepts in boar semen preservation

Leptospirosis is a zoonotic disease of importance to public health and in livestock productions. It causes significant economic losses in pig breeding farms worldwide. However, actual transmission cycles and disease epidemiology in the pig population remain largely unknown. Despite the fact that the potential risk of venereal transmission of pathogenic Leptospira serovars in pigs has been a topic of discussion since the 1970s, reliable data are still lacking compared to other livestock species. Consequently, antibiotics are added to semen extenders to reduce bacterial contamination including pathogens like Leptospira. In view of the global threat of antimicrobial resistances, the routine use of antibiotics in porcine semen extenders is now under debate. Information about the prevalence of Leptospira infections in boar used for artificial insemination is needed for the development of novel antimicrobial concepts in pig insemination.

This short report provides a summary of the state of knowledge, together with negative results from real-time PCR analyses for the detection of pathogenic Leptospira DNA in boar semen. Molecular analyses were performed on 96 raw and extended samples obtained from normospermic ejaculates of 58 boar housed in six different studs in Germany. In the absence of reliable data, it is important to raise the awareness for a subject that can represent a challenge for pig productions in keeping reproductive health and food safety at high levels. The present molecular results indicate that Leptospira might not be a common threat in boar semen. Conclusive evidence would require results from a systematic serological surveillance of boar, combined with seasonal molecular analyses of semen to identify potential carriers, and assess actual seroprevalences, associated Leptospira serovars and transmission events.