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

Transport-related influences on the quality of liquid-preserved boar sperm: A review

This review explores the impact of transport-related stresses on the quality of liquid-preserved artificial insemination (AI) doses in pig reproduction. Transport of boar semen from AI centers to sow farms, the place of application, is an essential part of the production chain with increasing international demand, especially against the background of growing export demand. Understanding how factors such as: a) transport-related vibration emissions; b) temperature fluctuations during transport; c) transport duration; d) duration of storage after transport; and e) the method used for preserving AI doses, affect their quality is, therefore, essential for optimizing fertility outcomes. We provide a review of existing literature on the biological responses of liquid-preserved boar sperm to transport conditions. In addition, we discuss their impact on sperm quality and summarize potential mitigation strategies.

Contaminant toxicity of concern for boars and semen used in assisted reproduction programs

The commercial swine industry utilizes artificial insemination (AI) in their breeding programs. With this assisted reproductive technology, the process starts by obtaining fresh ejaculates from desirable boars who are housed in a dedicated facility (i.e., stud) that also contains a clean-room laboratory where semen quality is assessed and then ejaculates processed into AI doses. In concert with AI adoption, disruptions in sow herd reproductive performance have been traced back to contributions made from the boar stud. Through field investigations and research, several extrinsic contaminants have been identified that impact semen quality either at the boar or AI-dose level. These contaminants can be categorized as either biological or chemical in origin, eliciting reprotoxic outcomes at the boar level and/or spermatotoxicity at the AI-dose level. Biological contaminants include multiple genera of primarily opportunistic microbes (i.e., bacteria, fungi), along with their secondary metabolites (e.g., endotoxins, exotoxins, mycotoxins). Chemical contaminants appear to originate from products used at the stud, and include cleaning agent/disinfectant residues, leachates from gloves and plastics, semen extender impurities, purified and drinking water impurities, and pesticides (i.e., biocides, fungicides, herbicides, insecticides, wood preservatives). In conclusion, contaminants are a real and constant threat to the health and productivity of a stud, and have caused significant reproductive and economic losses in the swine industry. The knowledge gained in recognizing the types and sources of contaminants provides a solid foundation for the development and implementation of pro-active strategies that mitigate risk to the industry.

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.

Sperm quality and in vitro fertilizing ability of boar spermatozoa stored at 4 °C versus conventional storage for 1 week

Introduction

Since boar spermatozoa show a marked deterioration in sperm quality when cooled, insemination doses are usually stored at 16-18 °C. However, maintaining this temperature during transport of semen doses is challenging, particularly during the summer months. An alternative could be to store the doses at 4 °C if cold-shock to the sperm could be prevented. The objective of this study was to evaluate boar sperm quality and fertility in in vitro fertilization after storage in AndroStar Premium at 4 °C for 1 week.

Methods

Insemination doses (n = 9) in AndroStar Premium from a commercial boar semen collection station were transported to the laboratory at approximately 20 °C. At the laboratory, sperm quality evaluation and was preformed and each dose was split; half of each ejaculate was stored in a climate-controlled box at 16-18 °C, the other was slowly cooled to 4 °C. Both samples were stored for 1 week before further sperm quality evaluation and in vitro fertilization (IVF) were performed. Mean values were tested using generalized linear regression, with treatment and boar as fixed factors; p ≤ 0.05 was considered significant.

Results

Sperm membrane integrity (mean ± sem: 91 ± 0.05 and 83 ± 0.09% for 16 and 4 °C, respectively) and superoxide production (6.79 ± 2.37 and 13.54 ± 6.23% for 16 and 4 °C, respectively), were different between treatments. The DNA fragmentation index was lower in cold-stored samples than in conventionally stored samples (3.74 ± 2.25 and 7.40 ± 3.36% for 4 and 16 °C, respectively). The numbers of oocytes developing to blastocyst on Day 6 (mean ± sd: 9.0 ± 8.0 and 6.0 ± 5.0%, for storage at 16 and 4 °C, respectively) were not different between treatments.

Discussion

Therefore, storage of boar semen doses in AndroStar Premium at 4 °C for up to 7 days would be a viable alternative to current praxis.

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.

The Effect of Antimicrobial Peptide (PA-13) on Escherichia coli Carrying Antibiotic-Resistant Genes Isolated from Boar Semen

A major global public health concern is antimicrobial resistance (AMR). Antimicrobial peptides (AMPs) are a potentially appropriate replacement for conventional antibiotics. The purpose of this research was to investigate the potential of the antimicrobial peptide PA-13, a synthetic AMP with 13 amino acids, to inhibit E. coli isolated from boar semen expressing antibiotic-resistant genes, as well as to determine the mechanism of action of this antimicrobial peptide on the bacterial membrane. The effectiveness of the bacterial inhibitory activity of PA-13 was tested at different concentrations by two fold serial dilutions in the range 0.488-500 µg/mL using the MIC and MBC methods. The impact of PA-13 on the bacterial membrane was examined at different concentrations of 0×, 0.5×, 1×, 2× and 4× of MIC using DNA leakage assay and electron microscopy. The PA-13 antibacterial activity result exhibited the same MIC and MBC values at a concentration of 15.625 µg/mL. When comparing DNA leakage at different MIC values, the results revealed that the maximum amount of DNA concentration was found two and three hours after incubation. For the results of SEM and TEM, the bacterial membrane disruption of this E. coli was found in the PA-13-treated group when compared with the negative control. In conclusion, synthetic PA-13 with its antibacterial properties is an alternative antimicrobial peptide to antibiotics in the pig industry.

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.

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.

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.

One Health challenges for pig reproduction

The current state of the world challenges pig reproduction as an important part of One Health, which involves interrelationships between animal, human and environmental health. The One Health concept underlines a comparative aspect in reproductive physiology and disease occurrence, bridging knowledge from one species to another. Seasonal changes in the environment affect pig reproduction and climate change may further strengthen those effects. Endocrine-disrupting chemicals (EDCs), and specifically phthalates and heavy metals, interfere with endocrine function, and thereby sexual behavior, fertilization capacity and steroidogenesis. Reproductive infections and extended semen storage are important indications for antimicrobial use. Innovative solutions are needed to explore alternatives to antimicrobials. Efforts to ensure reproductive efficiency have prolonged farrowing as litter size has doubled over the past three decades, compromising immune transfer and welfare. Physiological, metabolic and programming related events around parturition are key areas for future One Health research in pig reproduction. In conclusion, climate change challenges reproductive management and breeding. More resilient pigs that can tolerate harsh environment but maintain high reproductive performance are needed. EDCs continue to grow as an environmental challenge for reproductive management and alternatives to antibiotics will be required.

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.

Antimicrobial activity of cell free supernatants from probiotics inhibits against pathogenic bacteria isolated from fresh boar semen

The use of antibiotics with semen extender appears to be a practical solution to minimise bacterial growth in fresh boar semen preservation. Unfortunately, the excessive use of antibiotics promotes antimicrobial resistance (AMR). This becomes a worldwide concern due to the antimicrobial resistance genes transmitted to animals, environment, and humans. Probiotics are one of the alternative methods to reduce antibiotic use. They could inhibit pathogenic bacteria by producing antimicrobial substances in cell free supernatants (CFS). Nevertheless, there is no comprehensive study undertaken on inhibitory activity against pathogenic bacteria isolated from boar semen origin. Our study investigated the efficacy of CFS produced from selected probiotics: Bacillus spp., Enterococcus spp., Weissella spp., Lactobacillus spp., and Pediococcus spp. inhibiting pathogenic bacteria isolated from fresh boar semen. Besides, the semen-origin pathogenic bacteria are subjected to identification, antimicrobial resistance genes detection, and antibiotic susceptibility test (AST). Pseudomonas aeruginosa, Escherichia coli, and Proteus mirabilis are the most common pathogens identified in boar semen with resistance to numerous antibiotics used in pig industry. The CFS with its antimicrobial peptides and/or bacteriocin constituent derived from selected probiotics could inhibit the growth of pathogenic bacteria carrying antimicrobial resistance genes (mcr-3 and int1 genes). The inhibition zones for Pseudomonas aeruginosa, Escherichia coli, and Proteus mirabilis provided more efficient results in the CFS derived from Lactobacillus spp. and Pediococcus spp. than those of the CFS produced from Enterococcus spp., Weissella spp. and Bacillus spp., respectively. It is worth noted that as the incubation time increased, the antibacterial activity decreased conversely. Our results on CFS with its antimicrobial peptides and/or bacteriocin constituent inhibits semen-origin pathogenic bacteria guide the direction as a promising alternative method used in the semen extender preservation of the pig industry.

Growth Dynamic and Threshold Values for Spermicidal Effects of Multidrug-Resistant Bacteria in Extended Boar Semen

The aim of this study was first to examine the prevalence of bacteria-associated loss of sperm quality in samples from insemination centers during a seven-year semen monitoring program and, second, to investigate the growth dynamic of four different multidrug-resistant bacterial species and their impact on sperm quality during semen storage. A reduced sperm quality associated with bacterial contamination was found in 0.5% of 3219 of the samples from insemination centers. In samples spiked with Serratia marcescens and Klebsiella oxytoca, bacterial growth by six log levels was seen during storage at 17 °C, causing loss of sperm motility, membrane integrity, membrane fluidity, and mitochondrial membrane potential at >107 CFU/mL (p < 0.05). Storage at 5 °C in the Androstar Premium extender efficiently inhibited their growth. Achromobacter xylosoxidans and Burkholderia cepacia showed limited growth up to two log levels at 17 °C and did not impair sperm quality. In conclusion, spermatozoa tolerate moderate loads of multidrug-resistant bacteria, and hypothermic, antibiotic-free semen storage effectively limits bacterial growth. The constant use of antibiotics in semen extenders should be reconsidered.

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.

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.

An Exploration of Current and Perspective Semen Analysis and Sperm Selection for Livestock Artificial Insemination

Artificial insemination of livestock has been a staple technology for producers worldwide for over sixty years. This reproductive technology has allowed for the rapid improvement of livestock genetics, most notably in dairy cattle and pigs. This field has experienced continuous improvements over the last six decades. Though much work has been carried out to improve the efficiency of AI, there are still many areas which continue to experience improvement, including semen analysis procedures, sperm selection techniques, sperm sexing technologies, and semen storage methods. Additionally, the use of AI continues to grow in beef cattle, horses, and small ruminants as the technology continues to become more efficient and yield higher pregnancy rates. In this review, AI trends in the various livestock species as well as cutting edge improvements in the aforementioned areas will be discussed at length. Future work will continue to refine the protocols which are used for AI and continue to increase pregnancy rates within all livestock species.

The Efficiency of Selected Extenders against Bacterial Contamination of Boar Semen in a Swine Breeding Facility in Western Slovakia

Simple Summary

This study evaluated the efficiency of selected semen extenders to prevent bacterial overgrowth in boar ejaculates stored for 72 h. Among the identified bacterial isolates, Escherichia coli and Pseudomonas aeruginosa were the most prevailing species. While all extenders supplemented with antibiotics ensured a satisfactory sperm vitality during the storage period, neither of them was able to achieve a complete elimination of bacteria from extended semen. Furthermore, a number of bacterial isolates exhibited resistance to several antibiotics chosen for the microbial susceptibility test (e.g., tigecyklin and ciprofloxacin).

Abstract

Bacteriospermia has become a serious factor affecting sperm quality in swine breeding, this is why antibiotics (ATBs) are a critical component of semen extenders. Due to ever-increasing antimicrobial resistance, the aim of this study was to assess the efficiency of selected commercially available semen extenders to prevent a possible bacterial contamination of boar ejaculates. Three Androstar Plus extenders containing different combinations of antibiotics were used to process ejaculates from 30 healthy Duroc breeding boars. Androstar Plus without antibiotics was used as a control. The extended samples were stored at 17 °C for 72 h. Sperm motility, viability, mitochondrial activity, DNA integrity and oxidative profile of each extended sample were assessed following 24 h, 48 h and 72 h. Furthermore, selective media were used to quantify the bacterial load and specific bacterial species were identified with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The results indicate that semen extenders enriched with ATBs ensured a significantly higher preservation of the sperm quality in comparison to the ATB-free control. The total bacterial count was significantly decreased in the extenders supplemented with ATBs (p < 0.001), however gentamycin alone was not effective enough against Gram-positive bacteria, while a few colonies of Enterococcus hirae, Bacillus subtilis and Corynebacterium spp. were present in the samples extended in the presence of a triple combination of ATBs. In conclusion, we may suggest that semen extenders enriched in antibiotics were not able to fully eliminate the bacteria present in the studied samples. Furthermore, selection of suitable antibiotics for semen extension should be accompanied by adequate hygiene standards during the collection and handling of boar ejaculates.

Antimicrobially Active Semen Extenders Allow the Reduction of Antibiotic Use in Pig Insemination

Antibiotic use in semen extenders for livestock may contribute to the development and spreading of multi-drug resistance. Antimicrobial control in semen doses for artificial insemination of pigs is indispensable due to the relatively high storage temperature (17 °C). The objectives of this study were first, to examine whether the antimicrobial capacity differs between antibiotic-free extenders and second, to determine whether an antimicrobial active extender provides the possibility to reduce antibiotics. Antibiotic-free semen extenders Beltsville Thawing Solution (BTS) and Androstar Premium were inoculated at 10³ to 10⁴ CFU/mL with four pure bacterial strains isolated from boar ejaculates or a mixture thereof, and then stored for 144 h at 17 °C. Bacterial counts after aerobic culture decreased in BTS up to one log level and decreased in Androstar Premium by 2 to 3.5 log levels (p < 0.05). In semen samples from nine boars stored in the inoculated Androstar Premium extender containing half of the standard concentration of gentamicin, bacteria counts were below 10¹ CFU/mL. Likewise, half of the standard dose of apramycin and ampicillin was fully antimicrobially active and sperm quality was maintained. In conclusion, semen extenders with intrinsic antimicrobial activity allow a reduction in antibiotic use in pig insemination.

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.

Antibacterial Activity of Some Molecules Added to Rabbit Semen Extender as Alternative to Antibiotics

Simple Summary

This study was conducted to evaluate the antibacterial activity of two aminopeptidase inhibitors and chitosan-based nanoparticles in liquid-stored rabbit semen. This study reports that the aminopeptidase inhibitors used to prevent bacterial growth could be used in semen extender as a suitable alternative to antibiotics.

Abstract

Although great attention is paid to hygiene during semen collection and processing, bacteria are commonly found in the semen of healthy fertile males of different species. As the storage of extended semen might facilitate bacterial growth, extenders are commonly supplemented with antibiotics. This study aimed to evaluate the antibacterial activity of ethylenediaminetetraacetic acid (EDTA), bestatin and chitosan-based nanoparticles added to rabbit semen extender and their effect on reproductive performance under field conditions. Four different extenders were tested, supplemented with antibiotics (TCG+AB), with EDTA and bestatin (EB), with EDTA, bestatin and chitosan-based nanoparticles (QEB) or without antibiotics (TCG-AB). Extended semen was cooled at 15 °C for three days. Cooled samples were examined for bacterial growth and semen quality every 24 h for 3 days. The enterobacteria count increased considerably during storage at 72 h in semen extended with TCG+AB and TCG-AB, while extenders EB and QEB showed a bacteriostatic effect over time. After 24, 48 and 72 h, quality characteristics were retained in all groups, with no significant motility differences, either in acrosome integrity, membrane functionality or the viability of spermatozoa. Additionally, bacterial concentration present in fresh semen did not affect reproductive performance. In conclusion, EDTA and bestatin exerted a potent bacteriostatic effect over time and could be used as an alternative to conventional antibiotics in rabbit semen extenders.