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

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.

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.

Validation of the volumetric flow cytometry for bovine sperm concentration

Sperm concentration is a stronghold of the andrological evaluation and the production of insemination doses. The use of haemocytometers, although considered the gold standard, is difficult to apply in field conditions because it is subjective and time-consuming. The present study was designed to validate the volumetric flow cytometry (volFC) in order to estimate bovine sperm concentration, comparing it with the performances of haemocytometer, NucleoCounter, and flow cytometry with the use of fluorospheres. Compared with other methods, volFC appeared less affected by large dilution of the sample, with similar concentrations calculated in the range of dilution 1:200-1:800. Using volFc the population detected on the basis of morphological criteria and fluorescence of DNA better represents the real concentration of sperm in the sample. The volFC showed high repeatability compared with the haemocytometer (coefficient of variation 1.85% and 4.52%, respectively) and stable performances with cryopreserved samples, with negligible effects of the medium components. The present study showed that volFC is as accurate and precise as other techniques to estimate sperm concentration in bovine fresh and frozen semen, but it is less affected by operative conditions, such as sample dilution. The possibility to quantify sperm functional subpopulations by volFC could potentially implement the study of the relationship between sperm attributes and fertility.

Rational synthesis of total damage during cryoprotectant equilibration: modelling and experimental validation of osmomechanical, temperature, and cytotoxic damage in sea urchin (Paracentrotus lividus) oocytes

Sea urchins (e.g., Paracentrotus lividus) are important for both aquaculture and as model species. Despite their importance, biobanking of urchin oocytes by cryopreservation is currently not possible. Optimized cryoprotectant loading may enable novel vitrification methods and thus successful cryopreservation of oocytes. One method for determining an optimized loading protocol uses membrane characteristics and models of damage, namely osmomechanical damage, temperature damage (e.g., chill injury) and cytotoxicity. Here we present and experimentally evaluate existing and novel models of these damage modalities as a function of time and temperature. In osmomechanical damage experiments, oocytes were exposed for 2 to 30 minutes in hypertonic NaCl or sucrose supplemented seawater or in hypotonic diluted seawater. In temperature damage experiments, oocytes were exposed to 1.7 °C, 10 °C, or 20 °C for 2 to 90 minutes. Cytotoxicity was investigated by exposing oocytes to solutions of Me2SO for 2 to 30 minutes. We identified a time-dependent osmotic damage model, a temperature-dependent damage model, and a temperature and time-dependent cytotoxicity model. We combined these models to estimate total damage during a cryoprotectant loading protocol and determined the optimal loading protocol for any given goal intracellular cryoprotectant concentration. Given our fitted models, we find sea urchin oocytes can only be loaded to 13% Me2SO v/v with about 50% survival. This synthesis of multiple damage modalities is the first of its kind and enables a novel approach to modelling cryoprotectant equilibration survival for cells in general.

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.

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.

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.