Genetic and phenotypic variation in reproductive traits of AI boars

Swine fertility in a changing climate

Climate change has been linked to increasing temperatures and weather extremes. Certain regions around the world become more susceptible to environmental hazards that limit pig production and reproductive fertility. Environmental measures that link to pig fertility are needed to assess change, risk and develop solutions. Sub-populations of pigs display lower fertility in summer and are susceptible to heat stress. In the context of a warming climate, elevated temperatures and number of heat stress days increase body temperature and change the physiology, behavior, feed intake, and stress response of the pig. These changes could alter follicle development, oocyte quality, estrus expression, conception and litter size. In boars, sperm quality and production are reduced in response to summer heat stress. Nevertheless, while temperature increases have occurred over the years in some warmer locations, other regions have not shown those changes. Perhaps this involves the measures used for heat stress assessment or that climate is buffered in more temperate areas. Reductions in pig fertility are not always evident, and depend upon climate, year, genotype and management. This could also involve selection, as females more susceptible to heat stress and fertility failure, are subsequently culled. In the years from 1999 to 2020 when increases in global temperature from baseline occurred, measures of female fertility improved for farrowing rate and litter size. Progressive reduction in fertility may not be apparent in all geo-locations, but as temperatures increases become more widespread, these changes are likely to become more obvious and detectable.

Selection and direct biomarkers of reproductive capacity of breeding boars

Efficient management of pig reproduction is paramount for the sustainability and productivity of the global pork industry. Modern artificial insemination (AI) breeding programs have greatly benefited from the integration of advanced selection methods and biomarkers to enhance the reproductive performance of boars. While traditional selection methods have relied soley on boar phenotype, such as growth rate and conformation, modern pig breeding has shifted more and more toward molecular and genetic tools, which are still complemented by phenotypic traits. These methods encompass genomics, transcriptomics, and proteomics. Biomarkers serve as critical indicators of boar reproductive capacity. They can help to identify individuals with superior fertility and aid in the early identification of potential fertility issues, allowing for proactive management strategies. This review summarizes current knowledge of various biomarkers associated with semen quality, sperm function, and overall reproductive fitness in boars. Furthermore, we explore advanced technologies and their potential applications in uncovering novel selection methods and biomarkers for predicting boar fertility. A comprehensive understanding of selection criteria and biomarkers governing boar reproductive capacity is essential for developing effective breeding programs to enhance swine reproductive performance.

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.

Characterization of Extracellular Vesicle-Coupled miRNA Profiles in Seminal Plasma of Boars with Divergent Semen Quality Status

Sperm heterogeneity creates challenges for successful artificial insemination. Seminal plasma (SP) surrounding sperm is an excellent source for detecting reliable non-invasive biomarkers of sperm quality. Here, we isolated microRNAs (miRNAs) from SP-derived extracellular vesicles (SP-EV) of boars with divergent sperm quality statuses. Raw semen from sexually mature boars was collected for eight weeks. Sperm motility and normal morphology were analyzed, and the sperm was classified as poor- or good-quality based on standard cutoffs of 70% for the parameters measured. SP-EVs were isolated by ultracentrifugation and confirmed by electron microscopy, dynamic light scattering, and Western immunoblotting. The SP-EVs were subjected to total exosome RNA isolation, miRNA sequencing, and bioinformatics analysis. The isolated SP-EVs were round spherical structures approximately 30-400 nm in diameter expressing specific molecular markers. miRNAs were detected in both poor- (n = 281) and good (n = 271)-quality sperm, with fifteen being differentially expressed. Only three (ssc-miR-205, ssc-miR-493-5p, and ssc-miR-378b-3p) allowed gene targeting associated with cellular localization (nuclear and cytosol) and molecular functions (acetylation, Ubl conjugation, and protein kinase binding), potentially impairing sperm quality. PTEN and YWHAZ emerged as essential proteins for protein kinase binding. We conclude that SP-EV-derived miRNAs reflect boar sperm quality to enable therapeutic strategies to improve fertility.

Factors affecting the production of quality ejaculates from boars

Production of acceptable quality ejaculates in boars is dependent upon the Sertoli cell population established before puberty and how effectively these cells function after sexual maturity. In general, factors affecting Sertoli cell mitosis tend to have a two-fold greater effect on sperm production compared with those affecting spermatogenesis. Birthweight is a reliable indicator of in utero testicular development and prepubertal growth rates are positively correlated with testis size and sperm production after sexual maturity. Colostrum intake and pre-weaning nutrition account for much of the variation associated with quality and quantity of ejaculates and represent opportunities to further enhance lifetime sperm production. Interactions between young boars and humans, shortly after weaning, have important effects on spermatogenesis after sexual maturity and need to be studied further. The seasonal effect on depression in semen quality is the most significant factor affecting production of acceptable quality ejaculates after puberty. Ambient temperatures, greater than those of the thermoneutral zone, have both acute and chronic effects that compromise all aspects of the male reproductive axis. Identification of genes associated with heat-tolerant phenotypes holds promise for addressing this challenge, especially in light of the current trend in global warming. Supplementation of vitamins, minerals and other compounds have positive effects on sperm production during periods in which other stressors, especially heat stress, are present and is an important mitigation strategy. Recent information on housing conditions and boar usage patterns indicate these cause relatively minor changes in sperm production, overall, but for some males can have significant, long-term effects.

Cryo-scanning electron microscopy demonstrates that ice morphology is not associated with the post-thaw survival of domestic boar (Sus domesticus) spermatozoa: A comparison of directional and conventional freezing methods

Directional freezing (in 2 or 10 ml hollow glass tubes) has been reported to improve post-thaw sperm survival parameters compared to conventional methods (in 0.5 ml straws). However, the biophysical properties that increase post-thaw survival are poorly understood. Therefore, the aim for the current study was to investigate the effect of ice morphology on the post-thaw survival of domestic boar spermatozoa directionally and conventionally cryopreserved in 0.5 ml straws. Ice morphology was quantitatively analyzed using a combination of cryo-scanning electron microscopy and Fiji Shape Descriptors. Multivariate analysis found a significant, non-linear effect (p < 0.05) of interface velocity on ice morphology, with an increase in both ice-lake size, as indicated by area and in aspect ratio, at an interface velocity of 0.2 mm/s. By contrast, post-thaw sperm survival (defined as spermatozoa with both intact plasma membranes and acrosomes) was biphasic, with peaks of survival at interface velocities of 0.2 mm/s (54.2 ± 1.9%), and 1.0 or 1.5 mm/s (56.5 ± 1.5%, 56.7 ± 1.7% respectively), and lowest survival at 0.5 (52.1 ± 1.6%) and 3.0 mm/s (51.4 ± 1.9%). Despite numerical differences in Shape Descriptors, there was no difference (p > 0.05) in the post-thaw survival between conventionally and directionally cryopreserved samples at optimal interface velocities of 1.0 or 1.5 mm/s. These findings suggest that: 1) ice morphology has little impact on post-thaw survival of boar spermatozoa, and 2) directional freezing in 0.5 ml straws (rather than 2 or 10 ml hollow glass tubes) may attenuate benefits of directional freezing.

Effects of Heat Stress on Motion Characteristics and Metabolomic Profiles of Boar Spermatozoa

Heat stress (HS) commonly causes boar infertility and economic loss in the swine industry. The heat tolerance of boar semen presents obvious differences among individuals. However, whether heat stress affects motion characteristics and the metabolome profile in boar sperm remains unclear. In this study, the kinetic features of sperm from HS and non-HS (NHS) groups were detected by computer-assisted sperm analysis, and metabolomic profiling was performed by liquid chromatography−mass spectrometry. The results showed that heat stress significantly reduced sperm motility, average path distance (APD), straight-line velocity (VSL), straightness (STR), and linearity (LIN) (p < 0.05). A total of 528 and 194 metabolites in sperm were identified in the positive and negative ion modes, respectively. Lipids and lipid-like molecules, and organic acids and derivatives were major metabolic classes in the two modes. Furthermore, we separately identified 163 and 171 differential metabolites in the two modes between HS and NHS groups. Clustering analysis further revealed significant metabolic changes in sperm after heat stress. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that differential metabolites in the two modes were enriched in glycerophospholipid, choline, and alanine, aspartate, and glutamate and lysine metabolism. Taken together, these results demonstrate that heat stress can alter the motion characteristics and metabolomic profiles of boar sperm.

Seasonal variation in bull semen quality demonstrates there are heat-sensitive and heat-tolerant bulls

Using semen data from 1271 ejaculates (79 different bulls, 11 different breeds) we have investigated the variability of semen quality in cattle living in sub-tropical conditions. Modelling shows definitive evidence of seasonal variation. Semen quality from the same bulls had a 90% "pass rate" for cryopreservation purposes in winter, dropping to less than 50% in summer. Notably, individual bulls could be classified as either "heat-tolerant" (produce good quality spermatozoa all year regardless of temperature) or "heat-sensitive" (only produce good quality sperm in summer). Nominal logistic regression demonstrated when temperatures reach 30.5 °C, 40% of heat-sensitive bulls fail a semen analysis 17 days later. At 34 °C, the proportion of bulls failing reached 63%. Ratifying this, the purposeful heating of bulls to 40 °C for 12 h showed that individual animals had different degrees of heat-sensitivity. Using historical temperature data, we then modelled how many days/decade bulls would be subject to heat-events. Beginning from 1939 to 1949, on average, the area in which bulls were kept recorded 19, 7 and 1 day over 38 °C, 39 °C and 40 °C respectively. This number steadily increases and of last decade (2010-2010), the numbers of days per decade over 38 °C, 39 °C and 40 °C jumped to a staggering 75, 39 and 15 respectively. These data show the urgent need to identify heat-tolerant bulls as future sires. Such variation likely explains why the veterinary bull breeding test often fails to accurately predict bull breeding potential.

Comparative Proteomics and Phosphoproteomics Analysis Reveal the Possible Breed Difference in Yorkshire and Duroc Boar Spermatozoa

Sperm cells are of unique elongated structure and function, the development of which is tightly regulated by the existing proteins and the posttranslational modifications (PTM) of these proteins. Based on the phylogenetic relationships of various swine breeds, Yorkshire boar is believed to be distinctly different from Duroc boar. The comprehensive differential proteomics and phosphoproteomics profilings were performed on spermatozoa from both Yorkshire and Duroc boars. By both peptide and PTM peptide quantification followed by statistical analyses, 167 differentially expressed proteins were identified from 1,745 proteins, and 283 differentially expressed phosphopeptides corresponding to 102 unique differentially phosphorylated proteins were measured from 1,140 identified phosphopeptides derived from 363 phosphorylated proteins. The representative results were validated by Western blots. Pathway enrichment analyses revealed that majority of differential expression proteins and differential phosphorylation proteins were primarily concerned with spermatogenesis, male gamete generation, sperm motility, energy metabolism, cilium morphogenesis, axonemal dynein complex assembly, sperm–egg recognition, and capacitation. Remarkably, axonemal dynein complex assembly related proteins, such as SMCP, SUN5, ODF1, AKAP3, and AKAP4 that play a key regulatory role in the sperm physiological functions, were significantly higher in Duroc spermatozoa than that of Yorkshire. Furthermore, phosphorylation of sperm-specific proteins, such as CABYR, ROPN1, CALM1, PRKAR2A, and PRKAR1A, participates in regulation of the boar sperm motility mainly through the cAMP/PKA signal pathway in different breeds, demonstrating that protein phosphorylation may be an important mechanism underlying the sperm diversity. Protein–protein interaction analysis revealed that the 14 overlapped proteins between differential expression proteins and differential phosphorylation proteins potentially played a key role in sperm development and motility of the flagellum, including the proteins ODF1, SMCP, AKAP4, FSIP2, and SUN5. Taken together, these physiologically and functionally differentially expressed proteins (DEPs) and differentially expressed phosphorylated proteins (DPPs) may constitute the proteomic backgrounds between the two different boar breeds. The validation will be performed to delineate the roles of these PTM proteins as modulators of Yorkshire and Duroc boar spermatozoa.

Relationship between Fertility Traits and Kinematics in Clusters of Boar Ejaculates

Simple Summary

Swine reproduction efficiency is determined by the fertility potential of the sow and sperm quality. The objective of this study is to compare boar sperm motility and kinematic features to evaluate their relationships with reproductive success after artificial insemination (AI). In this study, the movement patterns of boar ejaculates were analyzed by a computer-assisted semen analysis (CASA)-Mot system, and the kinematic values of ejaculate clusters were assessed. The semen of the Pietrain boars showed more linear trajectory of the spermatozoa, while curvilinear velocity and oscillatory movement characterized the semen of the Duroc × Pietrain boars. The offspring of sows inseminated with Pietrain boars showed significantly lower number of stillbirths. In addition, ejaculate grouping into clusters did not have a predictive capacity on litter size variables. Nevertheless, the kinematic variables of the ejaculate may have a predictive, albeit reduced, capacity regarding litter size variables. The results of this study therefore open up possibilities for future assessments of fertility.

Abstract

The aim was to determine the relationship between kinematic parameters of boar spermatozoa and fertility rates of sow, as well as to assess the effect of sperm clusters on the fertility capacity of the ejaculate. Semen samples were collected from 11 sexually mature boars. Samples were analyzed by an ISAS^®v1 CASA-Mot system for eight kinematic parameters. Ejaculate clusters were characterized using multivariate procedures, such as principal factors (PFs) analysis and clustering methods (the k-means model). Four different ejaculate clusters were identified from two kinematic PFs which involved linear trajectory and velocity. There were differences (p < 0.05) between the sperm kinematic variables by sire line. There was no statistical difference (p > 0.05) between dam lines and ejaculate clusters in fertility variables. The discriminant ability of the different kinematics of sperm variables to predict litter size fertility was analyzed using receiver operating characteristics (ROC) curve analysis. Curvilinear velocity (VCL), average path velocity (VAP), amplitude of lateral head displacement (ALH), and beat-cross frequency (BCF) showed significant, albeit limited, predictive capacity for litter size fertility variables (range: 0.55–0.58 area under curve, AUC). The kinematic analysis of the ejaculates in clusters did not have a predictive capacity for litter size variables.

Seasonal Changes of Nuclear DNA Fragmentation in Boar Spermatozoa in Spain

Simple Summary

Artificial insemination is widely used in pig production and currently a boar performs several thousand matings per year. Traditionally sperm quality is focused on the number of spermatozoa, their motility and morphology. However, the quality of sperm DNA, which contains genetic information, is also related to fertility problems. The aim of this research was to study the effect of natural light hours and age of the boar on the status of the sperm DNA. After a powerful statistical analysis, it was found that the percentage of spermatozoa with fragmented DNA decreases within the observed age range as the boar gets older. On the other hand, the amount of spermatozoa with fragmented DNA was the lowest in autumn while it was the highest in summer. This study demonstrates the remaining seasonality of boars in Spain and highlights the importance of controlling the environmental conditions in the farms. Sperm DNA testing provides a basis for improving the selection of AI boars by excluding males with higher DNA fragmentation due to their very young reproductive age that may pose a potential subfertility.

Abstract

There are numerous cases when conventional spermiogram parameters are all within an acceptable range but boar subfertility persists. The total sperm nuclear DNA fragmentation index (tDFI) is a trait related to fertility and prolificacy problems that is not routinely evaluated in commercial AI boars. The aim of this research was to study the effect of the photoperiod, season and reproductive age of the boar on tDFI (measured by SCSA) of 1279 ejaculates from 372 different boars belonging to 6 different breeds located in 6 AI studs in Spain. tDFI data ranged from 0.018% to 20.1%. Although there was a significant single boar effect in the tDFI occurrence, a negative correlation between the tDFI and the age of the boar was found (p < 0.001). tDFI would decrease due to aging of the boar 0.66% each year old within the observed age range. After including age as a covariate in the ANCOVA, no differences were found in tDFI between photoperiods when the sperm collection date was evaluated. However, when the date of the production of semen in the testis was evaluated, the total percentage of spermatozoa with fragmented nuclear DNA was 1.46% higher in the increasing photoperiod in comparison to the decreasing photoperiod (p < 0.0001). On the other hand, for both dates, the lowest tDFI values corresponded to minimum day length for decreasing photoperiod phase (autumn), while the highest tDFI values were found in summer (maximum day length for decreasing photoperiod phase).

Susceptibility of boar spermatozoa to heat stress using in vivo and in vitro experimental models

Induction of heat stress as an experimental procedure in animals is commonly used to examine heat-related impacts on sperm quality. This study aimed to develop potential heat stress models that could be used at any time of the year, to advance the study of seasonal infertility in the pig under controlled conditions. Heat stress was induced by either housing boars (n = 6) at 30 °C inside a hot room for 42 days (55-65% humidity; LD 12:12 h; in vivo), or by heating boar semen (n = 7) for 30 min at various temperatures (35.5, 38.8, 40, 42, 46, 50, 54 and 60 °C; in vitro). Sperm motility was then characterized by computer-assisted sperm analysis (CASA; IVOS version 10: Hamilton Thorne, USA), and DNA integrity was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) and flow cytometry. Our in vivo hot room model induced biologically meaningful levels of DNA damage in boar spermatozoa (10.1 ± 1.9 hot room vs. 6.7 ± 1.7% control; P > 0.05), although not statistically significant from controls. Moreover, sperm concentration and motility parameters did not differ between treatments (P > 0.05). Compared to the 38.8 °C control, our in vitro heat shock model significantly increased sperm DNA damage after incubation at 54 and 60 °C (3.0 ± 1.0, 2.9 ± 1.0, 1.2 ± 0.3, 2.5 ± 0.7, 9.0 ± 3.7, 16.2 ± 7.1, 14.2 ± 5.8 and 41.8 ± 18.6% respectively; P ≤ 0.05). However, these temperatures rendered sperm completely immotile or dead, with most motility parameters declining rapidly to zero above 40 or 42 °C. In conclusion, our results suggest that temperature combined with individual factors may contribute to a boar's overall susceptibility to heat stress. Refinement of these models particularly of the in vitro heat shock model could be further pursued to overcome environmental variability, reduce whole animal experiments and provide a putative diagnostic fertility screening tool to evaluate heat tolerance in the boar.

Effects of the classification of boars according to progressive sperm motility and the extender type on the reproductive performance of a single fixed-time insemination

The study aimed to evaluate the fertility of boars according to the resistance of their semen to storage using dilution in either Short- or Long-term extender for single fixed-time insemination. From a total of 32 boars, twelve boars were classified during three semen collection (one collection/boar/week) as Low- (64.5%) or High-preservation (83.9%) capacity for maintaining progressive motility (PM) at 120 h of storage using Short-term extender. After the selection period, six ejaculates (weekly collected) from the Low- and High-preservation boars were diluted in Short- or Long-term extender (2 × 2 factorial design) for insemination and evaluation of fertility. A total of 519 weaned sows were submitted to induction of ovulation with triptorelin (OvuGel®) at 96 h post-weaning. Twenty-four hours later, estrus sows were single fixed-time inseminated (FTAI) with semen doses from the different groups of evaluation. The SAS® software was used for statistical analysis considering the class of boar, type of extender, and interaction as fixed effects. The GLIMMIX procedure was used, considering a binomial distribution for total motility (TM) and PM, binary distribution for pregnancy (PR), and farrowing rate (FR), and the total born (TB) was analyzed assuming a normal distribution with the comparison of means by Tukey-Kramer test. An interaction of class of boars and type of extender was observed for TM and PM at insemination (P < 0.001). Long-term extender increased TM in Low-preservation boars, with no effect in High-preservation boars. The ejaculates from High-preservation boars diluted in Short- or Long-term extender showed higher PM at insemination (86.8 and 87.8%, respectively) compared to those from Low-preservation boars in Short- or Long-term extender (73.2% and 77.9%, respectively). There was no effect of the interaction of boar preservation class and type of extender (P ≥ 0.163) on PR, FR or TB. However, Low-preservation boars presented lower TB (14.1 ± 0.2) compared to High-preservation boars (15.0 ± 0.2; P < 0.01). The PR (93.3 vs. 90.1) and FR (88.8 vs. 88.2) were not affected by class of Low- or High-preservation boars, respectively (P ≥ 0.187). The type of extender did not affect PR, FR, or TB (P ≥ 0.440). In conclusion, Low-preservation boars impaired the reproductive performance of single-FTAI sows by reducing TB with no apparent effect on PR or FR.

Shotgun proteome analysis of seminal plasma differentiate boars by reproductive performance

There is a need to identify subfertile boars before they enter into the breeding herd. Seminal plasma proteins are essential for normal sperm function and transport and play an important role in fertilization. The objective of this study was to use liquid chromatography tandem mass spectrometry for shotgun proteome analysis to investigate whether differences in boar fertility phenotype can be differentiated by seminal plasma protein abundance. Following 50 breedings, boars were categorized into one of four phenotypes: high farrowing rate and total born (HFHB; n = 9), high farrowing rate with low total born (HFLB; n = 10), low farrowing rate and total born (LFLB; n = 9), and low farrowing rate with high total born (LFHB; n = 4) that were distinct (p < 0.05) from each other by these variables. There were 506 proteins measured in at least one sample across all animals. There were 245 high confidence proteins and 56 were differentially abundant between the high fertility phenotype (HFHB) and at least one of the three subfertile groups. Findings support that seminal plasma protein profiles are distinct between boars with different fertility phenotypes.

Transcriptome analysis identifies genes and co-expression networks underlying heat tolerance in pigs

BACKGROUND

Heat stress adversely affects pig growth and reproduction performance by reducing feed intake, weight gain, farrowing rate, and litter size. Heat tolerance is an important characteristic in pigs, allowing them to mitigate the negative effects of heat stress on their physiological activities. Yet, genetic variation and signaling pathways associated with the biological processes of heat-tolerant pigs are currently not fully understood. This study examined differentially expressed genes and constructed gene co-expression networks on mRNAs of pigs under different heat-stress conditions using whole transcriptomic RNA-seq analyses. Semen parameters, including total sperm number per ejaculate, motility, normal morphology rate, droplets, and rejected ejaculate rate, were measured weekly on 12 boars for two time periods: thermoneutral (January to May), and heat stress (July to October). Boars were classified into heat-tolerant (n = 6) and heat-susceptible (n = 6) groups based on the variation of their ejaculate parameters across the two periods. RNA was isolated from the blood samples collected from the thermoneutral and heat stress periods for gene expression analysis.

RESULTS

Under heat stress, a total of 66 differentially expressed genes (25 down-regulated, 41 up-regulated) were identified in heat-tolerant pigs compared to themselves during the thermoneutral period. A total of 1041 differentially expressed genes (282 down-regulated, 759 up-regulated) were identified in the comparison between heat-tolerant pigs and heat-susceptible pigs under heat stress. Weighted gene co-expression network analysis detected 4 and 7 modules with genes highly associated (r > 0.50, p < 0.05) with semen quality parameters in heat-tolerant and heat-susceptible pigs under the effects of heat stress, respectively.

CONCLUSION

This study utilized the sensitivity of semen to heat stress to discriminate the heat-tolerance ability of pigs. The gene expression profiles under the thermoneutral and heat stress conditions were documented in heat-tolerant and heat-susceptible boars. Findings contribute to the understanding of genes and biological mechanisms related to heat stress response in pigs and provide potential biomarkers for future investigations on the reproductive performance of pigs.

A new paradigm regarding testicular thermoregulation in ruminants?

Increased testicular temperature reduces percentages of morphologically normal and motile sperm and fertility. Specific sperm defects appear at consistent intervals after testicular hyperthermia, with degree and duration of changes related to intensity and duration of the thermal insult. Regarding pathogenesis of testicular hyperthermia on sperm quality and fertility, there is a long-standing paradigm that: 1) testes operate near hypoxia; 2) blood flow to the testes does not increase in response to increased testicular temperature; and 3) an ensuing hypoxia is the underlying cause of heat-induced changes in sperm morphology and function. There are very limited experimental data to support this paradigm, but we have data that refute it. In 2 × 3 factorial studies, mice and rams were exposed to two testicular temperatures (normal and increased) and three concentrations of O₂ in inspired air (hyperoxia, normoxia and hypoxia). As expected, increased testicular temperature had deleterious effects on sperm motility and morphology; however, hyperoxia did not prevent these changes nor did hypoxia replicate them. In two follow-up experiments, anesthetized rams were sequentially exposed to: 1) three O₂ concentrations (100, 21 and 13% O₂); or 2) three testicular temperatures (33, 37 and 40 °C). As O₂, decreased, testis maintained O₂ delivery and uptake by increasing testicular blood flow and O₂ extraction, with no indication of anaerobic metabolism. Furthermore, as testicular temperature increased, testicular metabolic rate nearly doubled, but increased blood flow and O₂ extraction prevented testicular hypoxia and anaerobic metabolism. In conclusion, our data, in combination with other reports, challenged the paradigm that testicular hyperthermia fails to increase testicular blood flow and the ensuing hypoxia disrupts spermatogenesis.

Effects of increased levels of supplemental vitamins during the summer in a commercial artificial insemination boar stud

Heat stress due to increasing extremes in ambient temperature and humidity results in reduced semen quality in boars. This has caused reduced efficiency of the swine industry, requiring more boars to breed the same number of sows. Vitamins such as vitamin C (VC) and E (VE) have been shown to improve semen quality in boars. Recently, vitamin D has been shown to improve semen quality in boars. The purpose of this experiment was to evaluate the effects of increased supplemental vitamins on boar reproduction during the summer season in a commercial boar stud. One hundred and sixty Pig Improvement Company (PIC) terminal line boars (n = 32 per treatment) and 39 maternal, heat-sensitive boars (n = 7 or 8 per treatment) were randomly allocated to treatment and fed a corn and soybean meal-based diet adjusted based on individual boar body condition score. A control (CNT) diet was used that met PIC recommendations for boars. Increased supplementation of specific vitamins was given in the form of a top-dress and consisted of CNT wheat middlings, CNT plus VC (560 mg/day), CNT plus 25-hydroxy vitamin D3 (VD) (125 µg/day), CNT plus VE (275 mg/day) and CNT plus VC, VD and VE (CDE). The experiment was split into three periods based on maximum daily high temperatures in the barn, where period 1 was weeks 1 to 4, period 2 was weeks 5 to 11 and period 3 was weeks 12 to 14. Semen was collected from boars as needed using the stud's normal production schedule and was analyzed for sperm quantity and quality characteristics. There were no dietary effects on semen volume, sperm concentration or total sperm production (P ≥ 0.553). Total motility of sperm was not impacted by diet (P = 0.115); although, VC tended (P = 0.064) to have a greater progressive motility than CDE. Percentages of morphologically normal sperm and normal acrosomes were not affected by dietary supplementation (P ≥ 0.157). Period effects were observed for most semen quality parameters, with quality generally becoming reduced over time. The present study demonstrates that increased supplementation of vitamins beyond PIC recommendations was not beneficial for boar reproduction during the summer.

Effects of season on boar semen parameters and antioxidant enzymes in the south subtropical region in Brazil

Although boar semen productivity is affected by seasonality, its effects are not equal among different regions which raise concerns regarding the profitability of boar stud farms. Therefore, the goals of this study were (i) to evaluate the seasonal effect on semen production in a commercial boar stud farm located in a subtropical climate region and (ii) to verify whether the activities of superoxide dismutase and glutathione peroxidase in spermatozoa and seminal plasma were associated with seminal traits of fresh and cooled semen. Nine boars were collected twice per season, and routine seminal parameter analyses were performed together with superoxide dismutase and glutathione peroxidase activities in seminal plasma and spermatozoa. Despite a reduction in sperm concentration in spring and summer, most seminal parameters were constant year-round. Temperature-humidity index was higher in the summer compared to spring, autumn and winter (p < .05). Superoxide dismutase activity in spermatozoa was increased in summer compared to autumn and winter (p < .05). The activities of both enzymes in seminal plasma and spermatozoa glutathione peroxidase remained unaltered throughout the seasons. In conclusion, seasonality showed little influence in overall boar seminal parameters despite microclimatic differences among seasons, and spermatozoa collected during summer increased superoxide dismutase activity.

Cluster analysis reveals seasonal variation of sperm subpopulations in extended boar semen

This study aimed to identify motile sperm subpopulations in extended boar semen and to observe the presumptive seasonal variation in their distribution. Data from 4837 boar ejaculates collected over a two-year period were analyzed in terms of kinematic parameters by Computer Assisted Sperm Analysis (CASA). Individual sperm data were used to determine subgroups of motile sperm within the ejaculates using cluster analysis. Four motile sperm subpopulations (SP) were identified, with distinct movement patterns: SP1 sperm with high velocity and high linearity; SP2 sperm with high velocity but low linearity; SP3 sperm with low velocity but high linearity; and SP4 sperm with low velocity and low linearity. SP1 constituted the least overall proportion within the ejaculates (P < 0.05). Season of semen collection significantly influenced the different proportions of sperm subpopulations. Spring was characterized by similar proportions of SP1 and SP4 (NS) and higher proportions of SP3. Summer brought a decrease in both subgroups containing fast sperm (SP1 and SP2) (P < 0.05). During autumn, increases in SP2 and SP4 were recorded. Winter substantially affected the proportions of all sperm subpopulations (P < 0.05) and SP2 became the most represented subgroup, while SP1 (fast and linear) reached its highest proportion compared to other seasons. In conclusion, extended boar semen is structured in distinct motile sperm subpopulations whose proportions vary according to the season of collection. Summer and autumn seem to have a negative impact on the fast and linear subpopulation. Cluster analysis can be useful in revealing differences in semen quality that are not normally detected by classical evaluation based on mean values.

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.

Boar genotype as a factor shaping age-related changes in semen parameters and reproduction longevity simulations

The aim of this study was a detailed analysis of the boar genotypes used in AI stations with an indication of their production capacity, including age and a precise analysis of their culling time and reason. The study included 334 boars: 81 Polish Large White (PLW), 108 Polish Landrace (PL), 49 Pietrain (P), 56 Duroc × Pietrain (D × P) and 40 Hampshire × Pietrain (H × P). Semen volume, spermatozoa concentration, total number of spermatozoa, number of motile spermatozoa, and number of insemination doses were analyzed. Quadratic regression was used to illustrate the selected sperm parameters at specific ages. Among all the studied boars the lowest motilities of spermatozoa were identified in white breeds PLW and PL, and the difference between motility extremes was 3.53% (P ≤ 0.01). The highest number of insemination doses were produced from D × P crossbreed boars: about 0.7 portions more compared to PL, 1.13 to PLW, 1.18 to H × P and 1.8 to P (all differences P ≤ 0.01). It has been shown in the case of ejaculate volume that for PLW and H × P boars the culling moment was far too early in terms of production capacity and differences were, respectively, 16.35 ml for PLW and 12.61 ml for H × P. Based on the developed regression equations, the earliest maximum number of motile sperm (73.82 × 10⁹) was obtained by H × P crossbreed boars as early as at age 24 months. The highest values for this parameter were achieved, however, by other D × P crossbreed boars: 74.30 × 10⁹ at the later age of 32 months. A consequence of the high number of motile sperm in young H × P boars was that the theoretical maximum value of the number of AI doses was produced as early as the 14th month (25.59 portions). Curves of similar shape were obtained for PL and D × P boars; the difference in maximal values was 0.54 portions in favor of crossbreeds, at a later age of 7 months. It was noted that for PLW and D × P boars the highest number of cullings were due to reduced demand (24.47% and even 31.19%, respectively). Other boars - PL, P and H × P - were most frequently culled because of low semen values. Regardless of the genotype, high survival probabilities (over 0.96) were noted for the age of 12 months. The highest probabilities (still over 0.96) were noted in the longest time period (up to 18 months) for P boars. The results of our study can be used in AI stations as reference points for the exploitation and culling of boars with different genotypes.

Revisiting summer infertility in the pig: could heat stress-induced sperm DNA damage negatively affect early embryo development?

Temperature is a crucial factor in mammalian spermatogenesis. The scrotum, pampiniform plexus, and cremaster and dartos muscles in mammals are specific adaptations to ensure sperm production in a regulated environment 4−6°C below internal body temperature. However, the limited endogenous antioxidant systems inherent in mammalian spermatozoa compounded by the loss of cytosolic repair mechanisms during spermatogenesis, make the DNA in these cells particularly vulnerable to oxidative damage. Boar sperm is likely to be more susceptible to the effects of heat stress and thus oxidative damage due to the relatively high unsaturated fatty acids in the plasma membrane, low antioxidant capacity in boar seminal plasma, and the boar’s non-pendulous scrotum. Heat stress has a significant negative impact on reproductive performance in piggeries, which manifests as summer infertility and results in productivity losses that amount to millions of dollars. This problem is particularly prevalent in tropical and subtropical regions where ambient temperatures rise beyond the animal’s zone of thermal comfort. Based on preliminary studies in the pig and other species, this article discusses whether heat stress could induce sufficient DNA damage in boar sperm to significantly contribute to the high rates of embryo loss and pregnancy failure observed in the sow during summer infertility. Heat stress-induced damage to sperm DNA can lead to disrupted expression of key developmental genes essential for the differentiation of early cell lineages, such as the trophectoderm, and can distort the timely formation of the blastocyst; resulting in a failure of implantation and ultimately pregnancy loss. Confirming such a link would prompt greater emphasis on boar management and strategies to mitigate summer infertility during periods of heat stress.

The dependence of the growth rate and meat content of young boars on semen parameters and conception rate

Boars have a decisive impact on the progress in pig production, however, there is no recent information about the optimal growth parameters during the rearing period for modern breed later used in artificial insemination (AI) stations. Therefore, the objective of the research was to conduct semen parameter and conception rate analyses on the basis of growth rate and meat content assessments made during the rearing of AI boars of different genotypes. The study was carried out between 2010 and 2014 and included 184 boars in five breed combinations: 46 Polish Large White, 50 Polish Landrace, 27 Pietrain, 36 Duroc×Pietrain and 25 Hampshire×Pietrain. Boars were qualified by daily gains and meat content assessment (between 170 and 210 days of life). A total number of 38 272 ejaculates were examined (semen volume (ml), spermatozoa concentration (×106 ml-1), total number of spermatozoa (×109) and number of insemination doses from one ejaculate (n)). The fertility was determined by the conception rate (%). Semen volume, spermatozoa concentration and conception rate (P<0.01), followed by the total number of spermatozoa and insemination doses (P<0.05) were characterized by the highest variability in relation to breed of boars. The effect of daily gains was reported for spermatozoa concentration, number of insemination doses, conception rate (all P<0.01) and total number of spermatozoa (P<0.05). The peak of growth for spermatozoa concentration, total number of spermatozoa, insemination doses and conception rate was achieved for 800 to 850 g gains. Meat content affected semen volume, number of insemination doses and conception rate (P<0.05). Rearing boars while maintaining daily gains at the 800 to 850 g level and 62.5% to 65% meat content helps AI stations to increase the efficiency and economic profitability, and the number of insemination doses to increase by up to 300 doses/boar within a year. The analyses of growth parameters may help increase the efficiency and economic viability of AI stations.

Age and seasonal-dependent variations in the biochemical composition of boar semen

This study investigated the effect of age- and seasonal-related variations in the composition of boar semen over a 3-year period. At the onset of 8 months of age, ejaculates were collected from four boars and allocated into three groups: 8 to 18, 19 to 30, and 31 to 42 months and were divided into two seasonal periods: autumn-winter and spring-summer. Boar variability had a significant effect on most of the analyzed semen parameters. Significantly, higher ejaculate volumes were observed in the boars older than 18 months of age during the autumn-winter period. Sperm concentration was higher in boars less than the age of 18 months of age, whereas the total sperm numbers were significantly higher during the autumn-winter period, regardless of the age group. Seasonal effects in sperm motility were more marked in boars at the age of 19 to 30 months, being significantly higher during the autumn-winter period. The proportions of spermatozoa with intact, normal apical ridge acrosome, and osmotically tolerant acrosomal membranes were markedly higher in boars at the age of 19 to 30 months during the autumn-winter period. Spermatozoa harvested during the spring-summer period were more susceptible to lipid peroxidation, irrespective of the age group. Significantly, higher levels of protein content and concentrations of nonthiol-containing antioxidant components of the seminal plasma (SP) were detected in boars less than 18 months of age during the autumn-winter period. Seasonal effects on the pH and proteinase inhibitory activity in the SP were more marked in boars less than 18 months of age, whereas alkaline phosphatase activity was greater in boars at the age of 19 to 30 months during the autumn-winter period. Substantial amounts of the thiol-containing antioxidants of the SP were detected in boars older than 18 months of age during the spring-summer period. Neither osmolality nor total antioxidant status was affected by differences in the seasonal periods or age groups. The findings of this study indicate that age- and seasonal-related variations affect the reproductive tract functions in the boar, resulting in marked changes in the biochemical composition of the semen.

Field study analysis of the influences of deworming regimens and housing conditions on parasites and sperm output in 21 European boar studs

The current study reports the parasitological results of a quality control audit in 21 European boar studs. Field investigations were performed over a 2-year period (2012-2013) during the winter and spring. From each stud, an average of 30 (range, 25-33) individual faecal samples and ejaculates from 615 randomly selected Pietrain boars were analysed. Statistical analysis revealed a significant effect (P < 0.0001) of deworming regimen (DR) × age class of boar (A) and housing condition (H) × A on the presence of parasites. A second model indicated a significant effect (P = 0.0262) of DR × H × A on the presence of parasites. Sperm output was significantly affected (P < 0.0001) by the DR. Based on this study, recommendations for deworming AI boars are proposed.

Artificial insemination in pigs today

Use of artificial insemination (AI) for breeding pigs has been instrumental for facilitating global improvements in fertility, genetics, labor, and herd health. The establishment of AI centers for management of boars and production of semen has allowed for selection of boars for fertility and sperm production using in vitro and in vivo measures. Today, boars can be managed for production of 20 to 40 traditional AI doses containing 2.5 to 3.0 billion motile sperm in 75 to 100 mL of extender or 40 to 60 doses with 1.5 to 2.0 billion sperm in similar or reduced volumes for use in cervical or intrauterine AI. Regardless of the sperm dose, in liquid form, extenders are designed to sustain sperm fertility for 3 to 7 days. On farm, AI is the predominant form for commercial sow breeding and relies on manual detection of estrus with sows receiving two cervical or two intrauterine inseminations of the traditional or low sperm doses on each day detected in standing estrus. New approaches for increasing rates of genetic improvement through use of AI are aimed at methods to continue to lower the number of sperm in an AI dose and reducing the number of inseminations through use of a single, fixed-time AI after ovulation induction. Both approaches allow greater selection pressure for economically important swine traits in the sires and help extend the genetic advantages through AI on to more production farms.

Individual and seasonal variations in the quality of fractionated boar ejaculates

Reproductive seasonality has been shown to affect the quality of boar semen. In this study, effects of seasonal variations in the characteristics of spermatozoa and seminal plasma (SP) of fractioned ejaculates from individual boars have been investigated. Fractionated ejaculates, designated as fraction 1 (F1), fraction 2 (F2), and fraction 3 (F3), were collected from five mature boars during the autumn-winter (October through March) and spring-summer periods (April through September). A total of 10 fractionated ejaculates (F1, F2, and F3) were collected from each boar within each seasonal period. Assessments of the sperm quality characteristics included computer-assisted sperm analysis motion patterns, mitochondrial membrane potential (MMP), plasma membrane integrity, normal apical ridge acrosomes, and DNA fragmentation. Besides SDS-PAGE and densitometric analyses of the SP proteins, the antiperoxidant activity was monitored. There were marked differences in the sperm quality characteristics among the boars, except for sperm MMP. Distinct seasonal differences (P < 0.05) were observed in the ejaculate volume of F3 during the autumn-winter and spring-summer periods (107.78 ± 5.45 and 87.80 ± 4.75 mL, respectively). Significantly higher (P < 0.05) sperm concentration and the total number of spermatozoa in the fraction were observed during the autumn-winter period. Seasonal effects in MMP and plasma membrane integrity were manifested in significantly higher (P < 0.05) percentages of spermatozoa with functional mitochondria and intact plasma membrane during the autumn-winter period. However, the seasonal effects were less marked in either sperm normal apical ridge acrosomes or sperm DNA fragmentation. Sodium dodecyl sulfate-PAGE and densitometric analyses revealed marked variations in the protein composition of the SP profiles among the boars, regardless of the ejaculate fraction and seasonal period. Distinct seasonal variations, observed in the SDS-PAGE profiles, were associated with an abundance of protein fractions of low-molecular and high-molecular weight components, particularly during the autumn-winter period. There were wide variations in antiperoxidant activity in the SP among the boars, being significantly higher in the autumn-winter period, irrespective of the ejaculate fraction. It can be suggested that marked deterioration of the quality of fractionated ejaculates during the spring-summer period was probably caused by impaired reproductive function in the boar.

Impact of swine reproductive technologies on pig and global food production

Reproductive technologies have dramatically changed the way pigs are raised for pork production in developed and developing countries. This has involved such areas as pigs produced/sow, more consistent pig flow to market, pig growth rate and feed efficiency, carcass yield and quality, labor efficiency, and pig health. Some reproductive technologies are in widespread use for commercial pork operations [Riesenbeck, Reprod Domest Anim 46:1-3, 2011] while others are in limited use in specific segments of the industry [Knox, Reprod Domest Anim 46:4-6, 2011]. Significant changes in the efficiency of pork production have occurred as a direct result of the use of reproductive technologies that were intended to improve the transfer of genes important for food production [Gerrits et al., Theriogenology 63:283-299, 2005]. While some technologies focused on the efficiency of gene transfer, others addressed fertility and labor issues. Among livestock species, pig reproductive efficiency appears to have achieved exceptionally high rates of performance (PigCHAMP 2011) [Benchmark 2011, Ames, IA, 12-16]. From the maternal side, this includes pigs born per litter, farrowing rate, as well as litters per sow per year. On the male side, boar fertility, sperm production, and sows served per sire have improved as well [Knox et al., Theriogenology, 70:1202-1208, 2008]. These shifts in the efficiency of swine fertility have resulted in the modern pig as one of the most efficient livestock species for global food production. These reproductive changes have predominantly occurred in developed countries, but data suggests transfer and adoption of these in developing countries as well (FAO STAT 2009; FAS 2006) [World pig meat production: food and agriculture organization of the United Nations, 2009; FAS, 2006) Worldwide Pork Production, 2006]. Technological advancements in swine reproduction have had profound effects on industry structure, production, efficiency, quality, and profitability. In all cases, the adoption of these technologies has aided in the creation of a sustainable supply of safe and affordable pork for consumers around the world [den Hartog, Adv Pork Prod 15:17-24, 2004].

Using the product threshold model for estimating separately the effect of temperature on male and female fertility

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.

Assessment of pubertal development of boars derived from ultrasonographic determination of testicular diameter

At the onset of puberty, seminiferous tubules rapidly increase in diameter, thereby occupying a greater proportion of the testis, resulting in a rapid increase in testicular size. The objective of the current studies was to evaluate ultrasonography for assessing testicular diameter, as a basis for ranking boars relative to their extent of pubertal development. In the initial study, prior to castration at 4, 5, 6, or 7 mo of age, testicular length and diameter were assessed by ultrasonography in 160 anesthetized boars. After castration, testes were weighed. Mean diameter of seminiferous tubules and percentage of the testis occupied by tubules were determined by histological evaluations of all testes. Testicular volume was calculated from length and diameter and was correlated with testicular weight (P < 0.001; r ≧ 0.78) within each of the four age groups. At 4 and 5 mo of age, testicular diameter correlated positively (P < 0.001) with diameter of seminiferous tubules; this relationship was not significant at older ages. In two subsequent studies, testicular diameter determined ultrasonographically in conscious boars was highly correlated (r > 0.8) when assessed twice on the same day, or when diameter of the right was compared with diameter of the left testis. Similarly, testicular diameter obtained initially at 92 d of age correlated positively (P < 0.001) with the diameter observed at older ages, but the magnitude of the relationship decreased as time between evaluations increased. These findings supported ultrasonographic determination of testicular diameter during early pubertal development, as a means to rank boars of similar chronological age for extent of pubertal development.

Effects of heat stress on mammalian reproduction

Heat stress can have large effects on most aspects of reproductive function in mammals. These include disruptions in spermatogenesis and oocyte development, oocyte maturation, early embryonic development, foetal and placental growth and lactation. These deleterious effects of heat stress are the result of either the hyperthermia associated with heat stress or the physiological adjustments made by the heat-stressed animal to regulate body temperature. Many effects of elevated temperature on gametes and the early embryo involve increased production of reactive oxygen species. Genetic adaptation to heat stress is possible both with respect to regulation of body temperature and cellular resistance to elevated temperature.