New trends in production management in European pig AI centers

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

In vitro aging of boar spermatozoa: role of sperm proximity and seminal plasma

BACKGROUND

Knowledge on the effect of seminal plasma on sperm function in extended semen during in vitro storage is lacking.

OBJECTIVES

The aim was to examine the interactive role of sperm concentration and seminal plasma concentration on boar sperm function during in vitro aging.

MATERIAL AND METHODS

Experiment 1: Twenty-one boar ejaculates were aliquoted with Beltsville Thawing Solution into five semen doses containing between 32.5 and 8.5 × 10⁶  sperm/mL. Experiment 2: Semen samples (n = 8) containing 18 × 10⁶ or 10 × 10⁶  sperm/mL with their natural amount of seminal plasma and 10 × 10⁶  sperm/mL substituted with autologous seminal plasma to the same concentration as in doses with 18 × 10⁶  sperm/mL were prepared. Experiment 3: Four variants of semen doses containing 18 × 10⁶ or 10 × 10⁶  sperm/mL with either 10% or 0.5% (v/v) seminal plasma were used. Lipid peroxidation was assessed using Bodipy 581/591 in samples (n = 8) with two different sperm concentrations. Semen was examined during 144-h storage at 17 °C by computer-assisted semen analysis and flow cytometry.

RESULTS

Experiment 1: 3D kinematic patterns revealed a concentration- and time-dependent loss of sperm kinematics in samples with < 23 × 10⁶  sperm/mL (p < 0.05). Percent viable spermatozoa with high mitochondria membrane potential were lower (p < 0.05) in samples with < 15 × 10⁶  sperm/mL. Experiment 2: Seminal plasma supplementation in samples with 10 × 10⁶  sperm/mL did not restore the loss of sperm kinematics (p > 0.05). Experiment 3: At 144 h, motility was lowest in samples containing 10 × 10⁶  sperm/mL and 10% (v/v) seminal plasma (p < 0.05). Sperm lipid peroxidation did not differ between samples with different sperm concentration.

CONCLUSION

Long-term exposure to seminal plasma has a negative impact on in vitro-aged boar spermatozoa. Reduced sperm-to-sperm proximity but not the reduction of seminal plasma limits sperm function in long-term stored boar semen.

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

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

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

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

Centrifugation stress reduces the responsiveness of spermatozoa to a capacitation stimulus in in vitro-aged semen

Density gradient centrifugation of semen is commonly used in many assisted reproduction techniques. Although gradients have the potential to isolate and enrich motile and viable spermatozoa, the centrifugation force presents a stress factor to cell organelles and membranes. The objective of the study was to evaluate the impact of density gradient centrifugation stress on sperm capacitation dynamics, cell stability and the ability of spermatozoa to specifically respond to bicarbonate in extended semen undergoing in vitro ageing. Extended boar semen (n = 7) was stored for 12, 24, 72 and 120 h respectively at 17 °C before centrifugation and incubation in variations of an in vitro capacitation medium. The number of viable, acrosome intact sperm and motility parameters as assessed by computer-assisted semen analysis did not change during storage. Kinetic changes in viability (plasma membrane integrity) and intracellular calcium levels (calcium influx) during in vitro capacitation were assessed after preparation of semen samples with both, a Percoll and a sucrose gradient centrifugation, either only Percoll, only sucrose centrifugation or no centrifugation. Changes in the viable sperm population that could be specifically attributed as a response to either bicarbonate or calcium were determined. In in vitro-aged (>12 h stored) spermatozoa, centrifugation reduced the proportion of spermatozoa which specifically responded to the capacitating stimulus bicarbonate. Concomitantly, centrifugation increased the proportion of spermatozoa responding to calcium in absence of bicarbonate, thus indicating an increased sensitivity to incubation per se. Absence of centrifugation steps during semen preparation, revealed a highly conserved ability of in vitro-aged spermatozoa to specifically respond to bicarbonate. In conclusion, density gradient centrifugation alters the physiological property of spermatozoa for controlled capacitation, which may influence the success rates of centrifuged semen in assisted reproductive technologies and confound interpretation of capacitation assays.

Liquid storage of boar semen: Current and future perspectives on the use of cationic antimicrobial peptides to replace antibiotics in semen extenders

Antibiotics are of great importance in boar semen extenders to ensure long shelf life of spermatozoa and to reduce transmission of pathogens into the female tract. However, the use of antibiotics carries a risk of developing resistant bacterial strains in artificial insemination laboratories and their spread via artificial insemination. Development of multiresistant bacteria is a major concern if mixtures of antibiotics are used in semen extenders. Minimal contamination prevention techniques and surveillance of critical hygiene control points proved to be efficient in reducing bacterial load and preventing development of antibiotic resistance. Nevertheless, novel antimicrobial concepts are necessary for efficient bacterial control in extended boar semen with a minimum risk of evoking antibiotic resistance. Enhanced efforts have been made in recent years in the design and use of antimicrobial peptides (AMPs) as alternatives to conventional antibiotics. The male genital tract harbors a series of endogenic substances with antimicrobial activity and additional functions relevant to the fertilization process. However, exogenic AMPs often exert dose- and time-dependent toxic effects on mammalian spermatozoa. Therefore, it is important that potential newly designed AMPs have only minor impacts on eukaryotic cells. Recently, synthetic magainin derivatives and cyclic hexapeptides were tested for their application in boar semen preservation. Bacterial selectivity, proteolytic stability, thermodynamic resistance, and potential synergistic interaction with conventional antibiotics propel predominantly cyclic hexapeptides into highly promising, leading candidates for further development in semen preservation. The time scale for the development of resistant pathogens cannot be predicted at this moment.

The specific response to capacitating stimuli is a sensitive indicator of chilling injury in hypothermically stored boar spermatozoa

Boar spermatozoa are sensitive to storage temperatures below 15 °C. Chilling injury causes loss of motility and membrane integrity in a minority of cells, whereas the main population displays sublethal changes compromising fertility. In this study, changes of the response to capacitation conditions in hypothermically stored boar spermatozoa have been examined using a kinetic approach with well-defined test and control media. Ejaculates of seven boars were diluted in Beltsville Thawing Solution kept for 3 h at 22 °C or cooled to 17, 10 and 5 °C and stored for 24 and 96 h. At each time point, the standard sperm parameters motility and membrane integrity were evaluated. Subsequently, washed subsamples were incubated in capacitating and control medium before flow cytometric analysis of intracellular calcium content using the Fluo-3 probe and changes in phospholipid disorder using merocyanine. Kinetic changes of response parameters were monitored in viable (plasma membrane intact) cells. Chilling led to a loss of standard sperm quality traits in a minor subpopulation of cells, whereas storage length had no effect on these parameters. However, responses to incubation as determined by the loss of live cells with low intracellular calcium content showed marked changes in relation to storage conditions. The specific responsiveness to capacitation conditions decreased in close relation to storage temperature and length. In contrast, the merocyanine probe revealed to be limited to detect effects of hypothermic storage. Using Fourier transform infrared spectroscopy, no influence of chilling on membrane phase behaviour was found that might implicate decreased sperm function. In conclusion, assessment of response to capacitating media by monitoring intracellular calcium levels provides a sensitive measure for chilling injury in extended boar semen, and therefore, deserves implementation in hypothermic storage tests.

243 IMPACT OF MATERNAL LOW-DOSE ESTRADIOL-17β EXPOSURE DURING PREGNANCY ON THE REPRODUCTIVE ORGANS OF MALE PIG PROGENY

In male developing piglets, low endogenous oestrogenic hormone levels prevail. Sensitive tissues expressing high levels of oestrogen receptors, such as the epididymis, might thus be of specific relevance for early disturbances by estrogenic endocrine disruptors. We have previously shown that distinct concentrations of the natural oestrogen oestradiol-17β (E2) orally applied during the whole period of pregnancy in sows lead to a distinct shift in body composition. Therefore, we aimed at investigating whether prenatal E2 exposure had the potential to program male reproductive organs toward altered semen quality. The E2 treatment groups (n = 4 sows/group) were designed to represent doses of pharmacological relevance (PR; 1000 µg kg–1 of body weight per day), oral no-effect level (10 µg kg–1 of body weight per day), and acceptable daily intake level (0.05 µg kg–1 of body weight per day). Total RNA was extracted from the epididymis of 8-week-old piglet twins (n = 2 per sow). The RNA of littermates was pooled and subjected to microarray analysis (MA) using Agilent Porcine Genome Arrays (Agilent Technologies Inc., Santa Clara, CA, USA). Ejaculates of adult male pigs from the control group and the pharmacological group (n = 4) were collected and analysed for quantitative and qualitative parameters by using computer-assisted sperm analysis and flow cytometry. In total, 105 transcripts exhibited a significant difference of more than 1.5-fold for at least one of the treatment groups compared with the control group (P < 0.05; FDR 5%). Several transcripts revealed gradually decreasing amounts subject to the dose of E2 exposure. Eight transcripts showed significant differences in all 3 treatment groups compared with the control group. Thirty-two transcripts had reduced abundance in the PR group and the oral no-effect level group, whereas 20 transcripts were downregulated in the PR group only. Semen parameters of adult males did not differ regarding volume and semen concentration, morphology, and membrane integrity. Computer-assisted sperm analysis evaluations did not show differences in motility and other kinematic parameters. Eight weeks after E2 exposure, male prepubertal piglets exhibited significant differences in epididymal messenger RNA transcript abundance subject to an in utero E2 treatment. This points toward possible epigenetic programming of the epididymis. Although the differential transcript abundance indicates a perturbation, normal semen quality was found after adolescence. Either these transcriptional changes are of minor functional importance or flexible mechanisms account for the developmental adaptations. Considering that identical transcripts were regulated in offspring exposed to both pharmacological and very low doses, further investigations of set points obviating long-term adverse consequences are needed.

Recent advances in boar semen cryopreservation

Since 35 years ago boar semen has been frozen and used for artificial insemination (AI). However, fertility of cryopreserved porcine sperm has consistently been low as boar sperm are more sensitive to cellular stress imposed by changing osmotic balance, oxidative stress, low-temperature exposure, cryo-protectant intoxication etc. and are less able to compensate for these deficiencies at commercially applicable dosages. Additionally, differences in sperm freezability among individuals are well known. Here we review current advances on tests to screen sperm quality post-thaw, on ways of diminishing individual boar effects, on improvement of cryo-protection by novel extender components, on packaging and freezing protocols and freezing and thawing methods, and on the handling of sexed boar sperm. Major advances have been registered, which have improved cryo-survival and the capacity to process boar semen for commercial AI.

Immunological responses to semen in the female genital tract

When spermatozoa, seminal plasma and semen extender reach the uterus and interact with local leukocytes and endometrial cells, several immune mechanisms are initiated which have immediate, mid-term and long-term effects on ovulation, sperm cell selection, fertilization and pregnancy success by assuring the acceptance of fetal tissues. This report gives an overview on relevant key immune mechanisms following roughly the time axis after insemination. Detailed knowledge regarding these mechanisms will aid maximizing reproductive efficiency in livestock production. In the future, the many species involved will require a more comparative approach, since evidence is growing that endometrial physiology and the response to varying amounts and compositions of seminal plasma, various semen extenders, and variable numbers of spermatozoa also provoke different immune responses.

Determinants of sperm quality and fertility in domestic species

Fertilization success cannot be attributed solely to the absolute number of vital, motile, morphologically normal spermatozoa inseminated into the female but more especially to their functional competence. A range ofin vitrotests has therefore been developed to monitor crucial aspects of sperm function: their ability to adapt to changing osmotic conditions, to bind to the oviductal epithelium, and to undergo capacitation in an appropriate and timely manner. The tests employ flow cytometry in conjunction with fluorescent techniques, electronic cell counting, and computer-assisted image area analysis. The highly quantitative analysis provided by electronic sizing and flow cytometry enables assessment of representative cell numbers in a very short time with high reproducibility. More importantly, it allows the detection of physiological heterogeneity within an ejaculate in terms of the development of cell subpopulations and enables the kinetic analysis of changes in living cell suspensions. The tests offer a promising strategy for evaluating fertility in domestic animals. The capability for volume regulation ensures that sperm recover from the tonic shocks experienced at ejaculation and during cryopreservation. Assessment of capacitationin vitroprovides valuable information on both the sperm’s ability to respond to fertilizing conditions and the sequence and rates of ongoing capacitation/destabilization processes. The monitoring of response to capacitating conditions in kinetic terms allows the sensitive and adequate detection of sperm populations expressing fertilization attributes and their ability to respond to external stimuli in a timely manner. However, subfertility is likely to be associated with a suboptimal response (i.e. too high or too low) rather than a minimal response.

Enhanced binding of sperm with superior volume regulation to oviductal epithelium

The plasma membrane is a key organelle with respect to sperm fertilizing ability. A sensitive way of testing plasma membrane functionality is to examine the sperm ability to moderate its swelling in response to hypo-osmotic stress (volume regulatory ability) using an electronic cell counter to assess cell volume changes. In this study of frozen-thawed bull sperm, we examined the relationship among sperm-oviductal epithelium binding capacity, osmotically induced swelling response, volume regulatory ability, and standard spermatologic parameters. Sperm cell volume distributions were measured under iso-osmotic conditions and after hypo-osmotic stress. The relative volume shift was calculated by comparing modal values of the cell volume distributions during transition from iso-osmotic to hypo-osmotic conditions. Significant correlations were found between volumetric parameters and sperm-oviduct binding capacity. Both the relative volume shift and regulative volume decrease correlated positively and significantly with the sperm-oviduct binding capacity. No significant correlations were found between sperm volumetric parameters and any of the standard sperm parameters with the exception of forward motility of Percoll-washed sperm. However, the use of multiple regression models improved the prediction level for binding capacity when motility parameters were combined with membrane integrity and volumetric parameters (R2 = .84). Spermatozoa of bulls with high nonreturn rates responded to hypotonicity as "perfect osmometers." Subfertile bulls had lower binding indices and deficiencies in volume recovery after hypotonic challenge, indicating that intact volume regulatory ability is a necessary prerequisite for binding to oviductal epithelium and is related to fertility. Volumetric parameters therefore could be used as tools in semen evaluation programs.

Binding of boar spermatozoa to oviductal epithelium in vitro in relation to sperm morphology and storage time

In vitro short-term storage of boar semen for up to 72 h before insemination negatively affects fertility, but this often remains undetected during semen quality assessment. One important sperm function is the ability to form the functional sperm reservoir in the oviduct. In the present study, we used the modified oviductal explant assay to study sperm binding to oviductal epithelium in vitro in diluted boar semen stored for 24 or 72 h. First, we determined the kinetics of in vitro sperm binding to oviductal epithelium in relation to co-incubation time of sperm and oviductal tissue pieces. Then, we studied how the binding of sperm to oviductal epithelium was affected by in vitro semen storage and by differences among individual boars. Sperm binding after different incubation times was significantly higher when semen was stored 24 h than after 72-h storage (P < 0.05), and peaked at 30–90 min of incubation. Sperm binding differed between boars (n = 44), and was negatively correlated to the percentage of sperm with cytoplasmic droplets (R = −0.51, P < 0.001). There were no significant changes in motility, acrosome integrity and propidium iodide stainability during the 72-h storage period. However, sperm-binding indices were significantly lower after 72 h in vitro storage than after 24-h storage in sperm from boars with normal semen quality (P < 0.05); in contrast, the binding capacity of sperm from boars with higher percentages of morphologically altered sperm remained at a low level. The sperm-binding capacity of sperm from four of the five boars with known subfertility was lower than the mean binding index minus one standard deviation of the boar population studied here. It is concluded that changes in the plasma membrane associated with in vitro ageing reduce the ability of stored boar sperm to bind to the oviductal epithelium. This study shows the potential of sperm–oviduct binding as a tool to assess both male fertility and changes in sperm function associated with in vitro ageing.

Importance of sperm-binding assays for fertility prognosis of porcine spermatozoa

There has been a considerable effort to establish correlations between the outcome of in vitro sperm-binding assays and the fertility achieved by individual males under conditions of commercial AI. During passage through the oviduct, a fertilizing spermatozoon has to bind to and interact with several targets. Generally, it is assumed that these interactions can be mimicked by in vitro binding assays. However, there is little evidence that assays based on zona binding, zona penetration, or IVF: (a) have been adequately validated; (b) provide data with a high degree of correlation to a boar of average fertility; (c) provide accurate predictions as to pregnancy rate and litter size from a given boar when used for commercial AI. This is due partly to the variability in measurements of pregnancy rate and litter size in a commercial setting and partly to the fact that sperm fertility is multifactorial. A recently developed in vitro test is based on the fact that spermatozoa bind in vivo to oviduct epithelium, creating a functional sperm reservoir, and that fertilization-competent spermatozoa are released in a time-dependent manner from these cells. Mating or insemination occurs usually hours before ovulation thus rendering such temporary sperm binding to the epithelial cells, a prerequisite for successful sperm-oocyte interaction. In vitro binding of porcine spermatozoa to explants derived from fresh oviduct epithelium may provide a useful test system to predict fertility, although detailed validation has not been published. The sperm-oviduct-binding assay tests for multifunctional characteristics of the plasma membrane and may be a valuable in vitro test to identify subfertile boars. We believe that boar subfertility might be indicated in vitro by reduced capacity of his spermatozoa to bind to oviductal cells and that this may provide information as to whether an adequate sperm reservoir will presumably be established in vivo from the sperm population that successfully has passed the barriers of the utero-tubal junction.

Requirement for an intact cytoskeleton for volume regulation in boar spermatozoa

Osmotically induced cell swelling triggers a chain of events leading to a net loss of major cell ions and water, resulting in cell volume recovery, a process known as regulatory volume decrease (RVD). In many cell types, there is an evidence that the cytoskeleton may play a role in the initial sensing and transduction of the signal of volume change. In this study, we tested the hypothesis that an intact microfilament and microtubule network is required for volume response and RVD in boar sperm before and after capacitation treatment and whether addition of cytochalasin D and colchicine to the capacitation medium would affect volumetric behaviour. Capacitation is a series of cellular and molecular alterations that enable the spermatozoon to fertilize an oocyte. Cell volume measurements of washed sperm suspensions were performed electronically in Hepes-buffered saline solutions of 300 and 180 mosmol/kg. After exposure to hypoosmotic conditions, boar sperm showed initial swelling (up to 150% of initial volume within 5 min), which was subsequently partially reversed (to about 120–130% after 20 min). Treatment with cytochalasin D led to reduced initial swelling (1 μmol/l) and loss of RVD in washed sperm (1–10 μmol/l) and at the beginning of incubation under capacitating conditions (5 μmol/l). Short treatment with 500 μmol/l colchicine affected the volume regulatory ability in sperm under capacitating conditions but not in washed sperm. No significant differences in cell volume response were observed after subsequent addition of cytochalasin D and colchicine to the suspensions of sperm incubated for 3 h under capacitating conditions. However, the incubation under capacitating conditions in the presence of cytochalasin D led to improved volume regulation at the end of the incubation period (23%). The microfilament network appears to be important for volume regulation in washed boar spermatozoa while intact microtubules do not seem to be necessary for osmotically induced RVD. The changes in cytoskeleton microfilament organization during capacitation, possibly affecting the osmotically induced volume response, appear to occur at the later stages of capacitation, whereas changes in microtubules, related to volume regulatory ability, may be programmed within the first stages of capacitation.

The effects of different insemination regimes on fertility in mares

This study investigated the effects of different artificial insemination (AI) regimes on the pregnancy rate in mares inseminated with either cooled or frozen-thawed semen. In essence, the influence of three different factors on fertility was examined; namely the number of inseminations per oestrus, the time interval between inseminations within an oestrus, and the proximity of insemination to ovulation. In the first experiment, 401 warmblood mares were inseminated one to three times in an oestrus with either cooled (500 x 10(6) progressively motile spermatozoa, stored at +5 degrees C for 2-4 h) or frozen-thawed (800 x 10(6) spermatozoa, of which > or =35% were progressively motile post-thaw) semen from fertile Hanoverian stallions, beginning -24, -12, 0, 12, 24 or 36 h after human chorionic gonadotrophin (hCG) administration. Mares were injected intravenously with 1500 IU hCG when they were in oestrus and had a pre-ovulatory follicle > or =40mm in diameter. Experiment 2 was a retrospective analysis of the breeding records of 2,637 mares inseminated in a total of 5,305 oestrous cycles during the 1999 breeding season. In Experiment 1, follicle development was monitored by transrectal ultrasonographic examination of the ovaries every 12 h until ovulation, and pregnancy detection was performed sonographically 16-18 days after ovulation. In Experiment 2, insemination data were analysed with respect to the number of live foals registered the following year. In Experiment 1, ovulation occurred within 48 h of hCG administration in 97.5% (391/401) of mares and the interval between hCG treatment and ovulation was significantly shorter in the second half of the breeding season (May-July) than in the first (March-April, P< or =0.05). Mares inseminated with cooled stallion semen once during an oestrus had pregnancy rates comparable to those attained in mares inseminated on two (48/85, 56.5%) or three (20/28, 71.4%) occasions at 24 h intervals, as long as insemination was performed between 24 h before and 12 h after ovulation (78/140, 55.7%). Similarly, a single frozen-thawed semen insemination between 12 h before (31/75, 41.3%) and 12 h after (24/48, 50%) ovulation produced similar pregnancy rates to those attained when mares were inseminated either two (31/62, 50%) or three (3/9, 33.3%) times at 24 h intervals. In the retrospective study (Experiment 2), mares inseminated with cooled semen only once per cycle had significantly lower per cycle foaling rates (507/1622, 31.2%) than mares inseminated two (791/1905, 41.5%), three (464/1064, 43.6%) or > or =4 times (314/714, 43.9%) in an oestrus (P< or =0.001). In addition, there was a tendency for per cycle foaling rates to increase when mares were inseminated daily (619/1374, 45.5%) rather than every other day (836/2004, 42.1%, P = 0.054) until ovulation. It is concluded that under conditions of frequent veterinary examination, a single insemination per cycle produces pregnancy rates as good as multiple insemination, as long as it is performed between 24 h before and 12 h after AI for cooled semen, or 12 h before and 12 h after AI for frozen-thawed semen. If frequent scanning is not possible, fertility appears to be optimised by repeating AI on a daily basis.

Assessing in vivo fertilizing capacity of liquid-preserved boar semen according to the 'Hanover gilt model'

The goal of this study was to determine the ability of the Hanover gilt model to assess in vivo fertilizing capacity of preserved sperm and to consider whether any modifications to this model were needed. This model evaluates the fertilizing capacity of semen based on the fertilization rate, the rate of normal embryos and the accessory sperm count of 3-5-day embryos. Its distinguishing characteristics are the use of one-time insemination of sperm in reduced numbers, of spontaneously ovulating gilts and of ovulation detection through ultrasound examination of ovaries. Reduced sperm numbers allow for an accurate evaluation of the fertilizing potential of different semen treatments, thereby avoiding the compensatory effect of doses calibrated to maximize fertility. The model's usefulness was assessed in a trial run designed to compare the fertilizing capacity of liquid boar semen diluted into two different extenders. The diluent, the boar and the backflow, had no significant effect on any of the parameters studied. Gilts inseminated less than 24 h before ovulation had a significantly higher (p < 0.01) fertilization rate and accessory sperm cell count (p < 0.05) than those inseminated more than 24 h before ovulation. Very good/good embryos from homogeneous litters (only very good/good embryos were present) had a significantly higher (p < 0.01) accessory sperm count than those from heterogeneous litters (at least one embryo was of a different quality and/or oocytes were present). Both very good/good and degenerated/retarded embryos from heterogeneous litters had low accessory sperm numbers. This suggests that accessory sperm count is significantly related to the quality of the litter, but not to the quality of the embryo within gilts. It can be concluded that the Hanover gilt model is sensitive enough to show fertility differences (in this study, those associated with in vivo ageing of semen), while using relatively few gilts and little time.

Kinetic characterization of the changes in protein tyrosine phosphorylation of membranes, cytosolic Ca2+ concentration and viability in boar sperm populations selected by binding to oviductal epithelial cells

On reaching the oviduct, spermatozoa are retained in the isthmic region of the oviduct until ovulation occurs. The essential steps of capacitation are co-ordinated in this region. In this study, a primary cell culture system of oviductal epithelial cells was established to investigate sperm binding to oviductal epithelium and modulation of sperm function during incubation under capacitating conditions in co-culture with oviductal epithelial cells. Epithelial cells were stripped from the oviducts of sows and cultivated for 5-7 days on Lab-Tek Chamber slides on Matrigel. The preparations on chamber slides and suspensions of control spermatozoa were incubated for 3 h in Tyrode's albumin lactate pyruvate (TALP) medium. At 3, 30, 60, 90 and 180 min the free-swimming spermatozoa were collected by washing, and membrane integrity, tyrosine phosphorylation patterns and [Ca(2+)](i) of bound, unbound and control spermatozoa were assessed with fluorescent probes (propidium iodide, Cy-3 and fluo-3-AM). The cells bound to oviductal epithelial cells showed reduced cytosolic Ca(2+) concentration, reduced and almost absent tyrosine phosphorylation of membrane proteins and higher viability at the time of the first sampling. Increases in Ca(2+) concentration and cell death occurred much more slowly during incubation in cells bound to oviductal epithelial cells compared with free-swimming spermatozoa, and no changes in tyrosine phosphorylation were observed. The preferential binding of viable, low-Ca(2+) cells with suppressed tyrosine phosphorylation and slower functional modulation of boar spermatozoa attached to oviductal epithelial cells might represent a mechanism for selecting functionally competent spermatozoa and prolonging their lifespan by delaying capacitation in the oviductal reservoir.

Selective sperm binding to pig oviductal epithelium in vitro

The sperm reservoir in the caudal isthmus of the oviduct of a number of species is created by binding of spermatozoa to oviductal epithelium. The sperm reservoir fulfills a number of functions such as control of sperm transport, maintenance of sperm viability and modulation of capacitation. The initial capacities of ejaculated and epididymal boar spermatozoa to bind to oviductal epithelium were investigated using a modified pig oviductal explant assay. The number of spermatozoa that bound to 0.01 mm(2) of explant surface was used as the parameter of binding capacity. Binding of spermatozoa to oviductal epithelial explants was dependent in a linear manner on the number of spermatozoa added (P < or = 0.05). No difference was found in initial sperm binding between isthmic and ampullar explants. There was no effect of the stage of the oestrous cycle or the reproductive status of the female donor. There was a significant effect (P < or = 0.05) of the individual boar on the binding index. The binding index correlated negatively with the percentage of spermatozoa with cytoplasmic droplets and the percentage of morphologically abnormal spermatozoa (P < or = 0.05). Epididymal spermatozoa showed significantly lower initial binding capability than did ejaculated spermatozoa from the same boars (P < or = 0.05); therefore, components of seminal plasma may play a role in the binding process. The individual differences revealed by this study and their relation to morphology and contact of spermatozoa with seminal fluid indicate a selective function of sperm-oviduct binding.

Selective sperm binding to pig oviductal epithelium in vitro

The sperm reservoir in the caudal isthmus of the oviduct of a number of species is created by binding of spermatozoa to oviductal epithelium. The sperm reservoir fulfills a number of functions such as control of sperm transport, maintenance of sperm viability and modulation of capacitation. The initial capacities of ejaculated and epididymal boar spermatozoa to bind to oviductal epithelium were investigated using a modified pig oviductal explant assay. The number of spermatozoa that bound to 0.01 mm(2) of explant surface was used as the parameter of binding capacity. Binding of spermatozoa to oviductal epithelial explants was dependent in a linear manner on the number of spermatozoa added (P < or = 0.05). No difference was found in initial sperm binding between isthmic and ampullar explants. There was no effect of the stage of the oestrous cycle or the reproductive status of the female donor. There was a significant effect (P < or = 0.05) of the individual boar on the binding index. The binding index correlated negatively with the percentage of spermatozoa with cytoplasmic droplets and the percentage of morphologically abnormal spermatozoa (P < or = 0.05). Epididymal spermatozoa showed significantly lower initial binding capability than did ejaculated spermatozoa from the same boars (P < or = 0.05); therefore, components of seminal plasma may play a role in the binding process. The individual differences revealed by this study and their relation to morphology and contact of spermatozoa with seminal fluid indicate a selective function of sperm-oviduct binding.

Detection of classical swine fever virus in semen of infected boars

During the Classical Swine Fever (CSF) epidemic in 1997 in the EU member states Germany, Italy, Spain and The Netherlands, boars in an artificial insemination (AI) centre were found to be infected with CSF virus. This raised a question of epidemiological importance which could not be answered immediately. Can CSF virus be shed by semen of infected boars and what conclusions concerning the risk of spreading CSF infection by semen can be drawn. Experimental studies were conducted to answer this question. Four young boars were infected with a CSF field virus isolate from Germany, which had been characterised in a previous animal experiment. Semen was collected at least every other day after infection. The semen was subjected to the standard diagnostic procedure for the detection of CSF virus and to semen quality assessment. The boars were euthanized at day 8, 12, 16 and 21 post infection, respectively. A post mortem examination was done and organ samples were taken from the CSF reference organs and genital organs for the detection of virus and antigen. The course of CSF infection of the boars was mild but detectable during the second week of infection. CSF virus could be isolated from semen of two animals during the pyrexic phase and from the epididymis but not from the testes. Since CSF virus shedding via semen could be proven, it was concluded that the disease may also be transmitted by artificial insemination. However analysis of semen in cell culture for the presence of CSF virus is not suitable as a routine method for CSF diagnosis.

Identification of embryo paternity using polymorphic DNA markers to assess fertilizing capacity of spermatozoa after heterospermic insemination in boars

Differences in sperm fertilizing capacity of males often remain undetected by routine semen parameters. Heterospermic insemination with equal numbers of spermatozoa from 2 males is an accurate method for assessing differences in fertility. Use of heterospermic insemination depends on a reliable, efficient assay to identify paternity of conceptuses or offspring. In this study, polymorphic DNA markers amplified by PCR were tested to determine paternity of Day 5 to 6 embryos. The fertilizing capacity of 2 boars (A and B) with similar semen parameters was compared after homospermic (n=14 gilts) and heterospermic (n=11 gilts) insemination. Single AI's were performed under suboptimal conditions using 1 x 10(9) spermatozoa at 12 to 24 h before ovulation to prompt differences in fertilization and to stimulate sperm competition. The fertilization rate and the number of accessory spermatozoa were determined in Day 5 to 6 embryos. Using 5 different polymorphic DNA markers, paternity could be determined in 95.8% of the embryos. Boar B sired significantly (P<0.05) more offspring than Boar A after insemination with pooled semen, and this was reflected by a significantly (P<0.05) higher number of accessory spermatozoa following homospermic insemination with semen from Boar B, although fertilization rates did not differ between the 2 boars after homospermic insemination. The results suggest that the viability of spermatozoa in the female reproductive tract contributes to differences in fertility rates of males with similar in vitro sperm quality parameters. The number of accessory spermatozoa is a more sensitive measure of boar fertility than the fertilization rate. Polymorphic DNA markers are suitable for verification of parentage even at a very early stage of embryonic development.

Studies on a local effect of boar seminal plasma on ovulation time in gilts

Previous studies showed that intrauterine infusion of seminal plasma at the onset of oestrus could advance ovulation in pigs, possibly to enhance the chances of fertilization by optimizing the chronological events of fertilization. This effect has been attributed to a local unilateral mechanism whereby infusion into a single uterine horn advances ovulation in the adjacent ovary. The present study was designed to elucidate possible mechanisms of local signal transduction. In a series of five experiments using 43 gilts, the ovarian response was investigated after infusion of seminal plasma at different sites of the female reproductive tract. The time of ovulation was detected sonographically at 4- or 2-h intervals. Single uterine horn infusion of 100 ml seminal plasma advanced ovulation on the ipsilateral ovary by 9.3 h (mean) compared with the contralateral ovary. Dissection of the ipsilateral isthmus abolished the unilateral seminal plasma effect. Unilateral infusion of 50 microliters or 1 ml seminal plasma or 50 microliters of the concentrated 1-10 kDa fraction in the lower isthmus was ineffective. Application of 5 ml seminal plasma into the tip of a ligated uterine horn lead to 3.6 h (mean) earlier ovulation on the adjacent ovary. In contrast, the infusion of 5 ml NaCl showed no effect. Application of 5 ml seminal plasma in the middle of the uterine horn between two ligatures was ineffective. It is concluded that, for the transduction of the local signal involved in the advancement of ovulation, contact of seminal plasma with the epithelium of the utero-tubal junction is essential.

Inheritance and genetic mapping of the Campus syndrome (CPS): a high-frequency tremor disease in pigs

A new progressive tremor disorder called Campus syndrome (CPS) was observed among the progeny of a normal boar of the Pietrain breed in Germany. Extensive backcross experiments indicate that CPS is inherited as an autosomal dominant trait, and the founder boar, Campus, is believed to be a gonadal mosaic. A linkage analysis of 57 animals mapped the CPS gene to a region on porcine chromosome 7 flanked by the markers SW1418 and SW352, which is homologous to a part of human chromosome (HSA) 14. Human dominant distal myopathy type 1 (MPD1) has been mapped to the homologous region of HSA14. As the myopathological findings in MDP1 show striking similarities to CPS, this porcine disorder may serve as an animal model for MPD1.

[In vitro assessment of semen for the prediction of fertility]

The prediction of fertility is a primary goal in the field of reproductive medicine. The aim of the present paper is to describe the value of conventional and modern sperm analysis systems considering the process of fertilization. The classical assessment of motility and morphology enables the rough estimation of semen quality in order to select ejaculates for the use in artificial insemination. Recent methods for sperm diagnosis, such as fluorescent marking for the detection of sperm plasma membrane integrity, the hypoosmotic swelling test, and computer assisted semen analysis allow for the evaluation of a large number of spermatozoa and the assessment of sperm dynamics under in vitro-fertilization conditions. The oocyte penetration test investigates the ability of spermatozoa for capacitation, hyperactivation and acrosome reaction in vitro. The amount of specific seminal plasma proteins is related to fertility and thereby provides an additional semen evaluation method. For the use of a given semen test the specific in vitro condition has to be considered. In addition, the evaluated criteria relevant for the process of fertilization need to be defined. The combination of selected semen tests gives a higher accuracy for the prediction of fertilizing capacity compared with a single test.

Effects of semen components on ovulation and fertilization

In pigs, transcervical infusion of seminal plasma at the onset of oestrus advances ovulation and thus improves the chance of gametes meeting during their full fertilizing competence. An animal model that allows single uterine horn infusion was used in combination with transcutaneous sonographic monitoring of ovaries. Preparative surgery involved the detachment of one uterine horn from the corpus, leaving the caudal end open to the peritoneal cavity but sealing the corpus wound. Transcervical infusion of 100 ml seminal plasma immediately after the detection of oestrus advanced ovulation by between 8 and 14 h on the ipsilateral ovary adjacent to the infused horn compared with the contralateral ovary. In addition, the seminal plasma infusion did not influence the LH profile compared with uterine infusion of PBS. This finding indicates that the effect is mediated by a local mechanism in the female genital tract. The advancement of ovulation depends on the time of infusion early in oestrus and is more pronounced in gilts exhibiting a long interval between the onset of oestrus and spontaneous ovulation compared with early ovulators. At 24 h after the detection of oestrus, seminal plasma was ineffective. Apparently, seminal plasma does not affect maturation and fertilizing competence of oocytes. The activity resides in a low molecular mass protein fraction and, to a far lesser extent, in seminal oestrogens. Further characterization of the active components may allow a practical application in AI.

Monoclonal antibodies against boar sperm zona pellucida-binding protein AWN-1. Characterization of a continuous antigenic determinant and immunolocalization of AWN epitopes in inseminated sows

Boar spermadhesin AWN-1 is a sperm surface-associated 14.7-kDa lectin and a major protein of porcine seminal plasma. AWN-1 binds to beta-galactosides and to porcine zona pellucida glycoproteins, suggesting that this protein might play a role in the primary binding of spermatozoa to the egg's external glycoprotein matrix. We have produced a collection of murine monoclonal antibodies against purified AWN-1. Five monoclonal antibodies recognized sequential antigenic determinants. All these epitopes were located at the C-terminal region of AWN-1 (residues 109-123) by competitive ELISA using overlapping synthetic peptides that cover the complete 133 amino acid sequence of the lectin. In a structural model of spermadhesin AWN-1, the polypeptide stretch 109-123 is fully solvent-exposed, providing a reasonable explanation for its high immunogenicity. In addition to epitope mapping, we have employed anti-AWN monoclonal antibodies for immunolocalization of the protein in the genital tract of inseminated sows. Clusters of AWN epitopes were occasionally found attached to the epithelium of the uterotubal junction and the adjacent lower isthmus. However, neither AWN-1 nor other seminal plasma proteins were found in the isthmic fluid collected 10-26 h after insemination. These results suggest that the whole amount of seminal plasma proteins are absorbed by the epithelium of the female genital tract, supporting the claim that removal of seminal plasma components from spermatozoa might be a major event in both in vitro and in vivo sperm capacitation.

[Cooling of boar spermatozoa prior to freezing and post thaw quality and evaluation of membrane state using chlortetracycline (CTC) staining]

The influence of an extended holding time at room temperature (+18 degrees C) before freezing on boar sperm quality was investigated. 17 ejaculates were collected from 5 different boars by separation in sperm rich and sperm poor fraction. The ejaculate were split, diluted 1+1 with Merck I-Medium, and submitted to three different treatments before freezing: 1. Sperm rich fraction, cooling to +20 degrees C for 1.5 h and subsequent cooling to +15 degrees C for 2.5 h; 2. Sperm rich fraction, cooling to +18 degrees C for 4 h and subsequent holding time at +18 degrees C for 16 h; 3. Whole ejaculate (sperm rich fraction plus seminal plasma), cooling to +18 degrees C for 4 h and subsequent holding time at +18 degrees C for 16 h. Subjectively assessed post thaw motility (SMOT), computer-measured motility (CMOT), and acrosome integrity (NAR), assessed by phase contrast microscopy were significantly (p < 0.05) higher after extended holding time (procedure 2 and 3) compared to short holding time (procedure 1). The exposure to seminal plasma during holding had no significant effect. Chlortetracyclin (CTC) staining of sperm membranes gave no reliable information in the presence of an EDTA-containing preservation medium, used routinely in the preservation process.

LH profile and advancement of ovulation after transcervical infusion of seminal plasma at different stages of oestrus in gilts

The influence of a transcervical infusion of seminal plasma on preovulatory LH profiles and the advancement of ovulation after seminal plasma infusion for different times during oestrus were investigated using the single uterine horn infusion technique (Mariensee model), in combination with transcutaneous sonographic monitoring of the ovaries. Preparative surgery in 23 German Landrace gilts comprised the detachment of the left uterine horn from the corpus, leaving the caudal end open to the peritoneal cavity but sealing the corpus wound. In six gilts fitted with a permanent jugular vein catheter the patent horns were administered a transcervical infusion of seminal plasma (n = 5 cycles) or PBS (n = 4 cycles) immediately after the detection of oestrus by a teaser boar. In addition, 17 non-catheterized gilts received infusions of seminal plasma either 0 h (n = 3 gilts), 16 h (n = 7 gilts) or 24 h (n = 7 gilts) after the detection of oestrus. Seminal plasma infusion at the onset of oestrus provoked ovulation in the ipsilateral ovary of the treated horn 8.5 +/- 0.9 h earlier than in the contralateral (control) ovary. Seminal plasma did not influence the LH profile compared with PBS (P > 0.05), but shortened the interval between the LH peak and ipsilateral ovulation to 23.4 +/- 4.0 h compared with 31.8 +/- 3.4 h in the contralateral ovulation (P < or = 0.01). Infusion 16 h after the onset of oestrus reduced the effect to 4.6 +/- 3.8 h with a wide range of 0-8 h (P < 0.01). The effect was more pronounced in gilts with long intervals between the onset of oestrus and contralateral ovulation compared with earlier ovulation on the control ovary. Seminal plasma infusion less than 16 h before contralateral ovulation and 24 h after the detection of oestrus had no effect. It is concluded that transcervical infusion of seminal plasma early in oestrus synchronizes the variable intervals between the onset of oestrus and ovulation in sows by a locally active mechanism.

Advanced ovulation in gilts by the intrauterine application of a low molecular mass pronase-sensitive fraction of boar seminal plasma

The shortening of the time interval between the onset of oestrus and ovulation in sows by the transcervical administration of seminal plasma was investigated in 23 German Landrace gilts, using the technique of single horn infusions (Mariensee model) in combination with the transcutaneous sonographic monitoring of ovaries. Preparative surgery comprised the detachment of the left uterine horn from the corpus, leaving the caudal end open to the peritoneal cavity but sealing the corpus wound. The left ovary was loosely tied to the ventral abdominal wall for better sonographic distinction. The animals were used in two to four consecutive cycles. After detection of oestrus by the teaser boar, the patent (right) horns were filled by transcervical infusion of 100 ml of a variety of test solutions. Ovulation was probed by transcutaneous sonography at intervals of 4 h thereafter. Native seminal plasma provoked ovulation in the ipsilateral ovary of the treated horn 10.7 h earlier than in the contralateral ovary. This effect was reduced to 7.3 h after charcoal treatment of seminal plasma; addition of 10 micrograms oestradiol restored the effect in full, while 10 micrograms of oestradiol in PBS shortened the time interval to only 3.3 h versus the control ovary. Little effect was seen with oestrone sulfate, none with prostaglandins in PBS or with PBS alone. The preliminary characterization of the nonsteroidal component of seminal plasma advancing ipsilateral ovulation after transcervical infusion suggests a proteinaceous nature. The activity resides in the 1-10 kDa fraction separated by ultrafiltration and is lost after treatment with pronase.

Effect of time of insemination relative to ovulation on fertility with liquid and frozen boar semen

Precise data on fertility results following peri- and postovulatory insemination in spontaneously ovulating gilts is lacking. Using transcutaneous sonography every 4 h during estrus as a tool for diagnosis of ovulation, the effects of different time intervals of insemination relative to ovulation were investigated with liquid semen (Experiment 1, n=76 gilts) and frozen semen (Experiment 2, n=80 gilts). In Experiment 3 (n=24 gilts) the number of Day-28 embryos related to the various intervals between insemination and ovulation was determined after the use of liquid semen. Using liquid semen the fertilization rates based on Day-2 to Day-5 embryos and the number of accessory spermatozoa decreased significantly in gilts inseminated with 2 x 10(9) spermatozoa per dosage in intervals of more than 12 h before or more than 4 h after ovulation. In the time interval 4 to 0 h before ovulation, comparable fertilization rates were obtained using frozen semen (88.1%) and liquid semen (92.5%). Fertilization rates and numbers of accessory spermatozoa decreased significantly when gilts were inseminated with frozen semen more than 4 h before or 0 to 4 h after the detection of ovulation. The percentage of Day-28 embryos was significantly higher following preovulatory insemination compared to inseminations 0 to 4 h and 4 to 8 h after ovulation. It is concluded that the optimal time of insemination using liquid semen is 12 to 0 h before ovulation, and 4 to 0 h before ovulation using frozen semen. The results stress the importance of further research on sperm transport and ovulation stimulating mechanisms, as well as studies on the time of ovulation relative to estrus-weaning intervals and estrus duration.