Effect of long-term storage in Safe Cell+ extender on boar sperm DNA integrity and other key sperm parameters

Abstract

BackgroundThere is some controversy about the extent of changes in different sperm cell features in stored boar semen, especially regarding the potential role of the DNA fragmentation assay for assessment of sperm fertilizing ability. The aim of this study was to assess the effect of time of storage and the dynamic changes in sperm cell characteristics in normospermic boar semen stored in long-term extender, in order to determine the susceptibility to damage of particular structures of spermatozoa during cooling and storage at 17 °C for 240 h post collection. The study included five ejaculates from each of seven boars of the Polish Large White breed (n = 35 ejaculates). The sperm characteristics were assessed using a flow cytometer and a computer assisted sperm analyzer on samples at 0, 48, 96, 168 and 240 h post collection.ResultsThe sperm chromatin structure assay (SCSA) showed a significant abrupt increase (P < 0.01) in the DNA fragmentation index (%DFI) after 48 h of semen storage with only subtle changes thereafter, not exceeding 5% on average after 240 h of storage. The use of a combination of SYBR-14/PI stains did not reveal any significant changes in the percentage of live sperm cells up to 168 h of semen storage. A significant (P < 0.01) decrease in the percentage of live spermatozoa with intact acrosomes was observed after prolonged semen storage (168 h). A significant and progressive decrease in sperm motility was recorded during the whole period of semen storage.ConclusionsStorage of boar semen extended in long-term diluent at 17 °C for 48 h initially induced a decrease in the integrity of sperm DNA. This suggests that the structure of boar sperm DNA is susceptible to damage, especially during semen extension and at the beginning of sperm storage. These findings support the opinion that the SCSA test has only a low potential for routine assessment of boar semen preserved in the liquid state and for assessment of sperm quality changes during 10 days of semen preservation. Remarkably, the integrity of acrosomes and plasma membranes remained nearly unchanged for 7 days.

Sperm DNA integrity in Landrace and Duroc boar semen and its relationship to litter size

“…Data from our initial work showed a small but significant increase in the DFI upon 96 hr liquid storage. This is in agreement with several previous studies reporting that in liquid preserved boar semen, spermatozoa show increased DNA fragmentation upon storage (Bielas, Nizanski, Partyka, Rzasa, & Mordak, ; Boe‐Hansen et al, ; Broekhuijse et al, ). In contrast to this, De Ambrogi et al () report that liquid storage of boar semen for up to 96 hr does not cause loss of DNA integrity.…”

“…Individual variation was, however, observed and a few samples showed DFI values above 10% and even up to values around 30%. The general low level of DNA fragmentation detected is in accordance with previous studies reporting mean DFI values from around 2%–4% in liquid stored boar semen (Bielas et al, ; Boe‐Hansen et al, ; Broekhuijse et al, ). However, these studies do also report individual variation between boars and ejaculates regarding the DNA fragmentation level on the day of collection and upon storage.…”

“…Thus in the current study, screening of DFI from samples stored for 48–96 hr was performed in order to mimic the status on the day of use in the herds. In the studies by Bielas et al () and Broekhuijse et al (), the greatest increase of DFI was observed between the day of collection and 24 hr’ storage. This supports our assumption that samples stored for 48–96 hr will adopt the “worst case” DFI value of the samples used for AI.…”

Preservation of boar semen: An update

“…There are commercial extenders (Beltsville TS [BTS], Modified Modena [MM] and MR‐A) that are effective for the extension and storage of boar semen, reaching on average 80% in gestation rates and 11 live births if the AI is done on the first day, whereas fertility is preserved if the number of sperm extended in BTS and MR‐A is doubled to 4 days (Johnson, Aalbers, & Grooten, ). The interaction of such factors as the ejaculate fraction, the extender, the boar and storage days significantly influences the quality of liquid‐stored sperm (Dziekońska, Świąder, et al, ), affecting mainly DNA integrity (Bielas, Niżański, Partyka, Rząsa, & Mordak, ); however, the main factors that affect cell functionality are the collection and storage temperature after dilution and the extender used (Johnson et al, ). The lipid composition of the sperm membrane in pigs is associated with cryotolerance (Yeste et al, ), since the cholesterol–phospholipid and protein–phospholipid ratios, 0.26 and 1.26 respectively (Parks & Lynch, ), increase sperm susceptibility to thermal shock, which occurs when the fresh semen cools off quickly from body temperature to 15°C (Johnson et al, ).…”

Protective influence of rosiglitazone against time‐dependent deterioration of boar spermatozoa preserved at 17°C

“…In the pig industry, artificial insemination is mostly done using boar semen preserved in the liquid state at 17°C; thus, effective long‐term preservation of functional boar spermatozoa remains an important target for the industry (Bielas, Niżański, Partyka, RząSa, & Mordak, ). After liquid preservation, boar spermatozoa show morpho‐functional changes that resemble the natural ageing process, while this can be relieved by proper storage conditions of diluted boar spermatozoa (Zakošek Pipan, Mrkun, Nemec Svete, & Zrimšek, ).…”