New approach to assess sperm DNA fragmentation dynamics: Fine-tuning mathematical models

Abstract

BackgroundSperm DNA fragmentation (sDF) has been proved to be an important parameter in order to predict in vitro the potential fertility of a semen sample. Colloid centrifugation could be a suitable technique to select those donkey sperm more resistant to DNA fragmentation after thawing. Previous studies have shown that to elucidate the latent damage of the DNA molecule, sDF should be assessed dynamically, where the rate of fragmentation between treatments indicates how resistant the DNA is to iatrogenic damage. The rate of fragmentation is calculated using the slope of a linear regression equation. However, it has not been studied if sDF dynamics fit this model. The objectives of this study were to evaluate the effect of different after-thawing centrifugation protocols on sperm DNA fragmentation and elucidate the most accurate mathematical model (linear regression, exponential or polynomial) for DNA fragmentation over time in frozen-thawed donkey semen.ResultsAfter submitting post-thaw semen samples to no centrifugation (UDC), sperm washing (SW) or single layer centrifugation (SLC) protocols, sDF values after 6 h of incubation were significantly lower in SLC samples than in SW or UDC. Coefficient of determination (R2) values were significantly higher for a second order polynomial model than for linear or exponential. The highest values for acceleration of fragmentation (aSDF) were obtained for SW, followed by SLC and UDC.ConclusionSLC after thawing seems to preserve longer DNA longevity in comparison to UDC and SW. Moreover, the fine-tuning of models has shown that sDF dynamics in frozen-thawed donkey semen fit a second order polynomial model, which implies that fragmentation rate is not constant and fragmentation acceleration must be taken into account to elucidate hidden damage in the DNA molecule.

Comparison of different mathematical models to assess seasonal variations in the longevity of DNA integrity of cooled‐stored stallion sperm

“…Sperm DNA fragmentation analysis was performed for each sample after 0, 6 and 24 hr of cooled storage. SDF values were then analysed using three mathematical regression models for dynamic assessment: linear, exponential and second order polynomial, as previously described (Ortiz et al, ). In order to compare which model was the better fit for SDF, the coefficient of determination ( R 2 ) was calculated.…”

“…It is also well known that stallion semen cooling affects routine sperm quality parameters and pregnancy rates (Brinkerhoff et al, ; Foster et al, ; Heckenbichler, Deichsel, Peters, & Aurich, ; Henderson, Capewell, & Johnson, ; Kiser et al, ; Love et al, ; Urbano et al, ), mostly attributable to the relatively short longevity of cooled‐stored semen of approximately 24–48 hr. Other studies have shown that semen cooling increases SDF values after 48 hr of storage (Blottner et al, ; Fraser, Strzezek, & Kordan, ; Gil et al, ; Linfor & Meyers, ; Love & Kenney, ; Love et al, ; Ortiz et al, ).…”

“…Despite the equine has been well established as a long‐day seasonal breeder (Chemineau et al, ; Hoffmann & Landeck, ; Janett, Thun, Niederer, Burger, & Hassig, ; Jasko, Lein, & Foote, ; Magistrini, Chanteloube, & Palmer, ; Pickett, Faulkner, Seidel, Berndtson, & Voss, ; Wach‐Gygax et al, ), there are remarkably only a few studies that have exanimated this phenomenon on semen quality, with these studies typically confirming better semen quality in the spring (Blottner, Warnke, Tuchscherer, Heinen, & Torner, ; Chemineau et al, ; Wach‐Gygax et al, ). While there is still debate in the literature about the specific impact of season on each parameter, there is, nevertheless, overall agreement that season (photoperiod) does influence sperm quality (Chemineau et al, ; Hoffmann & Landeck, ), including that of SDF (Blottner et al, ; Chemineau et al, ; Morte et al, ; Ortiz et al, ; Wach‐Gygax et al, ).…”

“…This dynamic assessment also allows the calculation of a rate of SDF (rSDF) which can then be fine‐tuned using a linear regression model (Cortes‐Gutierrez et al, ; Lopez‐Fernandez et al, ; Urbano et al, ). These linear models suppose that the velocity of rSDF is constant, an assumption that some authors claim to be incorrect (Ferreira et al, ; Love, Thompson, Lowry, & Varner, ; Ortiz et al, ). More recently, a new approach to the analysis of rSDF that involves the use of and second order polynomial mathematical models has been established (Ortiz et al, ).…”

“…These linear models suppose that the velocity of rSDF is constant, an assumption that some authors claim to be incorrect (Ferreira et al, ; Love, Thompson, Lowry, & Varner, ; Ortiz et al, ). More recently, a new approach to the analysis of rSDF that involves the use of and second order polynomial mathematical models has been established (Ortiz et al, ). These two models imply that the velocity of DNA fragmentation is not constant over time (de la Horra Navarro, ).…”