title: New approach to assess sperm DNA fragmentation dynamics: Fine-tuning mathematical models.
abstract: BACKGROUND
  Sperm 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.
  
  
  RESULTS
  After 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.
  
  
  CONCLUSIONS
  SLC 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.
authors.affiliation: Veterinary Reproduction Group, Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, University of Cordoba, 14071 Cordoba, Spain.
authors.forename: Isabel
authors.identifier: 0000-0002-2479-498X
authors.initials: I
authors.lastname: Ortiz
authors.affiliation: Veterinary Reproduction Group, Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, University of Cordoba, 14071 Cordoba, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Dorado
authors.affiliation: Department of Clinical Sciences, Division of Reproduction, Swedish University of Agricultural Sciences, Box 7054, SE-75007 Uppsala, Sweden.
authors.forename: Jane
authors.initials: J
authors.lastname: Morrell
authors.affiliation: Department of Biology, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Jaime
authors.initials: J
authors.lastname: Gosálvez
authors.affiliation: Department of Reproduction, Centro Militar de Cría Caballar (FESCCR-Ministry of Defense), 05005 Ávila, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Crespo
authors.affiliation: Department of Chemistry and Physics of Materials, University of Salzburg, Hellbrunner Straße 34/III, A-5020 Salzburg, Austria.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Jiménez
authors.affiliation: Veterinary Reproduction Group, Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, University of Cordoba, 14071 Cordoba, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Hidalgo
keywords: Colloid centrifugation; Dynamics; Fine-tuning; Mathematical models; Sperm DNA fragmentation