97 DIFFERENCES IN SPERM CHROMATIN STRUCTURE AMONG GOOD AND BAD BOAR SPERM FREEZERS

Abstract

Inter- and intra-boar differences in sperm freezability are observed independent of the sperm quality before freezing, the breed, or the genetic line. This study aimed to determine whether boars with different post-thaw sperm quality also show differences in sperm DNA integrity. Sperm-rich fractions (3 to 10 ejaculates per boar) from 19 fertile mature boars were extended in Beltsville thawing solution (BTS) and cooled to 17°C for 16 h. Then, samples were centrifuged at 2400g for 3 min, extended in freezing extender (lactose/egg yolk/glycerol/Equex STM; Nova Chemical Sales, Inc., Scituate, MA, USA) to a final concentration of 1 × 10⁹ spermatozoa/mL, dispensed into 0.5 mL straws, and frozen in a programmable cell freezer at a rate of -20°C min. Thawing was carried out in a water bath at 37°C for 20 s. Frozen-thawed spermatozoa were evaluated for progressive sperm motility (PSM) using a computer-assisted sperm analysis (CASA) system, and sperm viability (PMI) using flow cytometry. All data generated were used for a multivariate pattern analysis (PATN; CSIRO, Canberra, Australia) which objectively classified all boars into two groups, categorized as good (n = 10; >60% PSM and PMI) or bad (n = 9; <40% PSM and PMI) based on their sperm freezability. Post-thaw sperm quality was consistent for different ejaculates within boars (P < 0.05). The DNA-integrity of frozen-thawed spermatozoa was evaluated according to the sperm chromatin structure assay (SCSA; Evenson et al. 1980 Science 210, 1131-1133). All SCSA variables (X mean, DNA fragmentation index (DFI), and the standard deviation of the DFI), were significantly higher for bad freezers (P < 0.001). The percentage of spermatozoa with abnormal chromatin structure ranged from 1.06 to 3.42% for good and 3.06 to 6.04% for bad freezers. Although these differences exist between good and bad sperm freezers, and can only to some extent be the product of cryopreservation, the levels of affected spermatozoa can not explain the differences on post-thaw sperm survival seen in the two categories of sires.

This work was supported by CICYT, AGL05-0471 (Spain), SLF and Formas (Sweden).