Sperm chromatin structural integrity in normospermic boars is not related to semen storage and fertility after routine AI

Standard semen parameters are limited in their capacity to distinguish subfertile boars and to assess storage influences on liquid preserved boar semen. The evaluation of sperm chromatin structural integrity could have potential as a diagnostic tool in AI practice. This study assessed whether the determination of sperm DNA integrity adds a useful diagnostic tool for selection of boar ejaculates in routine AI procedure and assessment of storage effects in diluted semen. Special emphasis was laid on the standard spermatological characterization of semen samples in parallel with the determination of the DNA fragmentation index (DFI) through the sperm chromatin structure assay (SCSA). Six hundred ninety two (692) ejaculates from 79 Pietrain boars in an AI center were analyzed for motility, morphology and DFI over a period of 24 weeks. 95.5% of the semen samples had a DFI < 5% with low distribution of variation for DFI due to boar and ejaculate (< 5%). 61.3% of ejaculates with DFI > 5% showed values below thresholds for sperm motility or morphology. Based on field data from 13,239 inseminations, fertility of boars with temporarily elevated DFI was not impaired (P > 0.05). 24 randomly selected diluted semen samples did not show a significant increase of DFI during 168 h storage (P > 0.05). In a further experiment, 42 diluted semen samples from 14 normospermic boars were assessed for motility, membrane integrity (PI, FITC-PNA) and SCSA parameters. Three single ejaculates showed an increase of DFI at 120 and 168 h storage time. This was accompanied by a pronounced loss of both motility and membrane integrity. In conclusion, the evaluation of sperm chromatin structural integrity by the SCSA has only limited value for identifying sperm deficiencies in normospermic fresh or stored boar semen. Temporarily elevated DFIs seem not to be indicative of subfertility in normospermic boars. Crown Copyright (C) 2011 Published by Elsevier Inc. All rights reserved.