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

The sperm chromatin structure assay is a method for assessment of sperm DNA fragmentation, a parameter reported to be negatively related to field fertility in several mammal species. This method calculates a DNA fragmentation index (DFI) whose high values indicate abnormal chromatin structure. In this study, running from March 2010 until June 2017, the aim was to assess sperm DFI in stored liquid extended semen from two different pig breeds, Norwegian Landrace (NL; n = 693) and Norwegian Duroc (ND; n = 655), and to evaluate the influence on total number of piglets born (TNB). There was a significantly higher median DFI (p < 0.0001) in ejaculates from the 478 ND boars compared to the 452 NL boars. Data from 19,496 NL litters and 3,877 ND litters of the same boars were retrieved. For either breed, sow herd (p < 0.0001), parity (p < 0.05) and DFI (p < 0.05) showed significant effects on TNB. The DFI was negatively correlated to TNB in both breeds. The boars with the 5% lowest TNB had a least square means DFI of 3.05% and 2.24% in NL and ND, respectively, compared to 1.67% and 1.23% for the boars with the 5% highest TNB (p < 0.01). The DFI and the motility of the same semen samples were negatively correlated (p < 0.0001), and the high and low TNB groups showed significant differences in motility. However, this difference could not be used for practical prediction of TNB group (92.1% vs. 89.7%; p = 0.0038 and 92.3% vs. 89.5%; p = 0.018; NL and ND, respectively). In conclusion, our results indicate that sperm DNA integrity in semen with good motility and morphology may be an additional prediction parameter for fertility in pigs.