Genetic Components and Relationships of Boar Semen Quality and Fertility Traits

Boars that do not produce semen meeting quality thresholds affect producers’ revenue stream. As producers are required to utilize extra and genetically less superior boars to compensate for poor quality, this precipitates reduced genetic gain and profitability of offspring. Female fertility has been a focus of selection for years with measurable improvements transpiring. Though the economic impact of semen quality on production has been shown, very little has been done to improve male fertility. Therefore, the overall objective of this dissertation was a detailed genetic analysis of sperm quality and boar fertility traits. The pampiniform plexus (PP) vessels of boars were ultrasonically measured and assessed for varicocele, a known fertility disorder in other species. The heritability of PP vessel size and varicocele were estimated and PP vessel size was found to be highly heritable, whereas varicocele was moderately heritable. The relationship between varicocele and semen quality was assessed with the presence of varicocele having a significant effect on sperm concentration, distal droplet percentage (DIST), and trended toward significance for sperm head area. The heritability and repeatability of sperm quality traits were estimated. The genetic relationship among these traits were also estimated as well as the influence these sperm quality traits had on total number born (TNB). Heritability estimates ranged from 0.08 to 0.24 and repeatability estimates ranged from 0.21 to 0.62. The phenotypic and genetic correlations between morphological defects and sperm motility traits indicated a negative relationship. Total sperm motility had a significant positive effect on TNB, whereas DIST, proximal droplet percentage, bent tail percentage, and distal midpiece reflux had a significant negative effected on TNB. Lastly, the relationship between total motile sperm cells (TMS) and traits typically included in a terminal sire index (TSI) was assessed. Strong positive genetic relationships existed between TMS and both feed efficiency ratio and backfat, while strong negative genetic relationships existed between TMS and loin depth as well as lean yield percentage. The rank correlation between TMS estimated breeding values and boar ranking by TSI resulted in a correlation of 0, suggesting TMS is not being selected for or against by current selection methods