Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2006
Publication Date: 8/14/2006
Citation: Stewart, T., Gunsett, F., Welsh, C.S., Spiller, S.F., Purdy, P.H., Blackburn, H.D. 2006. Variation in sperm cell quality in cryopreserved boar semen. 8th World Congress of Genetics Applied in Livestock Production. 11(23):1-4.
Interpretive Summary: Two semen samples were collected from each of 163 boars representing four closed composite lines that are commercially available to US swine producers. Each sample was evaluated via computer assisted sperm analysis (CASA) and then prepared for and cryopreserved. After freezing, one 0.5 ml straw was thawed for the post-thaw CASA analysis. Variation in CASA traits associated with Stud (2 locations), Line (4), Collection (2 ejaculated samples) and Status (2 Fresh vs Cryopreserved) was evaluated. Significant sources of variation in sperm cell traits were associated with the stud where the boar was housed, semen status, and among boars. With few exceptions, variation among lines and between collections was not significant and when significance occurred there was no consistent ranking between lines. Regression of post-thawed sperm traits on fresh values of the same ejaculate were for the most part not significant as predictors. A notable difference was that fresh progressive motility is predictive of post-thaw progressive motility. Significant variation between studs and among boars emphasizes the need to use numerous sources of sires when sampling populations. These results also suggest that line differences for cryo-survival are a minor source of variation and therefore eliminate the need for line-specific cryopreservation protocols.
Technical Abstract: Quantifying the genetic variation between boars or their lines could be beneficial in selecting for increased reproductive performance and maintaining genetic diversity. Previous research has identified individual boar differences but no line differences have been identified at this time. To evaluate boar and line genetic differences, two semen samples were collected from each of 163 boars representing four closed composite lines that are commercially available to US swine producers. The boars were housed and managed at two different locations. Semen samples were evaluated for a number of sperm motion characteristics by computer assisted sperm analysis (CASA) prior to and after freezing. Variation in CASA traits associated with Stud (2 locations), Line (4), Collection (2 ejaculated samples) and Status (2 Fresh vs Cryopreserved) was evaluated. Highly significant sources of variation in sperm cell traits were associated with the stud where the boar was housed, semen status, and among boars. Line was not a significant factor in this analysis for most of the motion parameters; however, it was significant for beat cross frequency and cell elongation, but line rankings for these characteristics were not consistent. In regressing pre-freeze progressive motility on to post-thaw progressive motility, a significant regression coefficient of 0.15 was found indicating that collections with higher fresh progressive motility underwent cryopreservation better and had higher post-thaw progressive motilities. This result is encouraging given the relatively high heritability and genetic correlation, with fertility, for fresh progressive motility. The lack of significant differences between lines would imply that line-specific cryopreservation protocols are not needed.