Enhanced prediction of frozen boar sperm fertility by assessing classical and novel traits collectively

Abstract Text:

Cryopreserved semen is seldom used for commercial porcine artificial insemination (AI) despite the many advantages of frozen sperm.  Compared to fresh semen, the fertility of frozen-thawed boar sperm is more variable and usually lower.  Predicting the fertility of individual ejaculates to select higher quality semen for AI would increase success.  Our objective was to test novel and classical laboratory analyses to identify characteristics of cryopreserved sperm that collectively predict boar fertility.  Single ejaculates of sperm from 14 boars of several breeds were collected and frozen.  Traditional post-thaw analyses of motility, viability and acrosome integrity were evaluated at 0, 30 and 60 min post-thaw.  IVF, cleavage and blastocyst development were also determined.  Finally, a sperm-oviduct binding assay and a competitive zona binding assay were applied to calculate sperm adhesion to these two matrices.  Fertility of the same ejaculates subjected to lab assays was determined for each boar by AI of mature gilts using 4.0 x 10⁹ total sperm from one boar at 24 h and a second boar at 36 h after the onset of estrus.  Boar insemination order was reversed in consecutive replicates.  Reproductive tracts were harvested at 32 d after AI and fetal paternity was identified using DNA microsatellite markers.  Fertility was defined as (1) the mean percentage of the litter sired and (2) the mean number of piglets sired in each litter.  Means of each lab evaluation were individually modeled by boar and those values were applied to stepwise multiple linear regression analyses to determine which sperm traits could collectively estimate fertility in the simplest model.  The regression model to predict the percent of litter sired by boar was highly effective (p < 0.001, r² = 0.87) and included 5 traits; acrosome compromised sperm, percent live sperm, percent total motility and the number of zona-bound sperm.  A second model to predict the number of piglets sired by boar was also effective (p < 0.05, r² = 0.57).  These models indicate that the fertility of cryopreserved boar sperm can be predicted effectively by including traditional and novel laboratory assays that assess multiple functions of sperm.  Inclusion of novel functional traits of sperm with classical traits was a useful approach to enhance fertility prediction and more accurately identify ejaculates of low fertility.

Agriculture and Food Research Initiative Competitive Grant no. 2010-85112-20620 from the USDA National Institute of Food and Agriculture.

Keywords: boar, frozen, sperm