Identification of genetic and transcriptomic factors potentially related to sperm cryotolerance in swine

Sperm cryopreservation offers great managerial advantages for animal breeding, but it is uncommon in swine, partly because sperm cryotolerance varies substantially among samples. The biological basis of sperm cryotolerance remains poorly understood, which limits the development of optimal cryopreservation strategies. The aim of this exploratory study was to identify candidate genetic and transcriptomic factors that may affect sperm cryotolerance in pigs. We measured the percentages of viable sperm and abnormal acrosomes in frozen-thawed samples after five and 90 min of incubation at 37°C. Then, we derived ratios of these parameters describing resistance to freezing, thawing, or both, and clustered samples with distinct cryotolerance using four approaches. An exploratory small-scale genome-wide association study and genomic partitioning of additive variance were performed on 99 boars, and sperm's RNA-Seq analyses were conducted on 20 of these animals. No SNP reached genome-wide significance. However, using chromosome-wise thresholds for correction for multiple testing, we identified a candidate genomic region on chromosome 12 associated with resistance to both freezing and thawing, as well as multiple genomic regions explaining more than 1% of the additive variance for six cryotolerance parameters. Several ratios correlated with the RNA levels of 11 genes. Differential expression analyses identified nine genes linked to cryotolerance across clustering approaches, some related to oxidative stress, mitochondrial function, apoptosis, and calcium signalling.