VARIABILITA' NEL BOAR TAINT: ASSOCIAZIONI CON IL COMPORTAMENTO SESSUALE MASCHILE, CARATTERI QUALITATIVI DEL PROSCIUTTO CRUDO E REGIONI GENOMICHE

Boar taint (BT) is an off-odor affecting meat of boars after puberty. It is caused by the accumulation in fat of three main compounds: androstenone (AND), indole (IND), and skatole (SKA). Selecting pigs with reduced ability to accumulate BT compounds is a promising strategy to end surgical castration. However, the effects of a reduction in BT on other traits is unclear. Due to the presence of BT compounds in the testosterone pathway and other sexual steroids, the attempts at reducing BT might impair sexual behavior of pigs. Also, as sexual steroids are implicated in fat metabolism, such selection practices might impact carcass and meat quality. This is particularly relevant for pig lines intended for protected designation of origin dry-cured hams, where carcass and green ham features must meet product quality requirements. BT compound concentrations are difficult-to-measure phenotypes. For such traits, genomic selection strategies could minimize the number of individual phenotypes required to predict the genetic merit of breeding candidates. Hence, the aims of the thesis were to: 1) estimate the association between BT compound concentration and male sexual behavior; 2) compare the accuracy of pedigree-based and genomic selection for BT compounds; 3) identify the genomic regions associated with BT; 4) estimate the genetic correlations between BT traits measured in purebred pigs and carcass and green ham quality traits measured in crossbreds. BT compound concentrations were quantified by HPLC in biopsies of adipose tissue of 1115 boars of a purebred line selected for ham quality. 1075 animals had also available genotypes at 29844 SNPs and 391 animals had the sexual behavior evaluation during the training with the dummy sow. The association between BT compound level in backfat and libido was investigated by proportional-odds cumulative logistic models. Traditional and SNP-based breeding values for BT traits were estimated using pedigree-based BLUP (PBLUP) and genomic BLUP (GBLUP), respectively. Genomic regions associated with BT traits were identified through a GBLUP genome-wide association study (GWAS), followed by a post-GWAS analysis to identify candidate genes nearby the most influential genome-wide SNP windows. The genetic correlations between BT compound levels and carcass and ham quality traits were estimated using the purebred boars with BT records and production and ham quality traits collected in 26577 crossbred heavy pigs. Genetic correlations were estimated in bivariate Bayesian analyses including one BT trait and one production or ham quality trait at a time. Results indicated that BT compound concentrations were weakly associated with libido, even though the probability of observing good libido scores increased with high levels of AND, intermediate or low levels of SKA, and intermediate to high levels of IND. The accuracies of GBLUP and PBLUP were significantly different for a AND (0.58 and 0.36, respectively), and comparable for indole and SKA (~0.43 and ~0.47, respectively). Several SNP windows, each explaining a small percentage of the variance of BT compound concentrations, were identified, as well as different candidate genes associated with BT, reproduction traits and fat metabolism. The large number of genes related to fat metabolism might be explained by the relationship between sexual steroid levels and fat deposition and be the result of the pig line investigated. Heritability of AND, SKA and IND was 0.41, 0.49 and 0.37, respectively. Correlations between BT compounds and iodine number ranged from -0.07 (for AND) to -0.64 (for SKA), whereas those with PUFA ranged from -0.13 (for IND) to -0.33 (for SKA) suggesting that reducing BT could decrease ham fat thickness and increase PUFA, with potential negative impacts on product quality. Overall, the findings of this study highlight the importance of understanding the complex relationships between BT compound levels and other traits of interest.