Physiological and Biochemical Factors Responsible for Boar Taint

Chen, G. 2007. Physiological and biochemical factors responsible for boar taint. Doctoral thesis. ISSN: 1652-6880. ISBN: 978-91-85913-09-1 We used entire male pigs to: 1) compare different methods to analyse boar taint compounds; 2) evaluate the effects of raw potato starch (RPS), high amylose barley cultivar (Karmosé), sire selection and live weight on the levels of boar taint compounds; 3) investigate the relationship between indolic compounds and testicular steroids by using an hCG injection model; 4) evaluate the effect of incubation with steroids and indolic compounds on CYP2A6 protein expression in hepatocytes; 5) investigate the relationship between testicular steroids and gene expression of hydroxysteroid dehydrogenases (3βHSD and 17βHSD) in entire male and castrated male pigs. The results showed that HPLC method and GC-MS method for fat androstenone analyses were comparable. HPLC and ELISA methods for fat androstenone analyses were well correlated (r = 0.90), but the result from the ELISA method was overestimated. HPLC and colorimetric method for fat skatole analyses were well correlated (r = 0.94) even though the two methods used different sample matrix. Plasma androstenone results determined by ELISA method with and without sample extraction were moderately correlated (r = 0.70). The results from analyses without sample extraction were 4 times higher than the results from analyses with sample extraction. Feeding RPS reduced fat skatole levels, but not fat androstenone and indole levels of entire male pigs. High amylose barley did not influence any of the boar taint compounds analyzed in fat (skatole, androstenone and indole). Androstenone levels in fat were higher at live weight 115 kg than at 90 kg, whereas fat skatole and indole levels did not differ between the two live weights. Sire selection based on plasma skatole levels significantly influenced skatole, androstenone and indole levels in fat in the progenies. Indole levels in plasma and in fat were significantly increased after hCG injection, and skatole levels in fat tended to be increased. This increase was associated with the abrupt increase of testicular steroids by hCG injection. An in vitro study showed that both skatole and indole at low concentrations (0-100 nM) induced cytochrome P450 2A6 (CYP2A6) protein expression in cultured hepatocytes, with a more prominent effect for indole. Androstenone at low concentration (0-100 nM) inhibited CYP2A6 protein expression. Testosterone and estrone sulfate (E1S) did not affect CYP2A6 protein expression. High fat androstenone levels were negatively associated with low 3βHSD gene expression in entire male pigs. Fat androstenone levels were also negatively associated with 17βHSD gene expression in liver but not in testis. The correlation between hepatic 17βHSD gene expression and plasma E1S was high. In addition, gene expression of 3βHSD and 17βHSD was highly correlated. Gene expressions of 3βHSD and 17βHSD in liver were much higher in surgically castrated and immunocastrated pigs than in entire male pigs with high fat androstenone levels. The gene expression of 3βHSD was generally much higher than 17βHSD both in liver and in testis.