Patterns of plasma sexual steroids in Duroc and Pietrain crossbred male pigs in organic farming and prediction of boar taint risk according to slaughter weight.

Boar taint risk in pork highly depends on fat tissue concentrations of androstenone and skatole, and indole to a lower extent. During pubertal development, androstenone is increasingly produced by testes and accumulates in fat tissues. Skatole and indole are produced and absorbed along in the colon and also accumulate in fat tissues. Skatole and indole are catabolised in the liver, but sexual steroids (including androstenone) inhibit their liver degradation. Therefore, slaughtering pigs before the pubertal peak of steroid production should reduce boar taint risk and thus make it possible to raise male pigs without inflicting detrimental castration. In the present experiment, non-castrated male pigs from two genotypes differing in their propensity to accumulate androstenone and skatole in backfat were compared: Large White × Duroc (D; n = 47) and Large White × Pietrain crossbreds (P; n = 34). Blood samples were drawn from the jugular vein two times during growth (at around 85 kg BW and 133 days of age, and around 105 kg BW and 153 days of age) and the day before slaughter (around 125 kg BW and 174 days of age). Plasma testosterone and 17β-oestradiol, whose concentrations increase during sexual development, were measured in all samples and correlated with backfat concentrations of androstenone, skatole and indole measured at slaughter. Plasma concentrations of both hormones increased (P < 0.05) from the first to the second, and from the second to the third sampling stage (P < 0.05). Plasma testosterone concentration did not differ between genotypes (P > 0.1) whereas plasma 17β-oestradiol was more than twice higher in D than in P pigs (P < 0.001) regardless of the age. Plasma 17β-oestradiol concentration measured the day before slaughter was highly correlated with backfat androstenone (r = 0.91, P < 0.001). Estimating backfat androstenone concentration from that of plasma 17β-oestradiol allowed to predict that reducing slaughter BW from more than 125 kg to less than 110 kg would reduce the percentage of carcasses with androstenone concentration above 1.7 µg/g liquid fat (severe threshold limit for boar taint) from 42 to 29% in D pigs and from 10 to 0% in P pigs, and with androstenone concentration above 3 µg/g (less severe limit for boar taint) from 19 to 7% in D pigs, whereas none of the P pigs would be above this limit regardless of the age. In conclusion, pig genotype and reducing slaughter BW (and age) are strong levers to avoid boar taint.