Effects of age and live weight on fat 5 alpha-androstenone levels in young boars fed two planes of nutrition.

The aim of the present experiment was to determine whether age, live weight, or a combination of both, was the most important factor influencing fat 5 alpha-androstenone levels in male pigs. Three groups of 50 boars each were fed either on a liberal plane of nutrition (CTRL group) or were restricted (SW and SA groups). Fat 5 alpha-androstenone was measured three times in each pig (on biopsies at two different times and at slaughter) at either the same live weight (SW) or at the same age (SA) as CTRL boars. In addition, the genital tract was dissected at slaughter. SW boars (aged 169 days) exhibited higher fat 5 alpha-androstenone levels than CTRL boars (aged 139 days) when the first biopsy was taken at 80 kg of live weight (1.2 vs 0.8 microgram/g; P less than 0.05). By the time of the second biopsy (100 kg of live weight) and at slaughter (125 kg) there was no significant difference between the SW and CTRL groups, although the SW were 43-55 days older than the CTRL. At all three measurement times, fat 5 alpha-androstenone was lower in SA than in CTRL boars which were 21-36 kg heavier (0.5 vs 0.8 micrograms/g at 139 days; 0.9 vs 1.3 micrograms/g at 160 days; 1.2 vs 2.0 micrograms/g at 185 days; P less than 0.001). Partial correlations between fat 5 alpha-androstenone and age were significant at the first biopsy, whereas partial correlations with live weight were significant at all three times of measurement. In SA boars weighing 90 kg there was a significant correlation between fat 5 alpha-androstenone and all the developmental traits of the genital tract. In SW and CTRL pigs weighing 125 kg, fat 5 alpha-androstenone was significantly correlated with accessory sex gland development but not with testis or epididymis weight. From the present data it is concluded that both age and live weight had a significant effect on fat 5 alpha-androstenone levels in young, light boars. In older, heavier boars, age had no effect per se but live weight still had a significant influence on 5 alpha-androstenone concentrations. In boars weighing 90 kg, fat 5 alpha-androstenone level depended on sexual maturity. When the animals were sexually mature at 125 kg of live weight, 5 alpha-androstenone level depended on the individual's potentiality for steroid production, which is probably under genetic control.