Concentrations of fat and plasma 5alpha-androstenone and plasma testosterone in boars selected for rate of body weight gain and thickness of back fat during growth, sexual maturation and after mating.

The levels of 5alpha-androstenone and testosterone in peripheral plasma and 5alpha-androstenone in fat collected from 18 boars selected according to thickness of back fat and rate of gain were evaluated. Sampling was started when the animals were about 100 days of age and samples were collected every 14 days until the boars were about 240 days old. The steroid profiles varied considerably between boars, although an increase in steroid levels was found in most animals with the onset of adolescence. The regression line for the level of 5alpha-androstenone in fat and the age of the animals in days was found to be y = 0.02x-1-31. High coefficients of correlation were found between the concentration of 5alpha-androstenone in peripheral plasma and fat (r = 0-78) and between levels of 5alpha-androstenone and testosterone in peripheral plasma (r = 0-64). Levels of 5alpha-androstenone in peripheral plasma above about 15 ng/ml were usually accompanied by a heavy accumulation of 5alpha-androstenone in adipose tissue. The use of four of the boars for mating resulted in increased steroid levels in peripheral plasma and fat. Significantly higher levels of 5alpha-androstenone and testosterone were found in the peripheral plasma of boars selected for fatness and a low rate of gain than in boars selected for low back-fat thickness and a high rate of gain.