Effect of 19-norandrostenololylaurate on serum testosterone concentration, libido, and closure of distal radial growth plate in colts.

The long-term effect of anabolic steroid was investigated in 3 experiments. In experiment I, 500 mg of 19-norandrostenololylaurate was given to 5 colts and a dose of 100 mg to another 5 colts every 3rd week. Six colts served as untreated controls. The animals were 12-16 months old at the start, and 24 months at the end of treatment. In experiment II, a dose of 1 mg/kg was given every 3rd week to 4 colts and 0.3 mg/kg every week to another 4 colts. Six colts served as controls. The colts were treated from 7 months to 12 months of age. In experiment III, 1 mg/kg of steroid was given every 3rd week to 3 foals between 3 and 8 months of age. Three foals were used as controls. Libido and hCG-induced serum testosterone concentrations were studied after the cessation of treatments, up to 3 or 4 years of age. Closure of the right distal radial growth plate was determined between 21 and 36 months of age. Treated colts had lower testosterone levels 4.5 months after cessation of treatment in experiment I (p < 0.001) and experiment II (p < 0.05) when compared with the corresponding control groups. Two years after treatments in experiment I, hCG-induced testosterone levels were higher in treated colts than in untreated controls, but the difference was not statistically significant. The treatments had no effect on libido. The anabolic steroid treatment did not cause premature closure of epiphyseal growth plates in any of the experiments, but closure appeared to be delayed. It was concluded that anabolic steroids have long term effects on reproduction. Their influence on serum testosterone can last for years after cessation of treatment, and they can delay the closure of growth plates which can cause increased susceptibility to cartilage injury during exercise.