Testicular maturation in prepubertal New Zealand white rabbits.

Testicular maturation was assessed in age-matched, sexually immature (13-17-week-old) New Zealand white rabbits using end points frequently evaluated in toxicity studies: testicular weight and testicular histology. Testicular weights and testicular maturity as assessed histologically were markedly variable in sexually immature rabbits, especially at > or = 14 weeks of age. The large variation in testicular weights in immature rabbits requires that large changes in a treatment group relative to controls be present for statistical detection of testicular weight effects at commonly used significance levels. Testicular weights and testicular maturity were strongly correlated to one another, but neither weight nor maturity was strongly correlated to body weight. Thus, stratification and randomization of immature rabbits to study groups based upon body weight will not assure an absence of group differences with respect to testicular maturity. The large variation in testicular weights and maturity in 13-17-week-old rabbits warrants caution in the evaluation of testicular changes when rabbits of this age range are used in toxicity studies.