Pubertal endocrinology of yellow baboon (Papio cynocephalus): Plasma testosterone, testis size, body weight, and crown-rump length in males.

A cross-sectional study (n = 99) was made of male baboons (Papio cynocephalus) aged 3 weeks to > 10 years. Serum testosterone and testicular size were compared with body weight and crown-rump length. Pubertal onset in baboons occurs at 3-4 years of age; data were analyzed, therefore in three groups: 0-3 years; 3-4 years; and greater than 4 years. Testicular volume index increased minimally prior to 3 years of age. Between 3 and 4 years of age, there was an increase (P < .05) in testicular growth, which was followed after 4 years of age by a return to the prepubertal rate. Plasma testosterone decreased from birth to 3 years of age. Between 3 and 4 years of age, there was an increase (P < .05) in testosterone. The levels of which remained unchanged after 4 years of age. A linear increase in body weight was observed for the first 3 years which was followed by an increase (P < .05) in the rate of weight gain between 3 and 4 years of age. After 4 years of age, body weight continued to increase but at a rate less than those of the two earlier periods. A linear increase in crown-rump length was observed over the first 3 years. Between 3 and 4 years of age there was a slight increase (P > .06) in crown-rump length, which approached zero after 4 years of age. These data demonstrate many similarities between the pubertal development of male baboons and humans. Male baboons appear to be appropriate for the study of reproductive and endocrine development and the factors involved in the pubertal growth spurt of the human male.