Annual Changes in Serum Testosterone in Laboratory Housed Male Stumptail Macaques (M. arctoides)

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Abstract
Serum testosterone levels were estimated at monthly intervals over more than 2 yr in 6 male stump-tailed macaques housed in the laboratory under strictly controlled light and temperature conditions. Serum testosterone varied significantly throughout the year with peak levels in June (14.77 ng/ml) and low levels in Sept. (6.67 ng/ml). Serum testosterone levels did not correlate with ejaculatory behavior of the males. Birth records of 62 live young, born over an 8 yr period in the stump-tailed macaque breeding program of the Dutch Primate Center [The Netherlands] were also examined. The records revealed a rather uniform frequency of monthly births occurring throughout the year. The low frequencies in the Nov.-Feb. period are probably due to the method of breeding employed. No breeding occurred during the summer months.