The Seasonal Reproductive Condition of Male Brown Rats in Baltimore, Maryland

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Abstract
Descr. of the condition of the reproductive organs of 721 male rats collected from comparable habitat conditions during a period of 14 mos. The rats were trapped in poultry warehouses which have abundant food and harborage and weather conditions almost the same as out-of-doors. At autopsy data were obtained concerning the physical characteristics and the reproductive condition of the males. For analysis the year was divided into 7 biological seasons, dependent upon precipitation and temp. There is no evidence of seasonal changes in the size of tie testes, the seminal vesicles, ventral prostate, or Cowper''s gland,nor in the presence of sperm. A satisfactory field criterion for activity of the testes is visibility of the seminiferous tubules through the tunica albuginea. Several characters may be used to indicate relative ages of rats. The wts. at which 50% of the rats have the following characters are: eruption of 3rd molar (67[plus or minus]17 g.); ossification of the skull (92[plus or minus]20 g.); descent of the testes (105[plus or minus]45 g.); presence of sperm (200[plus or minus]70 g.). It is concluded that in contrast to most rodents, male rats living in Baltimore are fertile throughout the year. Seasonal changes in reproductive rates apparently depend upon the female.

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