Sexual maturation and fecundity of wild and domestic Norway rats (Rattus norvegicus)

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Abstract
A population of captive-reared wild Norway rats and 2 stocks of domestic rats were compared for various parameters of sexual maturation and fecundity. Males did not differ in age at the 1st appearance of spermatozoa in the testes but wild males, were significantly older than Long-Evans and Spraque-Dawley domestic males at 1st copulation with a hormone-induced estrous female. Wild females were significantly older than domestic females at the time of vaginal opening, 1st estrus and 1st conception. Stocks did not differ in length of the 1st estrous cycle. Wild females produced significantly smaller litters than their domestic counterparts. Domestic rats were significantly heavier than wild rats at the various stages of sexual maturation. Domestication of the rat apparently has been accompanied by genetic and/or environmental changes that accelerate sexual development and improve breeding success under laboratory conditions.

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