title: Possible influence of strain differences on pregnancy initiation in laboratory rats.
abstract: Recent research in this laboratory has failed to replicate previous findings that the first ejaculatory series of the male is sufficient to induce a high incidence of pregnancy in female laboratory rats (Rattus norvegicus). The incidence of pregnancy and pseudopregnancy in albino and hooded females were compared in a standard experimental paradigm. Eight percent of Sprague-Dawley albino females exhibited a progestational response, while 45% of the Long-Evans hooded females became progestational. On the basis of these findings, and a lack of previous formal comparison of genetic strains, it is suggested that genetic differences among strains may be at least partially responsible for differences observed in the ability of a single ejaculatory series to impregnate female laboratory rats.
mesh_terms: D000818:Animals; D005260:Female; D005298:Fertility / Q000187:drug effects*; D006801:Humans; D008297:Male; D011247:Pregnancy; D011555:Pseudopregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D012726:Sexual Behavior, Animal / Q000187:drug effects*; D013045:Species Specificity