Hi everyone!

What differ a strain of animals from breeds of animals? In my opinion animals of different breeds differ in more external appearance, rather than physiologically. For example, dogs French bulldog and German shepherd. The laboratory rats or mice for external appearance not differ as dogs. But physiological very differ. For example, Wistar rat's strains more often develop spontaneous cancer than Sprague-Dawley. The Wistar-Kyoto rats have high blood pressure etc. In my opinion should be specified as inbred or outbred animals, noting the name of the breed (Wistar, Sprague-Dawley, CD-I, Swiss Webster etc).

The basic difference is how they are derived. Breeds are, well, bred. Strains usually have smaller defined genomic differences. Note that there is an overlap, as defined strains could be derived from breeding. However, all individuals within a strain are genetically uniform.

Thank you for your reply. But I think the term "breed" for the varieties types of dogs and laboratory rats are not the same.