In fact Gall bladder is absent Albino rats and Ruminants.

Here the function of gall bladder like Concentraction of bile is performed by cells linning the ducts of Hepato biliary system.

There are several species, where a gall bladder is physiologically absent, like the horse, giraffe, tapirs and several kind of birds. The hepatic bile ducts concentrate to a certain extent the bile produced by hepatocytes.

Dear Mohammad,

You can find some possible answers below:

https://biology.stackexchange.com/questions/43983/why-dont-rats-have-a-gallbladder-unlike-other-rodents