Why the monoclonal Ab麓s are made in mouse and the polyclonal Ab麓s are made in rabbit

The answer to this is more related to the availability of materials and less related to specific characteristics of these species.

The availability of non-producing plasma cell tumor and autonomously dividing cell line in the mouse makes it possible to fuse a normal antibody producing B-cell with the plasma cell tumor cell and have it grow and produce antibodies continuously. The men who developed this procedure Koehler and Milstein were awarded the Nobel prize for it because this procedure has become extremely valuable in all biological sciences and in medicine. These antibodies are called monoclonal antibodies because they are made by the daughters of a single antibody producing cell. Monoclonal antibodies bind to only one specific antigenic component called an epitope. This makes monoclonals very specific which is useful in science and medicine but these antibodies usually don't bind very tightly.

On the other hand, Rabbits develop antibody diversity shortly after they are born. This makes it possible for laboratories to make large amounts of antibody to a specific antigen by injecting very young Rabbits with the antigen which becomes the main focus of the antibody diversification process. These young rabbits make lots of different antibodies to the antigen or to specific amino acid sequences or conformations of it. The effect of having multiple kinds of antibody made by multiple clones of antibody producing cells (which is why these are called polyclonal antibodies) is to have an antibody that binds to the antigen very tightly. Such antibodies are available in large amounts and are used to purify specific proteins, capture other antibodies in assays, and passively protect against pathogens in infectious disease models, etc.