Redirect to another controller+ action without changing URL in ASP.Net MVC3

Note: Below is just a small demo sort to simulate what i am looking for:

Below are the urls format on my app that user can see

mydomain.com/cat/1  --display cat with id 1 |controller=Cat, action=DisplayDetails
mydomain.com/dog/2  --display dog with id 2 |controller=Dog, action=DisplayDetails
mydomain.com/cow/2 --display cow with id 3  |controller=Cow, action=DisplayDetails

I have maintained a system where no 2 animals(may be of different kind) can have same id, it means if there is a cat with id=1, we cant have any other animal with that id. Also from my system i can extract animal details+ type just from animal id

Apart from existing URL pattern, I am planning to create a short Url in format as below

mydomain.com/1  --this will show cat
mydomain.com/2  --this will show dog
mydomain.com/3  --this will show cow

Routes i have created are as below, and they appear same order in global.asax

pattern= Cat/{id}, controller= Cat, action=DisplayDetails
pattern= Dog/{id}, controller=开发者_JAVA百科 Dog, action=DisplayDetails
pattern= Cow/{id}, controller= Cow, action=DisplayDetails
pattern= {id}, controller= DisplayAnyAnimal ----------i want help in this Route

Currently Controller looks like this

public class DisplayAnyAnimalContoller : Controller
{
      public ActionResult Index(string animalId)
      {
           //iam processing request here from animalId
           //now i know which contoller+action needs to be executed

          //say for instant i have to display dog with id=2

          //currently iam doing this to redirect and its working fine, 
          //but it changes url
          -----------------------------------------------
          #########################
          ### i need help here  ###       
          #########################
         return RedirectToRoute(new {contoller="Dog",action="DisplayDetails",id=2 });             
          -----------------------------------------------
      }
}

Now the problem with RedirectToRoute / RedirectToAction is they both changes the URL. But i dont want to change my url pattern.

Please suggest me how to achieve this, you may suggest some entirely different way, to achieve this

You could write a custom animal route:

public class AnimalRoute : Route
{
    public AnimalRoute(string url, IRouteHandler routeHandler)
        : base(url, routeHandler)
    { }

    public override RouteData GetRouteData(HttpContextBase httpContext)
    {
        var rd = base.GetRouteData(httpContext);
        var id = rd.GetRequiredString("id");

        // TODO: Given the id decide which controller to choose:
        // you could query the database or whatever it is needed.
        // Basically that will be the code you had in the beginning
        // of the index action of your DisplayAnyAnimalContoller which
        // is no longer needed.
        if (id == "1")
        {
            rd.Values["controller"] = "Cat";
        }
        else if (id == "2")
        {
            rd.Values["controller"] = "Dog";
        }
        else if (id == "3")
        {
            rd.Values["controller"] = "Cow";
        }
        else
        {
            // no idea what this animal was
            throw new HttpException(404, "Not found");
        }
        rd.Values["action"] = "index";
        return rd;
    }
}

and then register it in Global.asax:

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
    routes.Add(new AnimalRoute("{id}", new MvcRouteHandler()));
}

Now when you navigate to mydomain.com/1, the GetRouteData method of the custom route will be executed, will fetch the id=1, and then it will use the Index action of the Cat controller.