It looks to me like you have set up your farm for .htaccess but are trying to access your animals using the virtual host type urls. In the .htaccess method you will have your farmer and the animals in two separate directories on the same level:
And your url to access animal_1 should be http:/mydomain/barn/animal_1
In the virutal host style, you have to set up your virtual hosts in your apache configuration and there is no farmer as such. Instead there is a directory which holds a complete dokuwiki, which is in effect the farmer, and inside that dokuwiki directory you have your animals. So if your farm domain is vfarm.com:
So check your farm setup to see which has been installed on your server.
I'm not familiar with the farmer plugin and so don't know how it sets up the farm.