Sideloading with Ember ActiveModelAdapter and Rails

I have two models:

user: [ 
  firstName: DS.attr('string'),
  lastName: DS.attr('string'),
  animals: DS.hasMany('animal', { async: true })
]

animal: [ 
  name: DS.attr('string'),
  user: DS.belongsTo('user', { async: true })
]

When I see animals route all works fine, the JSON that rails return is like:

{"animals":[{"id":1,"name":"Wiskey","user_id":3}

and Ember call a GET for the user/3.

When I try to find all users what I have is this json:

{"users":[{"id":3,"firstName":"Bob","lastName":"Marley","animal_ids":[4,8,14]}

but no GET was call for the animals 4, 8 and 14. What is the problem? The adapter that I use is ActiveModelAdapter.

Thanks!