ActiveRecord 3 group+select

Hi guys, I'm trying to figure out how to chain together group and select, two finder methods in ActiveRecord 3.x so I have this model

class Cow < ActiveRecord::Base    set_table_name :cows    belongs_to :farmer end

with breed:string and milk_quantity:integer columns and in client code:

result ="breed,sum(milk_quantity) as s").group('breed').all

that runs this query

SELECT breed,sum(milk_quantity) as s FROM "cows" GROUP BY breed

And the rdb results are right :

first breed --->100 second breed --->200

and so on..

My question is: How can access sum(milk_quantity) result from result array of Cow?