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

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

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

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?