large breasted males have trouble keeping balance to breed. The largest of my cx mix roos had trouble by 14 months.  I seen the hens were looking ratty and started watching chicken porn. For ever 6 times they made connection once. The heritage made it most of the time.  The largest started dying at 16 months, one lasted 2 1/2 yrs. Thee were out of a cx hen and were white. I have some descendants that are barred roos I am using this year, the breast is not as large but bigger than heritage.
 artificially inseminated would be an option.... if that's your thing 
