How old are they? A hybrid meat bird will be of slaughtering age in 8 to 12 weeks depending on feed and if cockerels or pullets and your dress weight will range in that age from 3 to 5 lbs. Dual purpose take longer, I've slaughtered dual cockerels at 14 weeks and gotten 3 lb dress weight so you can tell by their growth if they are White Rock dual purpose or Cornish Cross meat bird.