Cobb and Aviagen have numerous strains for different parts of the industry.
You have Cobb 700, Cobb 500, Cobb 500 Slow,, Ross 308, Ross 308AP, Ross 508, Ross 708, Hybro Plus and Avian 48, Rowan 708, Rowan Ranger , Ranger Premium, Ranger Classic, etc
There is also nothing like GMO in the production chicken strains.. There is no lab gene manipulation its strait breeding thru carful analysis of the genetics.
You also can get 100% survival with standard CX.. I just finished 60 birds no losses ad lib feed thru 4 wks and could have gone longer.. Things like 17hr/day of light not more, good quality soy free feed.. electrolyte probiotic mix pastured treated to meal worms. All help to raise healthy birds.. Birds were taken at 7.5 wks as that was when it in the schedule. Pullets average including necks 6.3 Cockerels average over 8 with necks.. No bird was under 5. They were not small birds.
There are a number of research studies showing the negative health effects of soy in feed on broiler and chickens in genera
l.