Havenstein et al. (2003a), for instance, compared performance traits of Athens Canadian Randombred Control (ACBRC), a strain established in 1957 which is still maintained, and
Ross 308, when fed either a diet representative for1957 or a modern diet, representative for 2001.
These authors demonstrated an almost fourfold increase in bodyweight at age 42 days on account of significant improvements in both genetics and nutrition, of which over 90% could be attributed to selection efforts. Further, FCR significantly improved with 30%, of which 80% on account of improved genetics. However, mortality increased numerically with
100%, feed and genetics being equally involved. An
important unfavourable consequence of persistent
selection towards fast growing, high yielding broiler
strains is a significant decrease in relative cardiopulmonary
capacity