Growth, livability, and feed conversion of 1957 vs 1991 broilers when fed "typical" 1957 and 1991 broiler diets.

The relative contributions of genetic selection and dietary regimen on the performance of broilers was assessed. Body weight, feed consumption, mortality (M), and the degree of tibial dyschondroplasia (TD) were measured in the 1957 Athens-Canadian Randombred Control (ACRBC) strain of broilers and in the 1991 Arbor Acres (AA) feather-sexable strain when fed "typical" 1957 and 1991 diets. Energy and protein levels, vitamin and mineral packs, and the coccidiostats used in the two dietary regimens were chosen to be representative of those in use by the industry for the two time periods. Eight treatment groups, i.e., two strains, two sexes, and two dietary regimens, were assigned into four blocks of eight litter floor pens for grow out. The 1957 diets were fed as mash, and the 1991 starter and grower diets were fed as crumbles and pellets, respectively. Feed consumption and BW were recorded at 21, 42, 56, 70, and 84 d of age, a period covering the normal marketing ages for the two broilers. Mortality and the cause of death was recorded daily. The incidence and severity of TD was assessed using a Lixiscope at 42 d of age. Average BW were 190, 508, 790, 1,087, and 1,400 g for the ACRBC on the 1957 diets vs 700, 2,132, 3,108, 3,812, and 4,498 g for the AA on the 1991 diets at 21, 42, 56, 70, and 84 d of age, respectively. The 1991 diets increased the BW of the AA by an average of 14% (20% at 42 d, but only 8% at 84 d) and of the ACRBC by 22%. The BW advantage for the 1991 diet over the 1957 diet for the AA was less for males than for females after 42 d of age, and the advantage decreased with age, probably due to the increasing incidence of leg problems. The M for AA was 9.1% vs 3.3% for the ACRBC at 42 d. Most of the ACRBC M occurred before 21 d, whereas M occurred throughout for the AA, with most after 21 d due to flip-overs and ascites. The feed conversion at 42 d for the ACRBC on the 1957 diet was 3.00 vs 2.04 for the AA on the 1991 diet. The AA on the 1991 diet had a 48.6% incidence of TD vs 25.6% on the 1957 diet. The ACRBC had approximately 1.2% TD on both diets. The TD was more severe with the 1991 diet.