Are fast growing broilers more efficient when fed the same daily feed quantity as a slower growing strain?

Current fast growing broilers are selected for high feed intake and breast meat yield. In order to separate the effects of feed intake, growth rate and age, a quickly growing strain (Ross 308) was restricted fed (R-R) the same daily quantities of conventional diets as ad lib fed broilers (S-AL) of a slower growing strain (Sasso T451). As positive control group, Ross broilers were also fed ad lib (R-AL). Each treatment consisted of four pens (two males and two females) with 25 chicks each. Daily weight gain and feed intake were recorded weekly. At 40 and 62 days of age, 4 broilers were slaughtered out of each pen, and yield, carcass cuts and composition were determined. Feed efficiency between 0 and 40 days was significantly better in R-R than in S-AL broilers (0.561 vs 0.525, respectively). This difference increased with age: 0.529 vs 0.433 between 0 and 62 days, resulting in a final weight of 3,029g and 2,516g, respectively (P<0.01). Chicken slaughter yield at 62 days of age was 66.6% and 65.1% for R-R and S-AL chickens respectively, which was significantly lower than R-AL chickens at 40 days (70.5%). Feed restriction till the intake of a slower growing strain reduced breast meat (30.3%) compared to R-AL (33.4%) but was still much higher than in S-AL broilers (23.9%). Carcasses of restricted broilers were leaner (8.9%, 14.8% and 12.0% fat in R-R, S-AL and R-AL, respectively) and contained a much higher (P<0.01) water content: 70.7%, 63.4% and 68.4%, respectively.