Effect of varying protein levels on carcass composition and nutrient utilization in 2 lines of chickens divergently selected for oxygen consumption
Stewart, P.A.; Muir, W.M.
Poultry Science 61(1): 1-11
A replicated experiment was initiated to investigate the response of 2 populations of chickens, divergently selected for high and low O2 consumption, to varying protein levels. A 3 .times. 4 factorial arrangement of 4 isocaloric protein diets (16, 18, 22 and 26%) and 3 levels of intake (100, 80 and 60% of ad lib) were randomly assigned to 24 pens, resulting in 2 pens/treatment combination for each line. Chicks  from each line were then randomly assigned to the 24 pens, 10 chicks/pen. Criteria measured on a per pen basis were weekly body weight gains, daily feed intake, metabolizabe energy (ME) values of the diets and changes in carcass moisture, N, fat and energy. Statistical analysis indicated that feed efficiency and weight gains of the low O2 birds were greater at all protein levels studied than the high O2. Carcass composition data indicated that the low O2 birds gained more lean and less fat tissue than the high O2 birds both totally and as a percentage of dry matter gain. Low O2 birds also were more efficient in the utilization of N, but there was no difference between the lines in the efficiency of ME utilization. The low O2 birds were slightly superior in net energy utilization, as would be expected since they were depositing more lean tissue. Selection for low O2 consumption, therefore, has resulted in a faster growing, leaner and more efficient bird.