Response of broiler chickens offered choices of feeds varying in calcium and phosphorus concentration from 0 to 21 days of age

1. This study tested the ability of broiler chickens to regulate dietary calcium (Ca) and retainable phosphorus (rP) intake when offered choices of complete diets varying in Ca and rP concentration from 0 to 21 d of age.2. Males and females were reared separately under standard conditions and offered either a single diet in some treatments, or in other treatments, a choice of two diets varying in Ca and rP concentration, resulting in 10 dietary treatments. Body weight and feed intake were measured at 7, 14 and 21 d. For each choice treatment, the intake of each diet as a proportion of the total intake was determined. Tibial ash concentration, Ca concentration, phosphorus (P) concentration and breaking strength were determined at 21 d.3. For the choice treatments, in which one diet was low in rP and the other high in rP, feed intake significantly favoured high rP concentration. Body weight gain responded positively to increasing rP intake, apparently regardless of Ca intake, although bone density and structural integrity were maximised when rP and Ca intake were both high.4. The principle that broiler chickens can select between feedstuffs to achieve intake that maximises growth, and, arguably, fitness, was seen in the diet choice of broiler chickens in the current experiment, at least for dietary Ca and rP.