Effect of dietary nonphytate phosphorus and calcium concentration on calcium appetite of broiler chicks

The effect of dietary nonphytate P (nPP) and Ca concentration on the Ca appetite in broilers was evaluated. A total of 288 one-day-old male Ross 308 broilers were fed a commercial diet for 7 d then randomly allocated to 1 of 8 dietary treatments for a 28-d study. Diets were corn-soybean meal based and formulated to be nutritionally adequate except for nPP and Ca. Two concentrations of Ca (5.0 and 10.0 g/kg) and 4 of nPP (2.5, 3.5, 4.5, and 5.5 g/kg) were used, and all birds had access to a separate Ca source (CaCO₃). Bird performance, nutrient digestibility, and tibia ash were determined. Birds fed 5.0 g of Ca/kg diets consumed more (P < 0.01) of the separate Ca source than birds fed diets containing 10.0 g of Ca/kg. Increased consumption (P < 0.01) of the separate Ca source was associated with increasing nPP concentration. Bird performance was not influenced by dietary treatment. Birds fed 5.5 g of nPP/kg diets had lower (P < 0.01) digestibility of DM, CP, and energy than the other groups. Phosphorus digestibility was reduced in birds fed high Ca diets and those fed 2.5 g of nPP/kg diets (P < 0.001). Birds fed 2.5 g of nPP/kg had lower tibia ash values than those fed higher concentrations of nPP while feeding diets containing 10.0 g of Ca/kg led to higher concentrations (P < 0.05) of tibia ash than for birds fed 5.0 g of Ca/kg. This study confirms previous findings that birds are able to meet their Ca requirement when fed Ca separately from the mixed ration. Consumption of the separate Ca source responded to not only Ca concentration but also to the amount of nPP in the diet. These data suggest that dietary nPP concentration influences the Ca specific appetite of broilers, and this may indicate that birds attempt to regulate their intake of Ca relative to nPP. This may be mediated via a physiological mechanism to maintain an appropriate Ca:nPP intake.