Research Note: Formulating broiler diets using digestible calcium significantly improved growth performance but reduced apparent ileal digestibility of calcium and phosphorus.

An experiment was conducted to compare the use of a total and digestible Ca formulation system in broilers from hatch to d 37 post-hatch. Ross 308 (n = 288) male broilers were obtained and allocated to one of 2 dietary treatments in floor pens. There were 18 birds per pen and 8 replicate pens per diet. One diet was formulated using ingredient and nutrient recommendations for total Ca and the second diet was formulated using ingredient and nutrient recommendations for standardized ileal digestible (SID) Ca. All diets were formulated to be nutrient adequate using a 2-phase feeding program and including 0.19% available P (avP) and 0.209% total Ca or 0.073% digestible Ca from 1,000 FYT/kg of phytase. On d 17 and 37, tibias and ileal contents were obtained. From hatch to d 37, birds fed diets formulated using digestible Ca gained (P < 0.05) more and were more efficient (P < 0.05) compared with birds fed diets formulated using total Ca. There was no impact of formulation system on tibia ash or minerals. Litter pH (P < 0.05) was greater and litter dry matter (P < 0.05) was lower in birds fed the diets formulated using digestible Ca compared with those fed diets formulated using total Ca. Apparent ileal digestibility (AID) of Ca (P < 0.05), AID of P (P < 0.05) and digestible P intake (P < 0.05) were lower in birds fed diets formulated using digestible Ca compared with those formulated using total Ca at d 17 or 37. However, apparent ileal digested Ca and digestible Ca intake were not different between the experimental diets on d 17 or 37. In conclusion, formulating diets using digestible Ca improved weight gain and feed conversion ratio, but reduced the AID of Ca and P compared with birds fed diets formulated using total Ca. These findings might be reflective of the higher total Ca concentration in the diets formulated using digestible Ca compared with those formulated using total Ca.