Determination of true ileal digestibility of phosphorus of fish meal in broiler diets

The objective of this study was to determine the true ileal digestibility coefficient (TIDC) of phosphorus (P) from fish meal (FM) using direct, difference, and regression methods. Six experimental, semi-purified diets were formulated: free diet - based on corn starch and sugar, free of calcium and phosphorus; FM4- inclusion of 40 g/kg fish meal; FM7 - inclusion of 70 g/kg fish meal; FM10 - inclusion of 100 g/kg fish meal; DP - addition of phosphorus from dicalcium phosphate (DP); and DP + FM - half of the phosphorus supplied by dicalcium phosphate, and the other half by fish meal. The Ca- and P-free diet was used to determine endogenous losses of phosphorus, necessary for the correction of apparent values to obtain true values in the direct and difference methods. The diets FM4, FM7, and FM10 were used to determine the coefficient of digestibility by the regression method. FM10 was also used to determine digestibility by the direct method, and the DP and DP + FM diets were used to determine the TIDC by the difference method. Titanium dioxide was added at a concentration of 3 g/kg to all the diets as an indigestible marker. A total of 252 broilers were housed in metabolic cages, and the diets were distributed in a completely randomized design, consisting of six treatments, with six replicates of seven broilers each. The broilers were fed the experimental diets for three days, from 19 to 22 days of age. At 22 days of age, broilers were euthanized, and the ileal digesta was collected. The digesta and diets were analyzed for titanium, dry matter, and phosphorus. The apparent digestibility of phosphorus in the experimental diets was calculated using the indicator method. The ileal endogenous loss, using the Ca- and P-free diet, was calculated as 128.7 mg/kg of dry matter intake (DMI); however, ileal endogenous loss estimated using the regression method was negative (-1062 mg/kg DMI). The TIDC of phosphorus determined by the direct, difference, and regression methods was 0.455, 0.517, and 0.255, respectively. The lowest digestibility of phosphorus was found with the regression method, which might be related to the negative value obtained for endogenous loss. This study showed that the direct method was the most accurate for the determination of true phosphorus digestibility.