The Duration of the Trial Influences the Effects of Mineral Deficiency and the Effective Phytase Dose in Broilers’ Diets

SIMPLE SUMMARY: The aim of this work was to investigate the effects of reducing the mineral (Ca and P) content and the addition of different doses of a new 3-bacterial phytase in broiler diets in a short- and long-term experiment. Mineral deficiency reduced growth performance only in young animals, and it increased Ca and P digestibility and reduced tibia mineralization, especially in the long-term trial. The effective dose of the new phytase varied with the response criteria and duration of the trial. Phytase increased feed efficiency at 500 FTU/kg, but only in young animals, and increased mineral digestibility and retention at a lower dose (250 FTU/kg) in the short- compared with the long-term (500 FTU/kg) trial. Tibia mineralization increased with only 250 FTU/kg in the long-term trial. Therefore, the age of the animals and duration of the trial are key in determining the effects of mineral levels and phytase addition in broiler feed and should be taken into account for future trials. ABSTRACT: Two trials varying in duration (short- and long-term) were conducted to evaluate the effects of providing deficient (NC) or sufficient (PC) Ca and P levels, and different doses of a new phytase (250, 500, and 1000 FTU/kg feed), in broiler feed on growth performance, nutrient digestibility and retention, and tibia mineralization. A total of 80 and 490 male chicks (Ross) of 21 and 1 days of age were used in the short- and long-term trials, respectively. In the long-term trial, chicks fed NC diets showed a lower (p < 0.05) average daily gain and feed intake compared to chicks fed PC and a greater (p < 0.05) feed conversion ratio compared to 500 and 1000 FTU/kg feed during the starting period. Regarding the effects on minerals’ and nutrients’ coefficients of retention, animals fed NC showed a significantly higher digestibility for P than those fed the PC diet in the long-term trial. Additionally, feeding 250 to 500 FTU/kg diets increased most of the nutrients’ digestibility in the short-term but only P digestibility in the long-term trial. Tibia mineralization increased linearly with phytase addition (p < 0.05) only in the long-term trial. In conclusion, the effects of dietary mineral and phytase levels on growth performance are more noticeable in young animals. In addition, the duration of the trial is key due to a possible adaptation phenomenon of birds to low P supplementary levels.