Efficacy of Trichoderma reesei phytase and acid phosphatase activity ratios in phytate phosphorus degradation in vitro and in pigs fed maize–soybean meal or barley–soybean meal diets

Efficacy of phytase together with different activity levels of acid phosphatase (AcPh) produced by transgenic strains of Trichoderma reesei in degrading phytates in maize, barley and soybean meal (SBM) was evaluated in vitro and in vivo with growing pigs. There was no interaction between the phytase (1000 PU g−1) and AcPh (7500 HFU g−1) dosage in the hydrolysing of phytates in any ingredients at pH 6.0. AcPh, however, complemented phytate dephosphorylation over that of phytase in barley and maize but not in SBM at pH 2.5, which is the pH optimum of the AcPh used. Barley–SBM and maize–SBM diets (800 : 200 g kg−1) without inorganic P (total P 4.1 g kg−1, available P 1.0 g kg−1) and supplemented with phytase 1100 PU kg−1 together with different activities of AcPh: 500, 4800, 7900 and 19 300 HFU g−1 were fed to growing pigs (36–69 kg live weight) in two 4 × 4 Latin square designed experiments. An increased AcPh level linearly improved (p < 0.05) the ash digestibility of maize-diets while no effect on other nutrients was found. The gradual increase of the AcPh level linearly improved (p < 0.05) the apparent absorption of P (3% to 7%-units) in both diets. The retained P in maize–SBM-diets with an increased level of AcPh was significantly improved (p < 0.05) from 3.5 to 4.0 g day−1 while the response in the barley–SBM-diet was smaller and non-significant. Ca retention increased linearly (p < 0.05) in maize–SBM-diets while no effect was noticed in barley diets due to the AcPh dosage. The results indicate that the synergistic interaction between microbial phytase and acid phosphatase activity levels is rather limited in degradation of phytates in barley, maize and SBM.