Effect of phytase inclusion and calcium/phosphorus ratio on the performance and nutrient retention of grower–finisher pigs fed barley/wheat/soya bean meal-based diets

Two experiments were conducted to evaluate the effects of phosphorus (P) level and calcium (Ca)/total P (tP) ratio on the efficacy of microbial phytase. Experiment 1 examined the effects of P concentration and microbial phytase inclusion on mineral excretion and pig performance, while experiment 2 examined the effects of Ca/tP ratio and microbial phytase inclusion on mineral excretion and pig performance. In experiment 1, nutrient and mineral digestibility (n = 4) and growth performance (n = 12) were determined in pigs individually fed diets containing (T1) 5.5 g kg−1 tP, 2.3 g kg−1 available P (aP) and 8.0 g kg−1 Ca, (T2) 5.5 g kg−1 tP, 2.3 g kg−1 aP, 8.0 g kg−1 Ca and 750 FYT kg−1Peniophora lycii phytase, (T3) 4.3 g kg−1 tP, 1.4 g kg−1 aP and 8.0 g kg−1 Ca and (T4) 4.3 g kg−1 tP, 1.4 g kg−1 aP, 8.0 g kg−1 Ca and 750 FYT kg−1P lycii phytase. In experiment 2, nutrient and mineral digestibility (n = 4) and growth performance (n = 12) were determined in pigs individually fed diets containing (TT1) 4.3 g kg−1 tP and 8.0 g kg−1 Ca, (TT2) 4.3 g kg−1 tP, 8.0 g kg−1 Ca and 750 FYT kg−1P lycii phytase, (TT3) 4.3 g kg−1 tP and 5.0 g kg−1 Ca and (TT4) 4.3 g kg−1 tP, 5.0 g kg−1 Ca and 750 FYT kg−1P lycii phytase. All diets were formulated, using standard feeding values for the ingredients, to have similar concentrations of digestible energy (DE) and lysine. In experiment 1, pigs offered the low-P diets had significantly lower P intake (P < 0.001), faecal P excretion (P < 0.05), Ca intake (P < 0.05) and faecal Ca excretion (P < 0.05) compared with pigs given the adequate-P diets. These pigs also had significantly lower daily gain (P < 0.01), feed intake (P < 0.05) and feed conversion ratio (FCR) (P < 0.05). The inclusion of phytase in both the adequate- and low-P diets increased the digestibility of energy (P < 0.05) and Ca (P < 0.01) but had no effect on pig performance. In experiment 2, lowering the Ca/tP ratio from 1.85:1 to 1.15:1 increased the DE content of the diet (P < 0.05). The inclusion of phytase increased (P < 0.05) the digestibility of protein (0.874 versus 0.840, SEM 0.009) and Ca (0.427 versus 0.380, SEM 0.019) as well as the DE content of the diet (14.47 versus 14.26 MJ kg−1, SEM 0.073). There was a significant ratio × phytase interaction (P < 0.5) for P digestibility. Microbial phytase significantly increased P digestibility when added to the 1.15:1 ratio diet but had no effect when added to the 1.85:1 ratio diet. The inclusion of microbial phytase increased feed intake (2.16 versus 2.00 kg day−1, SEM 0.05; P < 0.05) and weight gain (0.893 versus 0.818 kg day−1, SEM 0.022; P < 0.05). Lowering the Ca/tP ratio resulted in a significant improvement in FCR (2.32 versus 2.40 kg kg−1, SEM 0.03; P < 0.05). In conclusion, the beneficial effects of microbial phytase supplementation of pig diets are adversely affected by a wide Ca/tP ratio.