PSVI-4 Effect of phytase on mineral digestibility and growth performance of pigs fed diets with pharmacological levels of Zn

An experiment was conducted to test the hypothesis that increasing levels of phytase increases mineral digestibility and growth performance of pigs fed diets with 3,000 mg/kg of Zn. A positive control (PC) diet that met nutrient requirements and a negative control (NC) diet that was deficient in total Ca (-0.16%), digestible P (-0.14%), metabolizable energy (-50 kcal/kg), and digestible amino acids (-0.02%) were formulated. Eight additional diets were formulated by adding 500, 1,000, 1,500, or 2,000 phytase units/kg of a novel bacterial 6-phytase (PhyG) or a commercial Buttiauxella phytase (PhyB) to the NC diet. A randomized complete block design with 400 weanling pigs (5.82 ± 0.70 kg), 10 diets, 4 pigs per pen, and 10 replicate pens per diet was used. Pigs were fed the experimental diets for 28 d. Fecal samples were collected from 1 pig per pen on d 26 to 28. Linear and quadratic effects of PhyG and PhyB were determined using polynomial contrast statements. Contrast statements were used to compare effects of PC diet with NC diet, and to compare effects of PhyG diets with PhyB diets. Overall, pigs fed the NC diet had reduced growth performance (P < 0.05) compared with pigs fed the NC diet (Table 1). Linear (P < 0.01) and quadratic (P < 0.05) increases in overall average daily gain and average daily feed intake of pigs were observed as dietary concentrations of PhyG or PhyB increased. Increasing levels of PhyG or PhyB linearly increased (P < 0.01) the apparent total tract digestibility (ATTD) of P and Ca. PhyG increased ATTD of P more (P < 0.05) than PhyB. In conclusion, both phytases are effective in increasing mineral digestibility and growth performance in pigs fed diets with pharmacological levels of Zn; however, PhyG improved P digestibility more than PhyB.