Phosphorus digestibility is highly influenced by phytase but slightly by calcium in growing pigs

Phytases are added to pig diets to render phytate phosphorus (P) available and improve P utilization. However, the efficacy of phytase may be influenced by dietary calcium (Ca). This experiment studied the interaction between phytase addition and dietary Ca. A wheat, barley and soybean meal diet without inorganic phosphate was used. Plant phytase was 650 FTU/kg DM in the not heat-treated diet. A 3*2 factorial design was used to evaluate the response of growing pigs to 3 levels of dietary Ca, 4, 6, 8 g Ca/kg as fed, and 2 levels of phytase, 0 and 750 FTU/kg. Ca was supplied as CaCO(3). Eight litters of 6 female pigs (40 kg) were kept in metabolism crates and fed one of the 6 diets for 12 d: 5 d for adaptation and 7 d for total collection of faeces and urine. No significant interaction between phytase and Ca was seen but phytase addition significantly increased P digestibility (from 38 to 58%) whereas the P digestibility was not significantly affected by Ca. In contrast, P retention and utilization was significantly affected by the interaction (p <= 0.001). When no phytase was added. P retention was 38% of P intake independent of Ca level. When phytase was added. P utilization increased from 42 to 55 and 57% when Ca was 4, 6 and 8 g/kg feed. This indicates that the pigs' Ca need was not met at 4 g/kg feed. Urinary and faecal P was affected by the phytase and Ca interaction. (C) 2010 Published by Elsevier B.V.