Availability for growing pigs of minerals and protein of a high phytate barley-rapeseed meal diet treated with Aspergillus niger phytase or soaked with whey

The improvement of phytin-phosphorus utilization in barley-rapeseed meal (800 and 200 g kg−1) diet due to Aspergillus niger phytase (EC 3.1.3.8) supplement was assayed in a 8 × 6 cyclic change over designed digestibility and balance trial with eight growing pigs of 28–70 kg live weight. The 2 × 2 × 2 factorially arranged diets were either fortified with dicalcium phosphate to supply total phosphorus (P) 6.7 and available P (aP) 2.8 g kg−1 or without inorganic P supplement, P 5.3, aP 1.4 g kg−1; were fed either as soaked with whey at 40 °C for 3 h or without soaking; and half the diets were supplemented with phytase 1000 PU g−1 (Finase® FP500). Each diet contained calcium (Ca) 8.0 g kg−1. Other nutrients were at similar levels in each diet. Soaking of the meal with whey significantly improved ash and organic matter digestibilities (P < 0.001). The digestibilities of ash (P < 0.001) and ether extract (P < 0.05) were enhanced (2 and 3% units) by phytase treatment. No effect on nitrogen (N) utilization was found due to phytase addition, but soaking significantly improved N retention in relation to N intake. Both the soaking of the diet and addition of microbial phytase significantly improved (P < 0.01, P < 0.001) the apparent absorption of P (3 and 9% units). The retained P in diets with supplementary phytase was significantly higher (P < 0.01) than that without, 3.8 vs. 2.8 g day−1. The soaking had an enhancing effect on P retention. P retention in relation to intake was greater (P < 0.001) in diets with added phytase than without (36 vs. 31%). From the diet with inorganic P supplementation a significantly lower retention value, 29% (P < 0.001), was achieved compared with the P-unsupplemented diets. Phytase supplementation did not affect Ca absorption but significantly increased Ca retention due to lower urinary excretion. The soaking had no effect on Ca absorption or retention. Utilization of magnesium and zinc was not affected by the treatments. The results indicate that microbial phytase and soaking with whey improved the utilization of phytate P in barley-rapeseed meal diet and reduced the amount of P excretion in faces.