Efficacy of microbial phytase on mineral digestibility in diets for gestating and lactating sows

Phosphorus in most diets for breeding sows is digested from 20% to 40%, thus leading to a relatively high amount of P in the manure. To enhance the P digestibility in diets for both lactating and gestating sows, two separate experiments were carried out to study the efficacy of phytase derived from Peniophora lycii. Thirty crossbred lactating sows and 24 gestating sows were used in the studies. Five treatments were imposed on the lactating sows: (1) the negative control, a low-P diet without added feed phosphate and microbial phytase. Treatments 2, 3 and 4 were the same as the negative control diet, except that an amount of 750, 1000 and 10,000 U of phytase kg¿1 of diet, respectively, was added. Treatment 5 was the positive control diet, being treatment 1 with 1.5 g of digestible P added kg¿1 of diet from monocalcium phosphate. The gestating sows received the same first three treatments and a positive control diet supplemented with 1.0 g of digestible P kg¿1. The negative control diets were different in feedstuff composition. The ratio between Ca and digestible P was kept constant at 2.9:1 and 3.3:1 for the lactating and gestating diets, respectively. Feeding level of the sows was according to Dutch recommendations. Six sows per treatment were used. The lactating sows received the diets from 2 weeks before farrowing until weaning of piglets at 4 weeks of lactation and the gestating sows from day 49 to day 100 of pregnancy. Sampling of the faeces of the sows was done by rectal stimulation, and carried out at days 15 and 21 post-farrowing, and at days 70 and 99 of pregnancy. Digestibility coefficients of dry matter (DM), organic matter (OM), ash and the minerals under investigation were calculated using Cr2O3 as an indigestible marker. In addition, several performance characteristics were observed. Phosphorus digestibility was clearly enhanced by the addition of microbial phytase to the sow diets, as was the digestibility of ash, Ca, Mg, Na, K, Cu and Zn. There was a positive relationship between dose of phytase and the amount of liberated digestible phosphorus in lactating sows. The difference in liberated amount of digestible P between 1000 and 10,000 U kg¿1 was 0.34 g/kg of lactating diet. An amount of 0.77 and 0.42 g digestible P kg¿1 was liberated by 750 U/kg in the lactation and gestating diets, respectively. No signs of any adverse effect of phytase was observed on sow or piglet health and performance, even at a dose of 10,000 U kg¿1. The performance of piglets and sows at 10,000 U phytase kg¿1 was comparable to or better than the positive control diet. If feed phosphates are (partly) replaced by 750 U phytase kg¿1 of diet, then P excretion can be reduced by 0.75¿0.90 kg per breeding sow per year