Efficacy of Optiphos phytase on mineral digestibility in diets for breeding sows: effect during pregnancy and lactation

Phosphorus in most diets for breeding sows is digested for 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 Optiphos TM phytase derived from E. coli and produced by the yeast Pichia pastoris. Thirty crossbred gestating sows and 36 lactating sows were used in these studies. Five treatments were imposed on the gestating sows: 1) a negative control treatment, based on a low-P diet without added feed phosphate and microbial phytase. Diets in Treatments 2, 3 and 4 were the same as the negative control diet, except that an amount of Optiphos phytase of 125, 250 and 1,000 U.kg -1 of diet, respectively, was added. Treatment 5 was the positive control diet, based on the same diet with 1.0 g of added digestible P.kg -1 of diet from monocalcium phosphate. The lactating sows of Treatments 1 to 6 received a negative control diet, the same diet with an amount of Optiphos TM phytase of 125, 250, 500 and 1000 U.kg -1 of diet and a positive control diet supplemented with 1.5 g of digestible P.kg -1 , respectively. The negative control diets were different in ingredient composition because of the different nutrient requirements between lactating and gestating sows. The ratio between Ca and digestible P was kept at 2.8:1 and 3.3:1 for the lactating and gestating diets, respectively, with a minimum of 5.0 g Ca.kg -1 . 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 the piglets at 4 weeks of age and the gestating sows from day 49 to day 100 of pregnancy. Faecal samples of the sows were collected by rectal stimulation on days 14 and 21 post-farrowing, and on days 70 and 100 of pregnancy. Digestibility coefficients of dry matter, organic matter, ash and the minerals under investigation were calculated using Cr2O3 as an indigestible marker. In addition, several performance characteristics were registered. Phosphorus digestibility was clearly enhanced by the addition of microbial phytase to the lactating sow diets, as was the digestibility of ash, Ca, Na, K, Cu, and Zn. In the gestating sows only digestibility of P was significantly enhanced by microbial phytase. In both gestating and lactating sows the lowest level of phytase addition (125 U.kg -1 of diet) already resulted in the highest response in P digestibility without further improvement at higher phytase inclusion levels. The additional amount of digestible P absorbed with a phytase supplement of 125 or more U.kg -1 in lactating sows was on average 0.90 g/kg. An average amount of 0.36 and 0.67 g digestible P.kg -1 was generated in gestating sows at day 70 and day 100 of pregnancy by this phytase inclusion, respectively. No signs of any adverse effect of phytase on sow or piglet health and performance were observed. Optiphos TM phytase was already highly effective at a dose of 125 U.kg -1 of diet. Possible reasons for the lack of further improvement of P digestibility at higher doses of phytase are discussed. If feed phosphates are (partly) replaced by 125 U phytase.kg -1 of diet, then P excretion can be reduced by 0.85 kg.sow -1 .year -1 .