The effects of microbial phytase, organic acids and their interaction in diets for growing pigs

One hundred and ninety-two crossbred pigs from 22 to 45 kg BW were used to investigate the effects of Aspergillus niger phytase, organic acids, and their interaction, on animal performance, nutrient digestibility and urine composition. Pigs were housed in pens of six animals each, and had ad libitum access to the pelleted feed and water. A basal diet was either or nor supplemented with 410 phytase units kg(-1), and with lactic acid (0; 16.0 and 32.0 g kg(-1)) or formic acid (0, 8.0 and 16.0 g kg(-1)). The respective levels of lactic acid and formic acid were of the same acid equivalency. There were four replicates for the basal diet either or not supplemented with microbial phytase, and three replicates for the other treatments. The Ca and digestible P contents of the basal diet were 6.0 and 1.0 g kg(-1), respectively. The apparent total tract digestibilities of DM, OM, ash, Ca, Mg and P were calculated using Cr2O3 as an indigestible marker. Osmolarity, pH, Ca, Mg, and P content were analysed in freshly voided urine. Microbial phytase very positively affected animal performance. Also, their daily gain and feed conversion ratio were significantly enhanced by the organic acids, but there was no synergistic effect. The apparent total tract digestibility of DM, ash, Ca and P were significantly enhanced by microbial phytase. Also, the apparent total tract digestibility of DM, OM, ash, Ca and P were significantly enhanced by the organic acids. A synergistic effect of organic acids and microbial phytase was found for ash, P and Mg digestibility. Formic acid and phytase increased digestible P content by 0.20 g digestible P kg(-1) of diet. No differences in the effect due to the doses of supplemented organic acids were observed on animal performance, digestibilities and urine characteristics. Microbial phytase affected Ca and P content in urine, but had no effect on pn, osmolarity and Mg content. The acids had no effect on urine parameters. (C) 2000 Elsevier Science B.V. All rights reserved.