Simple SummaryPlants store phosphorus mainly in phytate form, which is slightly digestible by pigs due to the lack of native phytase. Some thermal processes, such as extrusion and exogenous phytase additives, can reduce phytate content in the diet, but the effectivity of the enzyme in diets including processed and unprocessed legume seeds needs to be better recognized. This study aims to investigate the effect of the addition of two phytase dosages to a diet containing raw lupine seeds and full-fat extruded soya seeds on the performance of growing pigs in terms of their carcasses, pork quality, and bone mineralization. Phytase significantly improved the pigs’ growth and feed utilization in the starter period and affected some meat, fat, and bone parameters. Higher phytase dosages did not improve the pigs’ performance, but only increased calcium deposition in their bones.AbstractThis study aims to determine how different doses of phytase in diets including extruded soya and lupine seeds affect fatteners’ performance, meat quality, bone mineralization, and fatty acid profile. Sixty pigs were divided into three treatment groups. The control group was offered a diet without phytase, whereas the Phy100 and Phy400 groups were provided with 100 g and 400 g of phytase per ton of their diet, respectively. The animals from both experimental groups were characterized by a significantly (p< 0.05) higher body weight gain and lower feed efficiency in the starter period than the control group. Unfortunately, their meat had lower (p< 0.05) fat content, gluteal muscle thickness, and water-holding capacity. In the meat, a higher phosphorus content (p< 0.05) was found, and in the bones, a higher calcium (for Phy400) content was found when phytase was added to the pigs’ diet. The pigs from the Phy100 group tended to have higher mean backfat thickness and C18:2 n-6 content in their fat, but lower C22:5 n-3 content, than the other groups. A higher dosage of phytase is not necessary for the diets of fatteners with extruded full-fat soya and lupin seeds.