А. Ilchev, G. Gаnchev, S. Chobanova, D. Kanakov, P. Petkov, I. Nikiforov

Five balance feeding trials were performed to evaluate age-related changes in nitrogen, phosphorus and calcium utilization in growing and fattening male castrated DanBred hybrid pigs. Two commercial phytase preparations were used: Optiphos and Natuphos at a dose of 0.01 %. It was found out that with age, the amount of dietary nitrogen intake and nitrogen output in urine increased statistically significantly (P<0,05). The total nitrogen output was also higher. The retention of nitrogen decreased substantially with age. The supplementation of rations with phytase did not alter this tendency. Phytase added to feed improved phosphorus absorption by 28-34 % and reduced its total output by 38-45 %. The digestibility of calcium in pigs decreased with age, whereas its output in faeces became higher. There was no statistically significant difference between the effects of Optiphos and Natuphos