A. Ilchev, G. Ganchev

Abstract. A balance trial was performed with 3 groups of three PIC hybrid pigs each fed 3 dietary levels of digestible amino acids – 85 %, 100 % and 115 % of standrd. The control group was fed according to nutrition standards (100 %). The other two groups, received a ration with amino acid content lower or higher by 15%, respectively, compared to controls. The nutrition standards for digestible amino acid content of feeds for the PIC hybrid are perfectly adequate to the needs of animals. They allowed a daily retention of 25 g N and a relatively good utilization of feed protein. The digestible amino acid excess did not improve the nitrogen retention, but only increased its excretion with urine. The water intake and the amount of excreted urine of pigs were directly related to the dietary  nitrogen concentration. They were found to increase parallelly to dietary digestible amino acids content.