A. Ilchev, G. Ganchev

Abstract. A balance trial was performed with three groups of Topigs hybrid pigs (n=3). Pigs received complete compound feeds. For the second (control) group digestible amino acid content was according to hybrid’s nutrition standards (as per Guideline for feeding Topigs sows, 2001. Topigs International, BV). Groups I and III received a ration with digestible amino acid content lower or higher by 15%, respectively, compared to controls. Dietary digestible amino acids in rations for Topigs finisher pigs were more than the animals were able to utilize. Therefore, more extensive research for revision of nutrition norms is needed. The reduction of digestible amino acids in feeds by 15% did not have a negative effect on nitrogen retention and improved its utilization by 11.7 % compared to animals fed as per guidelines. The lower digestible amino acid content reduced the nitrogen output with urine by more than 30% (Р<0.05). Water consumption and urine output were directly related to dietary nitrogen concentration. Increasing the content of digestible amino acids resulted in higher levels of these indices. About 63% of dietary nitrogen remained non-utilized and is lost with excreta. The reduction of digestible amino acids in diets by 15% decreased nitrogen output by 6.35 %.