Effect of Avilamycin and Tylosin-phosphate on nitrogen metabolism in piglets at graded levels of dietary protein and supplemented essential amino acids

In a metabolism trial piglets were fed restrictively diets containing 19 %, 17 % or 15 % crude protein with increasing supplementation of crystalline essential amino acids. At each protein level the diets were fortified with nutritive antibiotics as follows: no additive, Avilamycin (40 mg/kg), or Ty losin-phosphate (40 mg/kg). The nitrogen balance was recorded and the urea concentration in blood plasma was measured at the end of the experiment. On average, Avilamycin and Tylosin-phosphate improved the N retention by 4 % while mean urea concentration of blood plasma was not affected. Compared to 19 % dietary protein the average N retention remained unchanged in anima ls fed the 17 % diet but it fell at further reductions to 15 % dietary prot ein by 4 %. The average concentration of urea in blood plasma decreased wit h sinking dietary protein content (24.4 vs. 17.6 vs. 4.9 mg/100 ml). There was no indication of a change in the influence of Avilamycin and Tylo sin-phosphate on N balance at different levels of dietary protein. Obviousl y, the quantity and quality of dietary protein does not exert any relevant influence on the efficacy of Avilamycin and Tylosin-phosphate.