THE BIOEFFICACY OF ZINC BACITRACIN IN PRACTICAL DIETS FOR BROILERS AND LAYING HENS

Two balance trials were conducted to examine the response in metaboliz able energy and metabolizability of both fat and amino acids to graded levels of zinc bacitracin (ZnB; Albac(R) registered trade name of Alp harma, Oslo, Norway) in practical broiler and layer diets varying in t heir nutrient density. Broiler diets were supplemented with either 0, 20, or 50 mg ZnB/kg and layer diets were supplemented with either 0, 5 0, or 100 mg ZnB/kg. Each experimental diet was fed to five replicates of four broiler chicks each or nine replicates of individually housed laying hens, respectively. All balance parameters were significantly influenced by nutrient density, age, and dietary ZnB level. No signifi cant interactions between ZnB by nutrient density were found. Addition of ZnB resulted in a lower excreta:feed ratio and an improved N reten tion; there was a nearly linear relationship between these effects and dietary ZnB levels. Moreover, dietary MEn content was linearly enhanc ed by ZnB supplementation. As a consequence, the bioefficacy of ZnB ca n be expressed in terms of MEn units: the average MEn equivalency of Z nB was 2,080 and 1,184 Mcal/kg, for broiler chicks and laying hens, re spectively.