PHENYLALANINE AND TYROSINE REQUIREMENTS O F MULE DUCKLINGS

Growth assays were conducted to determine the dietary phenylalanine an d tyrosine requirements of mule ducklings from 0 to 3 weeks of age and to investigate the phenylalanine-tyrosine interrelationship in duck n utrition. Primary experiment showed no improvement in weight gain and feed efficiency for mule ducklings fed on the practical corn-soy diet containing 18.8% of crude protein and 2856 kcal/kg of metabolizable en ergy with 0.91% phenylalanine and 0.69% tyrosine. Therefore, there was no need to supply additional phenylalanine or tyrosine to the corn-so y based diet in order to obtain maximal weight gain of mule ducklings. Further experiments were designed to lower the content of phenylalani ne and tyrosine in the basal diets for mule ducklings. The requirement for phenylalanine plus tyrosine was obtained by using regression anal ysis on body weight gain or on feed efficiency against phenylalanine p uls tyrosine level in the diet. The results showed that the minimum re quirement of phenylalanine plus tyrosine for mule ducklings was 1.11% of the diet or 5.95% of the dietary protein. In order to investigate t he relationship between two amino acids, graded levels of tyrosine wer e added to the corn-corn starch-amino acid mix basal diet containing d ifferent amounts of phenylalanine. The results showed that as the duck lings were fed on diet deficient seriously in phenylalanine (0.24%), t he addition of tyrosine(0.2-0.8%)could not improve growth performance. When the diets contained marginal levels of phenylalanine (0.44 or 0. 64%), the growth rate was improved as the dietary tyrosine levels (0.3 3-0.73%) in the diets increased indicating that tyrosine could spare t he ducklings requirement for phenylalanine.