Evaluation of the required level of L-threonine amino acid in the diet of Gilan native ducks up to the age of 7 weeks

This study aimed to evaluate the optimal level of threonine in the dietary of Gilan native ducks (mallard) from hatching up to seven weeks of age. Three hundred male Gilan native ducklings, with an average initial weight of 40 g, were randomly assigned to five dietary treatments with six replicates per treatment and ten ducks per replicate in a completely randomized design. The experimental period lasted seven weeks. Ducks were fed with diets containing 0.60, 0.65, 0.70, 0.80, and 0.85 percent of the threonine from 1 to 14 days of age and 0.60, 0.65, 0.70, 0.80, and 0.85 percent of threonine from 15 to 49 days of age. The results indicated that body weight gain, feed intake, and feed conversion ratio initially improved and subsequently declined with increasing dietary threonine levels. The 0.85% threonine resulted in the lowest feed intake, feed conversion ratio, and body weight gain (p<0.05). Thigh and wing weights were highest at the 0.85% dietary threonine level (p<0.05). Nevertheless, increasing dietary threonine significantly elevated monocyte counts, red blood cell volume (MCV), and superoxide dismutase activity (p<0.05). In conclusion, NRC-recommended threonine levels are appropriate for optimal growth performance in Gilan native ducks (mallard), and a 0.85% dietary threonine level exerts positive effects on functional, biochemical, antioxidant, digestive, carcass traits, blood parameters, and intestinal morphology in these ducks.