Interactions of dietary protein and threonine on growth performance in Pekin ducklings from 1 to 14 days of age

The present study was conducted to investigate the effects of dietary crude protein (CP) on threonine requirements by determining the interactions of dietary CP levels (16.0, 17.5, 19.0, 20.5, and 22.0%) and supplemental threonine levels (0, 0.07, 0.14, 0.21, and 0.28%) on growth performance of Pekin ducks from 1 to 14 days of age. A total of 1,200 one-day-old male Pekin ducks was randomly allotted to 1 of 25 dietary treatments with 6 replicate pens of 8 birds per pen for each treatment. The results showed that dietary CP and threonine levels affected the average daily feed intake (ADFI, P < 0.0001), average daily gain (ADG, P < 0.0001), ratio of feed/gain (F/G, P < 0.0001) of Pekin ducks, and had an interactions on the ADFI, ADG, F/G (P < 0.0001). The ADG was increased linearly (P < 0.002) and then reached a plateau as the dietary threonine increased at all CP diets. According to the estimation of broken-line models, the dietary threonine requirements at 16.0, 17.5, 19.0, 20.5, and 22.0% CP diets for optimal ADG of ducks were 0.56, 0.61, 0.60, 0.63, and 0.67% when expressed as percentage of diet, or 44.22, 47.65, 47.50, 48.30, and 50.39% when expressed as percentage of dietary lysine, or 3.45, 3.44, 3.12, 3.27, and 2.98% when expressed as percentage of dietary CP, respectively. Threonine requirements of Pekin ducks from 1 to 14 days of age were affected by dietary CP levels according to the Student t test results, but had no difference among the moderate CP level diets (17.5, 19, and 20.5%) when expressed as a percentage of diet or dietary lysine. It was concluded that dietary CP levels affected the threonine requirements of Pekin ducks from 1 to 14 days of age, but threonine requirements were constant within the limiting CP level range (17.5 to 20.5%) with a good balance of dietary amino acid, and were approximately 0.60 to 0.63% of diet or 47.5 to 48.3% of dietary lysine.