THREONINE REQUIREMENT AND THREONINE IMBALANCE IN BROILER-CHICKENS

Three experiments were conducted to determine the effect of excess die tary protein on threonine requirement of broiler chicks to 14 d of age (Experiments 1 and 2) and to determine the threonine requirement from 16 to 28 d of age (Experiment 3). Two dietary protein levels were use d in Experiments 1 and 2: 20% CP in a threonine-limiting basal diet co ntaining wheat, peanut meal, and selected amino acids and 25% CP in th e same basal diet supplemented with a mixture of amino acids lacking t hreonine. A threonine-limiting 25% CP diet based on corn, soybean meal , and amino acids was also included in Experiment 2. The threonine req uirement of chicks from 16 to 28 d of age was determined using a singl e CP level (20%) in Experiment 3. Threonine requirements were estimate d by broken line regression analysis of weight gain and feed efficienc y. Threonine requirements based on weight gain were 7.7 and 6.7 g/kg o f diet in Experiments 1 and 2, respectively, for chicks receiving the 20% CP diets. The requirements increased to 8.6 and 8.2 g/kg, respecti vely, for chicks fed the 25% CP diets based on wheat, peanut meal, and amino acids. The requirement for maximum weight gain of chicks fed 25 % CP based on com, soybean meal, and amino acids was 7.7 g/kg of diet. However, chicks ate more of this diet, and on an intake basis, the re quirement of the chicks fed the 25% CP diets based on wheat and peanut meal or com and soybean meal did not differ. Requirements based on fe ed efficiency were equal to, or less than, those based on weight gain in Experiments 1 and 2. Body moisture and fat contents were affected b y dietary CP level (P < .01), ingredient composition (P < .01), and th reonine content (P < .05). Estimates of threonine requirements based o n regression analysis of plasma threonine concentrations were higher t han those based on weight gain or feed efficiency. The threonine requi rements of chicks fed a 20% CP diet from 16 to 28 d of age were 6.3 an d 6.9 g/kg of diet based on weight gain and feed efficiency, respectiv ely.