Defining optimal dietary starch, oil, and amino acid inclusion levels for broilers experiencing a coccidiosis challenge

Alternative methods to alleviate coccidi-osis in broilers are of interest to producers, including die-tary strategies to minimize disruptions in growth rate and efficiency when faced with health challenges. Our objective was to determine optimal combinations of die-tary starch, amino acids (AA), and oil to benefit pro-ductivity of broilers experiencing Eimeria-induced immune activation. Two trials were conducted using 1,536 male Ross 308 broiler chicks in floor pens ran-domly assigned to 1 of 17 experimental treatments. All birds received common starter (d 0-10) and finisher (d 24-35) diets, and only differed based on their assigned experimental grower diet (d 10-24). Trial 1 experimen-tal grower diets ranged from 2,700 to 3,300 kcal/kg AME. Trial 2 included 10 experimental grower diets fol-lowing a simplex lattice design consisting of 3 basal lots formulated to have the highest starch (45.4%), oil (10.2%), or AA density (120, 1.33% digestible Lys) and mixed in 4 equally spaced levels for each component (0, 0.33, 0.67, 1). These mixtures enabled varying densities of AA (80-120% of recommendation), starch:oil (4:1 -20:1), and AME (2,940-3,450 kcal/kg). Bird and feeder weights were collected on d 0, 10, 24, and 35, and birds were exposed to an Eimeria challenge on d 11 or 12. In trial 2, excreta samples were collected for AME determination and carcasses were processed on d 36. Data were analyzed using ANOVA, t test, or regression. In Trial 1, BW gain and feed conversion were improved (P < 0.05) by increasing dietary AME. In Trial 2, birds receiving diets containing AA at 93 to 107% of recommendations and higher oil exhibited improved (P < 0.05) performance, but increased starch at the expense of oil reduced performance (P < 0.05). Relative breast and fat pad weights were not influenced by diet in Trial 2. We determined that broilers mildly challenged with Eimeria would exhibit highest BW gain when receiving diets containing 35.8% starch, 8.9% oil, and 101.3% of AA recommendations, which can be utilized by producers to maintain productivity under health-challenged conditions.