This experiment evaluated responses of broilers under different coccidiosis control programs when fed elevated amino acid (AA) concentrations achieved with increased dietary soybean meal (SBM) or feed-grade essential AA. Ross 708 male chicks were allocated in a 2×4 factorial design (24 birds/pen, 12 replicate pens/treatment) with 2 coccidia control methods (1x live vaccine dose or in-feed zoalene) and 4 experimental diets fed during the starter (012 d) and grower (12-26 d) periods: 1) a control diet (CTL), 2) an increased AA density diet containing increased SBM (H-SBM), 3) an increased AA density diet containing CTL-level SBM but increased feed-grade Met, Lys, Thr, Val, Ile, and Arg (H-FG), or 4) the CTL with only Thr, Val, and Arg increased by feed-grade sources to the same levels as the H-SBM and H-FG diets (CTL). Digestible Lys was 1.24 and 1.11% for the CTL diet and increased in the H-SBM and H-FG diets by 6 and 7% in the starter and grower phases, respectively, with other digestible AA/Lys ratios at or above breeder specifications. Common diets were fed during the finisher 1 (26-33 d) and 2 (33-40 d) phases. Feed intake (FI), BW gain (BWG), and FCR were measured during each phase, and fecal oocysts were counted at d 12 and 26. Intestinal segment length and weight were assessed at d 12. At d 40, 6 birds/pen were randomly selected for processing. Data were analyzed by a 2-way ANOVA and means separated by Tukey’s test (P≤0.05). No interactions (P>0.05) between coccidia control method and diet were observed. At d 12, oocyst counts and intestinal length and weight were increased (P<0.001) with vaccination, with no diet effect. From d 0-26, vaccination impaired (P<0.001) BWG and FCR (1.19 vs. 1.22) compared with zoalene, but FI (P>0.05) was unaffected. Broiler BWG and FCR were better (P<0.001) for the H-SBM and H-FG groups compared with the CTL and CTL+ groups. Broiler FI was similar (P<0.001) among the CTL, H-SBM, and H-FG groups but reduced with CTL+. From d 0-40, FCR, but not FI or BWG, was impaired (P<0.001; 1.55 vs. 1.56) by vaccination compared with zoalene. Broiler FI (P<0.001) was highest for H-SBM and H-FG, moderate for CTL, and lowest for CTL+. Birds fed the H-SBM and H-FG diet had improved (P<0.001) BWG and FCR compared to those fed CTL and CTL+. Coccidia control method did not affect (P>0.05) deboned parts yields. Breast meat yield (P<0.001) was greater for the H-SBM and H-FG groups than for the CTL and CTL+ groups.
In conclusion, performance and yield of broilers given a vaccine or in-feed zoalene benefited from increased dietary essential AA regardless of source (SBM or feed-grade AA). However, these benefits were not observed when only ratios of Thr, Val, and Arg were increased.