Dietary protein reduction with stepwise addition of crystalline amino acids and the effect of considering a minimum glycine-serine content in broiler diets.

Reducing the dependency on soybean meal (SBM) is necessary to improve the sustainability of the poultry industry. Moreover, the recommendations for minimum contents of dietary Gly+Ser require further research. Two parallel studies were executed to determine the effects of replacing SBM with crystalline amino acids (CAA) to meet the amino acid requirements and to determine whether a minimum content of Gly+Ser is necessary for broiler diets. In study 1, 1,860 one-day-old male chicks were fed a common starter phase diet (22.8% CP). During the grower-1, grower-2, and finisher phases, the control CP content was reduced (up to 2.1%) with the stepwise addition of CAA (treatments 1-5). Within each feeding phase, AME, standardized ileal digestible Lys, and the minimum Met, Thr, Val, Gly+Ser, Ile, Arg, and Trp to Lys ratios were similar. In study 2, 1,488 male chickens were used in a 2 × 2 factorial design with the Gly+Ser content and feed ingredients used as main factors. Performance was monitored during 41 d in both studies. Reduction in CP content linearly increased (P < 0.05) BW, ADG, and ADFI in the grower-1, grower-2, and finisher phases. When the overall FCR was adjusted considering the BW differences (FCRadj); FCRadj linearly decreased with the weighted average CP (WACP) content (P < 0.001). In the lowest CP treatment, estimated dietary N utilization efficiency was improved by 10%, and the overall N excretion was reduced by 16% compared with the control (P < 0.001). The overall SBM and soybean oil intakes were linearly reduced relative to WACP (-12.0 and -20.2% in control vs. treatment 5, respectively; P < 0.001). Formulating with a minimum Gly+Ser content in the starter phase improved the FCR (P < 0.05) only in the corn-SBM-based diet. In grower-1, increasing Gly+Ser content improved the FCR independent of the feed ingredients used (P < 0.05). Crystalline amino acids can be used to partially replace intact protein reducing the dependency on SBM. Young birds may not synthesize enough Gly endogenously and a minimum content should be provided in the early phases.

The effect of gradually decreasing the dietary energy content, at constant or increased lysine:energy ratio on broiler performance, carcass yield, and body composition.

Formulating diets with high AME, especially in the grower and finisher phases, hinders the inclusion of alternative ingredients that are usually cheaper and have lower AME. Moreover, as the chicken grows the feed intake capacity is greater and may be able to maintain BW over a wide range of AME. The objective of this study was to evaluate the performance of chickens fed diets with progressive AME reductions, at constant or increased standardized ileal digestible (SID) lysine:AME ratio (Lys:AME). Treatment 1 (control) was formulated following the SID lysine and AME recommendations for a 4-phase feeding program. Treatment 5 was formulated with -4, -8, and -12% AME in the grower-1, grower-2, and finisher phases, respectively, and with the same Lys:AME compared with the control. Treatment 9 had the same AME as treatment 5 but higher SID lysine, increasing the Lys:AME by 1.5, 3.5, and 5.0% compared with treatment 5. In the grower-1, grower-2, and finisher phases, the final 9 dietary treatments were prepared by mixing the control diet with either treatment 5 or 9 at different proportions (75:25, 50:50, or 25:75). All birds were fed the same starter control diet. Treatments were replicated in 10 pens with 31 male chickens each, and the growth performance of birds was monitored for 42 d. Final BW linearly decreased (P < 0.05) when lowering dietary AME, but it followed a positive quadratic response with higher Lys:AME (P < 0.05). Feed intake increased (P < 0.05) with low AME, independently of the Lys:AME; but the linear regression in the feed conversion ratio (FCR) had a lower slope when the Lys:AME increased. At the end of the study, there were no differences in carcass or breast meat yield (P > 0.10). Progressively reducing AME in the last feeding phases may be a viable nutritional strategy to increase the inclusion of alternative ingredients and potentially reduce feeding costs, despite increments in feed intake and FCR. Adjusting the Lys:AME in low AME diets may help maintain the final BW of birds.