Formulating broiler starter diets incorporates specialty highly digestible protein feedstuffs (SPF) in partial replacement of soybean meal (SBM) and antibiotic growth promoters (AGP) in alignment with immature digestive capacity. There is limited comparative data on the effectiveness of SPF on lifetime growth performance, gastrointestinal function and metabolism. Experiments were conducted to assess impacts of 4 SPF (enzyme treated soybean meal, soy protein concentrate, pork meal, and black soldier fly larvae meal) in starter on these parameters. Six starter diets included SPF to compare to SBM, and SBM + AGP, as the controls, were followed by common diet to 49 days. Metabolism and intestinal ecology effects of SPF and AGP in starter were transient, and partial replacement of SBM with SPF was commensurate to AGP in bolstering growth in starter phase, resulting in heavier market weights.