Response of YPM x Ross 708 male broilers to diets containing varying inclusions of phytase, calcium butyrate, and bacitracin methylene disalicylate from 1 to 42 d of age-part 1: performance, processing yields, and nutrient digestibility.

This 42-d study evaluated the effects of phytase, calcium butyrate (CB), and bacitracin methylene disalicylate 50 (BMD) on broiler performance, processing yields, and nutrient digestibility. Ross YPM x 708 male broilers (2,880 total) were distributed in 72 floor pens and assigned to 1 of 9 treatments (8 replicates/treatment) on d of hatch. This experiment was a 2 × 4 + 1 factorial arrangement, including 2 phytase concentrations (500 or 1,500 FTU/kg), 4 microbiota modulating feed additive groups (MMFA; none, CB (0.5 g/kg of diet), BMD (55 mg/kg of diet), or both CB and BMD), and a negative control without feed additives. Broiler performance (d 14, 28, and 42), apparent ileal nutrient digestibility (d 28 and 42), and processing yields (d 43) were determined. Day 14 BW increased with BMD inclusion compared to CB and no MMFA in the 1,500 FTU/kg group but BW were similar between all MMFA combined with 500 FTU/kg (P ≤ 0.05). Supplementing BMD increased d 28 BW and reduced d 1 to 28 feed conversion ratio compared to CB and no MMFA (main effect, P ≤ 0.05). Day 42 BW varied depending on dietary phytase concentrations. When diets contained 500 FTU/kg, broilers fed both CB and BMD had a higher BW than broilers fed only CB. Whereas when the inclusion of phytase was increased to 1,500 FTU/kg, broilers fed diets with only BMD or both CB and BMD had higher BW than broilers fed diets with no MMFA (P ≤ 0.05). Phytase concentrations at 1,500 FTU/kg increased (P ≤ 0.05) digestibility of fat (main effect, d 42), phosphorus (d 28 and 42), and apparent ileal digestible energy (main effect, d 42) compared to 500 FTU/kg. In this study, dietary BMD improved broiler growth compared to CB and no MMFA. However, these observed differences between CB and BMD were dependent on dietary phytase concentrations.