Effects of reduced-protein diets supplemented with protease in broiler chickens under high stocking density

Abstract

The effects of protease supplementation on productive performance and physiological responses were investigated in broiler chickens fed reduced crude-protein (low-CP) diets and reared under normal or high stocking densities (SD). Chicks were housed in pens with two stocking densities (≈10 birds/m2 or ≈15 birds/m2) and fed diets with either the recommended or reduced level of CP and metabolisable energy (ME) from 1 to 21 days. From 22 to 42 days, an equal number of birds from each dietary group was fed one of the following finisher diets: (1) recommended-CP and ME, (2) low-CP and recommended-ME or (3) low-CP and recommended-ME supplemented with protease. No interactions (P > 0.05) were observed between diet and SD for feed intake (FI), weight gain (WG), feed conversion ratio (FCR), Newcastle disease antibody titre, pododermatitis, caecal clostridia, Escherichia coli, lactobacilli, serum corticosterone or acute-phase proteins. Diet had no effect (P > 0.05) on FI, WG or FCR during the finisher period nor on FI and WG during the overall (1–42 days) period. High SD resulted in lower FI (P < 0.05) and Newcastle disease antibody titre (P < 0.05) and higher FCR (P < 0.05), pododermatitis incidence (P < 0.05), caecal population of clostridia (P < 0.05) and E. Coli (P < 0.05), and acute-phase protein and corticosterone concentrations than did normal SD. In conclusion, the supplementation of protease to a low-CP diet during the finisher period had no effect on the performance and immunity of overcrowded broiler chickens. Regardless of dietary CP and protease supplementation, a high SD negatively affected the growth performance, immunity, caecal microflora and welfare of the broiler chickens.