Performance and Gut Microbial Profile of Broilers Fed Diets with Varying Levels of Protein and Energy and Supplemented with a Protease Complex

Nutrients in most feed ingredients are present in a complex matrix. Therefore, it is anticipated that feed enzymes like protease can exert a wide influence on nutrient digestibility beyond their targeted substrates (Cowieson and Bedford, 2009). For instance, the disruption of protein matrix surrounding starch granules due to protease supplementation had been shown to improve energy digestibility in some cereal grains (McAllister et al., 1993). It is hypothesised that protease may benefit broiler performance through improved nutrient digestibility and its concomitant impact on gut microbial profile through substrate availability modifications in the gastrointestinal tract.

A total of 720-one-day-old male broilers (Vencobb 430) were fed for 42 days with either a standard diet or with diets reduced in digestible amino acids (AAs) by 5% and metabolizable energy (ME) by 0.2092 MJ/kg. Both diets were then supplemented with a protease complex. Protease was included at 0, 125, and 200 mg/kg diet. A completely randomized block design with 2 levels of dietary AA (100% or 95% of the standard diet), 2 levels of ME (100% or -0.2092 MJ/kg of the standard diet), and 3 levels of protease (0, 125, or 200 mg/kg diet) in a 2 x 2 x 3 factorial arrangement was used. Data were subjected to ANOVA using a GLM and a polynomial contrast to determine the linearity of dose response to protease. At 42 d, the main effects of dietary AA and ME levels decreased and increased (P < 0.05) ADG and FCR, respectively, in broilers fed reduced AA (67.9 vs. 69.6 g and 1.678 vs. 1.640) or ME (67. 8 vs. 69.6 g and 1.691 vs. 1.628) compared to those fed standard diet. On the other hand, the main effect of protease supplementation (0, 125, 200 mg/kg diet) increased ADG (67.7 vs. 69.2 vs. 69.3 g) and tended to improve FCR (1.676 vs. 1.654 vs. 1.649; P < 0.07) in a dose dependent linear manner. In terms of gut microbial profile (log₁₀ CFU/g), broilers fed reduced dietary AA had increased (P < 0.05) ileal Escherichia coli (7.83 vs. 7.36), Salmonella spp. (2.17 vs. 2.05) and Clostridium perfringens (7.00 vs. 6.38), and decreased Lactobacillus spp. (7.04 vs. 7.08) compared to those fed standard diet. A similar trend was observed in all bacterial species for broilers fed reduced dietary ME, except for Lactobacillus which was increased compared to the standard group. Protease supplementation decreased the counts of all four bacterial species. The nutritional requirements of different bacteria are known to be speciesdependent and these could have influenced the observed profile in the gut microbiota. In the reduced AA diet, soybean meal and oil sources were partially replaced by corn and therefore, its starch level was increased in relation to protein. On the other hand, in the reduced ME diet, oil sources were also partially replaced by corn leading to increased dietary starch level in proportion to lipid, while AA levels were maintained. Overall, performance of broilers was negatively affected by reduced dietary nutrient density. Protease supplementation on either standard or nutrient reduced diets improved animal performance and appears to offer benefits with respect to gut health through a reduction in numbers of potential pathogens.