Effects of β-mannanase expressed by Pichia pastoris in corn–soybean meal diets on broiler performance, nutrient digestibility, energy utilization and immunoglobulin levels

The objectives of this study were to study the influence of β-mannanase supplementation of corn–soybean meal diets on performance, the coefficient of total tract apparent digestibility (CTTAD) of selected diet components, nitrogen corrected apparent metabolizable energy (AMEn) value and immunoglobulin levels of broilers both in the starter (0–3 wk) and grower (3–6 wk) periods. β-Mannanase, origining from Aspergillus sulphureus, was produced by recombinant Pichia pastoris. Three hundred and sixty, 1-d-old broiler chicks were randomly allocated to one of four dietary treatments consisting of a control diet formulated to be adequate in energy and three low-energy diets supplemented with 0, 1 or 2 g/kg β-mannanase. Our results demonstrated that β-mannanase addition (1 and 2 g/kg) improved (P<0.05) average daily gain (ADG) and feed conversion ratio (FCR) from 0 to 6 wk. β-Mannanase supplementation (2 g/kg) led to an increase (P<0.05) in the CTTAD of crude protein and crude fiber at 6 wk of age, and improved (P<0.05) the AMEn at 3 wk and 6 wk of age, compared with the low-energy control. At 3 wk of age, 2 g/kg β-mannanase supplementation decreased (P<0.05) the relative weight (RW) of the liver and intestine. There was also an increase (P<0.05) in amylase and trypsin content in digesta from the small intestine compared with the low-energy control and 1 g/kg β-mannanase supplementation. Moreover, β-mannanase addition (2 g/kg) decreased (P<0.05) the RW of the thymus (3 wk), bursa (3 and 6 wk) as well as serum IgG and IgM concentrations at 3 wk of age. Our results indicate that β-mannanase supplementation could increase the CTTAD of diet components, while the decrease in immunoglobulin levels is suggestive of a down-regulated immune system that might have allowed nutrients to be redirected towards optimum performance.