Evaluating the Effects of Exogenous Enzyme Supplementation on Broiler Growth

Experiments were conducted to investigate the effects of exogenous enzymes in poultry diets. In Chapter 4, a study was conducted to determine the effects of a corn-expressed recombinant carbohydrase (AC1) on broiler performance and digesta viscosity in high non-starch polysaccharide (NSP) diets through 21 days of age. One day-old Hubbard × Cobb 500 chicks were assigned to 6 dietary treatments. Each treatment consisted of 12 replicate pens of 10 birds. The positive control diet (PC) was a corn and soybean meal formulation. The negative control diet (NC) included 10% wheat and 10% corn distiller’s dried grains with solubles (DDGS). The NC contained 100 kcal/kg less ME than the PC. Increasing inclusions of AC1 were applied to the NC to contain 50, 100, 200, and 400 U β-glucanase (β-Glu-U) per kg of feed. Preliminary experiments demonstrated AC1 homogeneity and stability post pelleting. Live weight gain (LWG) was the highest for PC fed birds from 1 to 14 d; however, birds fed NC with 400 β-Glu-U/kg also had similar LWG as the PC. Feed conversion ratio (FCR) from d 1 to 21 was lowest for PC fed birds; however, birds fed NC with 400 β-Glu-U/kg also had similar FCR as PC. Birds fed NC had lower LWG and higher viscosity than birds fed PC on day 14, but not on day 21. However, birds supplemented with 200 or 400 β-Glu-U/kg had similar 14 d digesta viscosity as birds fed PC. These data indicate that NSP ingredients may have a greater impact on digesta viscosity early in broiler growth and that AC1 at 200 and 400 β-Glu-U/kg produced similar results to PC. A second study was then conducted (Chapter 2) to further investigate the effects of AC1 on dietary and intestinal viscosity and broiler performance when included in a high NSP diet. Nine hundred sixty, Hubbard x Ross 708, day-old, male broiler chicks were fed one of eight dietary treatments for 21d. Diets included a corn-soybean meal based diet (PC_1) and a diet of similar essential nutrient density, but with a 10% inclusion of both wheat and DDGS (PC_2) and a negative control (NC) with similar ingredients as PC_2, but with ME reduced by 125 kcal/kg. Additional treatments had varying levels of AC1, supplying 50, 100, 200, 400, or 600 U βGlucanase (β-Glu-U) per kg of feed, mixed into the NC diet. Dietary and digesta (d14) viscosity and weekly bird performance were measured. The inclusion of AC1 at 50-400 β-Glu-U/kg reduced FCR equivalent to PC_1. The results also showed that intestinal viscosity was correlated to d1-21 FCR and inversely correlated to d1-21 LWG. This study demonstrates that AC1 can reduce intestinal viscosity and improve early FCR in birds fed high viscosity diets and that an in vitro viscosity assay may be used to predict in vivo response. In Chapter 3, a study was conducted to determine digestible amino acid concentrations and broiler performance of diets that vary in amino acid concentration and enzyme inclusion. Treatments included a PC (100% amino acid recommendations), NC (85% amino acid recommendations), and six additional diets containing commercially available enzyme supplements (Single Dose Phytase, Super Dose Phytase, Single Dose NSPase, Super Dose Phytase + Single Dose NSPase, Protease 1, and Protease 2) added to the NC based on manufacturers’ recommendations. Diets were conditioned at 70°C and fed as crumbles to Hubbard x Ross 708 broiler chicks for 22d. Feeding NC with the inclusion of phytase, independent of dose or combination with the NSPase, and Protease 1 produced d22 feed conversion ratio similar to the PC. When feeding NC with the single dose NSPase, Protease 1, or Protease 2 d22 LWG was not comparable to the PC. These data suggest that the addition of phytase to an amino acid deficient diet can improve broiler performance.