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Assessment of the Nitrogen Correction Factor in Evaluating Metabolizable Energy of Corn and Soybean Meal in Diets for Broilers

Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada, N1G 2W1

¹ Corresponding author: sleeson{at}uoguelph.ca

Three experiments were carried out to determine AME and AME_n of corn and soybean meal (SMB) in diets for growing broilers. In experiments 1 and 2, ingredient-specific basal diets or a combination of these basal diets with corn and SBM were prepared. For corn, the substitution was 25, 50, or 75% of the total diet, whereas SBM substitution was at 10, 20, or 30%. In experiment 1, birds were fed the experimental diets continuously from 0 to 33 d, and AME and AME_n were determined during 9 to 12 d and 30 to 33 d of age. In experiment 2, birds were fed the experimental diets only around the time of the collection period. The AME_n of corn was 95 to 97% of corresponding AME, whereas for SBM, AME_n was 93 to 88% of AME. Linear regression was used as an alternative method of calculating ingredient energy values resulting in a significant regression of diet AME and AME_n content on inclusion level, for each period of time and for each ingredient (corn and SBM). Based on varying inclusion levels of test ingredients in the diet, the extrapolated AME and AME_n of corn were estimated more precisely (R² = 0.90 to 0.95) than those of SBM (R² = 0.57 to 0.85), suggesting that the variability of AME and AME_n is better explained by a linear regression of AME or AME_n on percentage of inclusion. For corn, AME and AME_n were little affected by age, and the effect of N correction was consistent at around 3%. Determined energy values of SBM were more variable. Experiment 3 was conducted to assess the effect of formulating diets based on either AME or AME_n on broiler performance. A 2-sample t-test was implemented examining AME vs. AME_n formulation. The analyses for numerous production and carcass traits were nonsignificant except for the case of less abdominal fat in birds fed diets formulated to AME rather than AME_n (P < 0.01). These results showed that the use of the N correction imposed a penalty to corn of 3 to 5% and SBM of 7 to 12%.

Key Words: metabolizable energy • ingredient • broiler