Relevance of Nitrogen Correction for Assessment of Metabolizable Energy with Broilers to Forty-Nine Days of Age

An experiment was conducted to reevaluate the concept of using AME vs. AME n values for broiler diets. Growing male broilers and adult Leghorn roosters were fed either a single standard diet from 0 to 49 d or a series of starter (0 to 21 d), grower (21 to 35 d), and finisher (35 to 49 d) diets. Apparent ME and AME n were determined during 4 to 7, 11 to 14, 18 to 21, 25 to 28, 32 to 35, 39 to 42, and 46 to 49 d of age. Using the single diet after 7 d, the broiler consistently derives higher AME than do roosters. This same effect was seen with the multiple diet series for broilers. However when N correction is applied, the converse situation is seen, in that roosters consistently attain higher AME n than do broilers at any given age. Using a single diet, rooster AME and AME n values were unaffected by time, whereas broilers exhibit a quadratic relationship for both AME and AME n through 49 d. Nitrogen retention of roosters was rarely different from zero (P > 0.05). For broilers, there was a significant (P < 0.01) increase in grams of N retained each day over time, although when expressed as a percentage of N intake, there was decline over time, especially after 28 d of age. The N correction imposes a 4 to 5% reduction on the AME value of a single diet. When a commercial series of diets was used, the correction declined from 5.3% at 7 d to 3.8% at 49 d, reflecting the decline in protein content of the diet and the decline in N retention over time. This information suggests that if AME rather than AME n values are accepted, then roosters provide a good estimate of values applicable for broiler nutrition, because values are little different. Because there was less variance in energy values expressed as AME n rather than AME, it appears that there was sufficient bird-to-bird variation in growth, N retention, or both, to warrant the use of the correction factor.