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.