The Response to Dietary Leucine in Laying Lens

SIMPLE SUMMARY: The requirement of a laying hen for an essential amino acid depends on its body weight, for maintenance, and on its potential egg mass output. The requirement for maintenance is a greater proportion of the total nutrient requirement in laying hens than in growing animals, and for this reason an accurate prediction of the maintenance requirement of laying hens is essential when partitioning the total daily requirement between the two factors. In this study, which was designed to determine the optimum economic intake of SID-Leucine for laying hens, separate trials were used to measure the requirements for maintenance and for egg mass output. The amount of Leu required for egg production (11.6 mg/g egg) suggests an efficiency of utilization of dietary Leu of 0.79. Because the content of Leu is high in maize, this amino acid is unlikely to be limiting in laying hen feeds in which maize is used as the main cereal. ABSTRACT: This study aimed to estimate the standardized ileal digestible leucine intake (SID-Leu(i), mg) in laying hens for maintenance, and to describe the response in laying hens to SID-Leu(i), thereby providing the information required to determine the optimum economic intake of SID-Leu for laying hens. Two nitrogen balance series, one balanced and the other unbalanced with respect to leucine (Leu), were used to estimate the SID-Leu requirement for maintenance using 36 roosters per series. The roosters were randomly distributed among the six levels of Leu with each level being replicated six times. The six diets were formulated to contain 0.0, 3.5, 6.9, 10.4, 13.9, or 17.4 g/kg of SID-Leu for the unbalanced series and 0.0, 4.0, 8.0, 12.0, 16.0, or 20.0 g/kg of SID-Leu for the balanced series. The SID-Leu(i) maintenance requirement was calculated as 144 mg/bird d, 66 mg/kg d, 74 mg/kg(0.75)d or 395 mg/BP(m)(0.73)d. For the response trial, 120 individually caged laying hens (63 weeks old) were randomly distributed among eight treatments with 15 replicates. To estimate the SID-Leu(i) for the population of hens, the Reading Model was fitted to the data using body weight (BW, kg), SID-Leu(i) and egg output (EO, g). The Reading Model calculated the mg SID-Leu(i) = 11.6 EOmax + 43.4 BW. The efficiency of SID-Leu utilization for laying hens was estimated to be 79%.