Day-old male layer chicks (G. gallu

Day-old male layer chicks (G. gallus, Julia, Ninobe Hatchery, Kagawa, Japan) were raised in a room kept at 30 C with continuous lighting. A commercial diet (crude protein: 24%, metabolizable energy: 3050 kcal/kg, Toyohashi Feed Mills Co. Ltd., Aichi, Japan) and water were availablead libitumto the chicks. Chicks were transferred to their individual cages 1 day before each experiment. Before the experiment, body weight was measured and then chicks were distributed into experimental groups so that the average body weight was as uniform as possible between treatment groups. The chicks were maintained in accordance with the recommendations of the National Research Council.