The experiment was conducted from May to July, 2011, at a farm located near Taka Pass (alt. 722 m) in Tarumizu, Kagoshima Prefecture, which has been consistently affected by FPD. The farm consisted of four windowless, poultry houses arranged in a row. Each house (825 m2/house) contained 18,500 chicks on regular litter (litter moisture varied from 30.9% to 56.5%; referred to as “wet-litter” in this study). In the wet-litter house, water was sprayed onto the floor surface as necessary (1–3 times/week, until 35 days of age; 9 times in total) to maintain the humidity and to prevent dust in the air of the house. Litter was turned as necessary (1–3 times/week) until 28 days of age. The water spray and litter treatment were done routinely according to the management manual of the farm. One of the end houses was used in the present experiment. Adjacent to this end house, an additional windowless poultry house was built to rear another flock of chicks on low-moisture litter (litter moisture varied from 15.1% to 40.0%; referred to as “dry-litter” in this study). This dry-litter house was smaller (14 m2/house), but was designed to operate under conditions identical to the wet-litter house, except for litter condition. In the dry-litter house, water was not sprayed to keep the floor humidity low, and litter was turned frequently (3–4 times/week) until 49 days of age. In both houses, the same sawdust (100%) with a depth of about 10 cm was used as the litter material, and the same compound feed (starter, pre-grower, grower and finisher; Marubeni Nisshin Feed Co., Ltd., Tokyo, Japan) was used in equal amounts. Water supply by nipple drinker, heating by a liquefied petroleum gas system and a vaccination program were also equally given to chicks in both houses.