Thermal stability of multi-tier layer hen housing with all-year sidewall inlet ventilation system

Large temperature fluctuations in alternative hen housing threaten poultry welfare and productivity because of temporary and seasonal ventilation adjustments. This study proposes an all-year sidewall inlet ventilation (ASV) system with buffer spaces and constant air inlet to stabilize the incoming airflow and minimize thermal variations at the hen level. The ASV system was evaluated in a commercial multi-tier layer house housing 24,000 hens in a temperate monsoon climate. Over 407 days, 58 sensors monitored outdoor conditions, buffer spaces, sidewall inlets, and indoor zones (between/within colony rows), with egg production and feed intake recorded. Results indicated without supplementary heating, indoor air temperatures ranged from 18.3 to 29.8°C, while outdoor temperature fluctuated from -22.0 to 37.3°C. The diurnal temperature fluctuation indoors remained within 3°C for 77.4 % of the period, peaking at 4.7°C. Average diurnal fluctuations indoors were 2.4°C (winter), 2.0°C (transition season), and 2.8°C (summer), compared to outdoors at 12.9°C, 14.0°C, and 11.6°C, respectively. During a 21.9°C outdoor diurnal fluctuation, variations in buffer spaces, sidewall inlets, and indoors measured 17.7°C, 12.2°C, and 4.7°C, showing significant gradation (P < 0.05). Summer indoor temperatures exceeded 26°C on 112 days due to cooling-activation at 28.0°C and reduced buffer space residence times. In the hottest month, interstitial zones between colony rows averaged 26.5 ± 1.29°C and 80 % ± 4.5 % RH. Microclimates within colony rows exhibited 1.5°C warmer and 9 % lower in RH than interstitial spaces (P < 0.05). Longitudinal temperature gradients peaked at the rear section, whereas lateral distributions were symmetric, with the middle column 0.7°C cooler than sides (P < 0.05). Diurnal feed intake deviation from the theoretical curve strongly correlated with 7-day mean, maximum, and minimum indoor temperatures (P < 0.001). In summary, the ASV system maintained indoor diurnal temperature fluctuation within 4.7°C across season, providing an effective ventilation strategy to support the transition to cage-free systems.