Responses of laying hens to gradual and abrupt increases in ambient temperature and humidity

Abstract

White Leghorn x Australorp laying hens were gradually or abruptly exposed to natural summer climate regimens in which high relative humidities and temperatures in excess of 35¦C were simulated. Food intake, feeding patterns, egg production, egg weight, egg quality and time of oviposition were recorded. Mortality was high when hens were subjected to abrupt increases in ambient temperature but no deaths from heat stress were observed when hens were able to acclimatize to high temperatures. Food intakes were reduced significantly at high temperatures but less marked reductions were observed in egg production. Therefore, food was used more efficiently in heat-stressed hens. Food conversion ratios of heat-stressed and control hens were, respectively, 2.99 and 3.07 (Experiment 1 ), 2.82 and 3.04 (Experiment 2), and 2.09 and 2.45 (Experiment 3) g food/g egg. Heat-stressed hens consumed less food during the hot afternoon period. Extending the daily photoperiod from 16 to 20 h had no beneficial effect on total food intake or egg production. Egg quality, including egg shell thickness, did not deteriorate at high temperatures and this appeared to be related to a high atmospheric concentration of carbon dioxide produced by excessive panting