Abstract

1. Laying hens when transferred from accommodation at an ambient temperature (Ta) of 30 °C to one of 20 °C failed to acclimatise to intermittent heat stress (Ta 38 °C) commencing one day after the transfer.

2. After 21 d of intermittent exposure to 38 °C these hens showed little or no increase in heat tolerance, whereas hens living constantly at either Ta 20 °C or 30 °C acclimatised normally.

3. The failure to acclimatise was also observed when hens were transferred from Ta 30 °C to 5 °C but not when transferred from Ta 5 °C to 30 °C.

4. The failure to acclimatise following transfer from a warm to a cool environment was accompanied by an increase in food intake; if food intake was not allowed to increase the hens acclimatised normally to heat stress.