Lack of response of laying hens to relative humidity at high ambient temperature

1. The effects of relative humidity (rh=40% to 70%) at high ambient tempera ture (T-a) on the performance of laying hens at different ages (8 to 10 mon ths, Trial 1; and 16 to 18 months, Trial 2) was evaluated. Laying hens were exposed to 25 degreesC (control) for 3 weeks and thereafter acclimated for 1 week to 35 degreesC and 4 different rh. 2. Body weight declined significantly in young and older hens exposed to 60 % or 70% and 70% rh, respectively. Food intake declined with increasing T-a , except in the case of older hens exposed to 60% rh, for which it remained relatively constant. Water consumption, however, increased with increasing T-a but the increase was significant in young hens exposed to 70% rh only. 3. Egg production was not affected by the changes in T-a. However, a decrea se in egg production was observed in older hens exposed to 60% rh. 4. Egg weight (EW), shell weight (SW) and shell thickness (ST) were signifi cantly reduced by exposure to elevated T-a, whereas % breakage significantl y increased. In young hens, a response to rh was exhibited in ST which was significantly higher in hens exposed to the low rh (40% to 45%) than in tho se exposed to the highest rh (70% to 75%). 5. It can be concluded that T-a is the main environmental factor affecting young and older laying hens while the effect of rh is minor.