Photoperiods for broiler breeder females during the laying period.

Ross 308 broiler breeder females, maintained in litter-floor pens, were reared from 2 d of age on 8-h photoperiods and transferred abruptly to an 11-, 12-, 13-, or 14-h photoperiod at 20 wk of age and at a mean BW of 2.09 kg. Four qualitative dietary treatments were superimposed upon each photoperiodic treatment, but, in the absence of any significant interactions of photoperiod with diet, only photoperiodic means are reported. Age at 50% egg production (ASM) was progressively advanced as photoperiod increased from 11 to 13 h but was similar for 13-h and 14-h birds. Egg production was significantly related to ASM, with peak egg numbers being stimulated by a transfer to 13-h photoperiods. Rate of lay after 48 wk of age declined more rapidly in the 14-h birds than in any of the other groups, suggestive of an earlier onset of adult photorefractoriness. More eggs were laid outside the nest box and more cracked and dirty eggs were produced by birds on 11and 12-h photoperiods than on 13or 14-h photoperiods. Mean egg weight was positively correlated with ASM but negatively related to photoperiod; the number of eggs thought to be doubleyolked was not significantly affected by photoperiod. Total egg mass output was not significantly affected by photoperiod. Birds exposed to 11-h and 12-h photopenods were heavier at 60 wk than birds transferred to 13or 14-h photoperiods. These findings show that a transfer from 8 to 13 h at 20 wk optimizes egg-laying performance in broiler breeder females, especially when they are kept beyond 60 wk of age. [ABSTRACT FROM AUTHOR]