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Cage-reared, egg-type domestic pullets were given a 7L:17D regimen from 2 d of age. At eight weeks, 24 birds were transferred to individual cages in each of four controlled environment chambers and maintained on 7-h photoperiods. A radio was played at 75-80 dB from 10 weeks of age in two of the chambers during the 7 h immediately preceding the photoperiod, and the other two chambers remained as controls. Mean age at first egg for the radio birds (143 d) was 13 d significantly earlier than controls, but body weight at first egg was similar for the two groups. Although this suggests that the radio noise might have stimulated feeding activity and accelerated growth, there was no significant difference between the groups for a regression of body weight on age at first egg, indicating that accelerated growth did not contribute to the advance in maturity. A shift in the location of the photoinducible phase, so that it became partially illuminated by the normally non-stimulatory 7-h photoperiod, is another possible reason for the earlier sexual development. Plasma melatonin concentrations midway through the 7-h dark period in which the radio was played were similar to those of non-radio controls, indicating that this period was not regarded as being part of a 14-h subjective day.
Keywords: Environmental cue; sound; sexual maturity
South African Journal of Animal Sciences Vol. 35 (3) 2005: pp.180-185