Photoperiod, adrenal corticosterone and the development of avian glaucoma

Three hundred and fifty Rhode Island Red cockerels were maintained under three lighting conditions from day one after hatching to 10 weeks of age to investigate the possible relationships between photoperiod, avian glaucoma and adrenal function. Other parameters studied included body, comb, testicular and thyroid weights. The lighting treatments included (1) diurnal light/dark or 12L:12D, (2) continuous light or 24L:0D, and (3) continuous dark or 0L:24D.

Both 24L:0D and 0L:24D conditions significantly increased avian eyeball weight, adrenal weight and plasma content of corticosterone compared with the 12L:12D regimen (P > 0.05). There was a highly significant reduction in eye depth (P < 0.01) when birds were raised under continuous light or continuous darkness. A non-significant reduction in thyroid weight was produced by keeping chicks under total illumination and also under 24 hours of darkness. Constant light greatly enhanced testicular growth while the continuous absence of light drastically reduced testes weight in comparison with testicular growth under alternating light and dark.

Body weight, comb weight, and intraocular pressure were not significantly affected by any of the treatments.

At least two peaks of plasma corticosterone were seen under each treatment, but the corticosterone diurnal rhythm was not disturbed even though the levels of the hormone were increased significantly (P < 0.05) by the absence of an alternating light and dark treatment.