Effects of photoperiod and pinealectomy on domestic chickens

A series of investigations was undertaken to study the relationship between the photoperiod, the pineal gland and various physiological attributes of domestic chickens. Live body, comb, eye, testis and pineal weights were determined at the end of the trials as well as eye depth, intra ocular pressure and osmolality. Birds maintained under constant dark conditions were heavier, though not significantly, at 10 weeks of age, than those kept in constant light or 12L:12D, Pinealectomised birds were only slightly lower in weight than birds with intact pineals (P< 0.05). Combs were more supple and heavier if birds were reared under 12L:12D. Eye weight was depressed in the presence of the pineal gland but increased in either 24 hour darkness or 24 hour light. Testis weight was significantly (P<0.05) reduced in the birds with functional pineals, and a similar decline occurred when chicks were subjected to 24 hours of darkness. Eye pressures as well as ocular osmolalities were not significantly affected by either the photoperiod or the pineal gland, although birds kept under 24 hour light or darkness developed varying degrees of glaucoma. Shifting birds from one photoperiod to another at 5 weeks of age had varying effects on measured parameters. Although the pineal gland was adversely affected by shifting or constant photoperiods, the effects were not statistically significant.