Brain and serum galanin, thyroid hormones, and TSH are not influenced by different photoperiod schedules in broiler chickens

The purpose of the present study was to evaluate the effect of three different light regimens on serum thyroid hormones (THs), thyroid-stimulating hormone (TSH), and galanin levels, as well as brain galanin concentration, of broiler chickens. To this end, three groups of 1-day-old Cobb 500 broiler chicks were used. Each group consisted of 20 chickens. The chicks were kept in separate light-proof controlled rooms. All birds were reared on continuous light until 1 week of age. Then, the first group was treated under a continuous lighting (CL) program (23L:1D); the second group treated under a non-intermittent restricted lighting program (NIL) (6L:18D from day 7 to 28, 23L:1D from day 29 to 42); and the third one treated under an intermittent lighting program (IL) (1L:3D cycles). Feed intake per group was recorded during the experiment. At the end of the experiment (42 days of age), the birds were bled. Sera were collected from both fasted and fed chicks of each group and thyroid hormones, TSH, and galanin levels determined. Thereafter, chicks were humanely slaughtered, and the brain was removed for evaluation of galanin levels. Serum T3, T4, and TSH of birds under different photoperiod schedules were not significantly different in both fasted and fed chicks (P > 0.05). T3 levels were significantly lower in fasted as compared with fed chicks in all groups (P < 0.05). However, fasted birds showed significantly higher plasma T4 levels than fed ones in each group (P < 0.05).No significant differences were observed in serum and brain galanin concentrations among different groups, in both the fasted and fed birds (P > 0.05). Serum/brain galanin with thyroid hormones and TSH in all groups were not significantly correlated. In conclusion, serum thyroid hormones, TSH, galanin, and brain galanin were not influenced by CL, NIL, and IL programs in broiler chickens.