ORIGINAL ARTICLE Brain and serum galanin, thyroid hormones, and TSH are not influenced by different photoperiod schedules in broiler chickens Najmeh Mosleh 1,2 & Saeed Nazifi 1 & Marzieh Zakeri 3 Received: 2 May 2015 /Accepted: 21 July 2015 /Published online: 31 July 2015 # Springer-Verlag London 2015 Abstract 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 broil- er 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 con- trolled rooms. All birds were reared on continuous light until 1 week of age. Then, the first group was treated under a con- tinuous 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 re- corded 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 hor- mones, TSH, and galanin levels determined. Thereafter, chicks were humanely slaughtered, and the brain was re- moved 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 ob- served in serum and brain galanin concentrations among dif- ferent 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. Keywords Galanin . Thyroid hormones . Photoperiod schedules . Chicken Introduction Restricted lighting programs have received considerable at- tention as a management tool in broiler production to improve body weight, feed conversion ratio (FCR), as well as immune status and health (Olanrewaju et al. 2006). Effects of different light regimens on performance and disease control of broilers have been clearly described by previous researchers (Mahmud et al. 2011). Moreover, an intermittent lighting program re- duces feed intake in broilers (Buyse et al. 1996). Regulation of feed intake is complex and is influenced by several factors including circulatory hormones (Richards and Proszkowiec- Weglarz 2007; Husvéth 2011). Light has an important role in determining secretion patterns of several hormones that are involved in growth, maturation, and reproduction (Olanrewaju et al. 2006). One of the metabolic hormones which seems to play a role in regulation of feed intake in chickens is galanin. Galanin, a 29-amino acid peptide, was initially isolated from porcine intestine extract (Tatemoto et al. 1983) and has been shown to have a wide distribution in the central nervous system and periphery (Bartfai et al. 1993). Avian galanin was first isolated from chicken intestine (Norberg et al. 1991) and subsequently from different tissues * Saeed Nazifi nazifi@shirazu.ac.ir 1 Department of Clinical Studies, School of Veterinary Medicine, Shiraz University, P.O. Box: 1731-71345, Shiraz, Iran 2 Avian Diseases Research Center, School of Veterinary Medicine, Shiraz University, Shiraz, Iran 3 School of Veterinary Medicine, Shiraz University, Shiraz, Iran Comp Clin Pathol (2016) 25:183–188 DOI 10.1007/s00580-015-2166-0