Animal Biology 65 (2015) 13–20 brill.com/ab Seasons induce changes in the daily rhythm of plasma melatonin in goats (Capra hircus) Vincenzo Carcangiu 1 , Claudia Giannetto 2 , Sebastiano Luridiana 1 , Francesco Fazio 2 , Maria Consuelo Mura 1 , Albamaria Parmeggiani 3 and Giuseppe Piccione 2,∗ 1 Department of Veterinary Sciences, University of Sassari, Via Vienna 2, 07100 Sassari, Italy 2 Department of Veterinary Sciences, University of Messina, Polo Universitario dell’Annunziata, 98168 Messina, Italy 3 Department of Veterinary Sciences, University of Bologna, Via Tolara di Sopra 50, 40064 Ozzano Emilia, Bologna, Italy Submitted: July 24, 2014. Final revision received: November 19, 2014. Accepted: November 26, 2014 Abstract To evaluate the influence of natural photoperiod on the daily rhythm of melatonin, we assessed mela- tonin plasma concentration at four different times of the year. Ten Sarda breed goats were led to the natural pasture during the day and were kept in a common stall during the night. Blood samples were collected by means of a cannula inserted into the jugular vein, every two hours for a 24-hour period during the vernal equinox, summer solstice, autumn equinox, and winter solstice. Our results showed the existence of clear seasonal variation in the daily rhythm of plasma melatonin in goats, with the highest MESOR value in winter followed by spring. Acrophase was always observed in the middle of the scotophase. Robustness of the rhythm was higher in the spring as compared to the winter. Our re- sults showed a daily rhythm of plasma melatonin concentration strongly related to the seasons. These results could be useful to establish appropriately timed melatonin and/or photoperiod treatments for the management of reproductive physiology in goats. Keywords Daily rhythm; environmental condition; goats; melatonin Introduction The annual variation in day length remarkably influences the secretion of many hormones. The pacemaker in the suprachiasmatic nucleus (SCN) is entrained to the ∗) Corresponding author; e-mail: gpiccione@unime.it  Koninklijke Brill NV, Leiden, 2015 DOI 10.1163/15707563-00002456