Evaluation of changes in the concentration of melatonin hormone under the influence of age and season in the Arab Stallion

Various factors, including photoperiod, temperature, nutrition, Body condition and age, are responsible for reproductive behaviors of animals. Environmental, physiological and social factors regulate the onset and sustain of reproductive season. Photoperiod and temperature are key environmental factors, but the first one is more important (Hafez and Hafez 2009). The regulation of reproductive activity by phototherapeutic messages due to secretion of melatonin from the pineal gland in most mammals has been reported, but this relationship is not well known in the horse (Diekman et al., 2002(. Regarding the role of the melatonin hormone in the reproductive process, in this study the aim was to investigate the changes in the concentration of the serum melatonin hormone in the Arab stallion, in three age groups including 2 to 6, 6 to 10 and 10 to 14 years old. The study was conducted under natural photoperiod in the seasons of the summer and winter in the Dezful region.
Material and This research was carried out using 33 Arab stallions in three age groups including 2 to 6, 6 to 10 and 10-14 years old under the same nutrition and management condition in the July and January (2012) were as the representative of the heating and cold season, respectively. The experiment done in the Arab horse breeding fields of Dezful. The concentration of melatonin from serum samples was measured by HPLC (Bechgaard et al 1998; Itoh et al 1999; Peniston-Bird et al 1993 and Gupta et al 2006). The results of this research were analyzed using SPSS software (version 18). Comparison of serum melatonin concentration between the summer and winter seasons done by T-test. The difference of these parameters in two seasons, and in three age groups 2 to 6, 6 to 10 and 10 to 14 years old was analyzed with one-way ANOVA and multi-domain tests Duncan.
The results showed that mean serum concentration of melatonin hormone in winter (97.39 ± 16.4 pg/ml) non significantly was higher than summer (20.11±12.3 pg/ml). Research (Casao et al 2010; Altinsaat et al 2009; Elkon et al 2011; Wrench 2007; Cigdem et al 2009; Gerlach and Aurich 2000; Nagy et al 2000 and Guerin et al 1995) on changes in melatonin hormone and seasonal reproduction of Horse, were considered 8 hours of difference during the day between summer and winter seasons, as a factor for significant changes in the concentration of melatonin hormone and horse reproductive activity. Since, in the city of Dezful, the difference in the length of the day in summer (July) and winter (January) is approximately four hours, it can probably be argued that the difference in the length of the day (the duration of lighting) in The hot and cold season is not such as to make a statistically significant difference in the level of serum melatonin of Arab stallion between two seasons. The results indicate that the season has affected on the level of blood hormones, sexual behavior, physical and biochemical properties of semen and its fertility (Hafez and Hafez 2009). In addition, reproductive activity of the horse throughout the year continued with the fact that the size of the testicles, the number of Leydig cells, testosterone concentrations, and therefore the volume and concentration of sperm in the winter, decreased (Wrench 2007). In this study, in both seasons, the mean concentration of melatonin in the 2 to 6 year old stallion was significantly more than 6-10 years old and 10-14 years old (P Due to the shorter photoperiod in winter than summer, a rise in the level of melatonin in this season was seen, but photoperiodic changes between the two seasons are not so significant that the melatonin hormone exhibits significant changes. Therefore, it can be said that in the Arab stallion, the season has no effect on the concentration of serum melatonin, but it decreases with increasing age of melatonin concentration.