Seasonal variations in serum concentrations of melatonin, testosterone, and progesterone in Arabian horse

Abstract

Summary:The objective of this study was to characterize seasonal variations in serum concentrations of melatonin, testosterone, and progesterone in Arabian horses under natural photoperiodic conditions. Peripheral blood samples were collected during breeding and non-breeding seasons from mares and stallions. Serum concentrations of melatonin, testosterone, and progesterone were determined by radioimmunoassay. Serum concentrations of melatonin were greater in the non-breeding season (42.41±1.59 and 37.68±1.55 pg/ml) when compared to breeding season (23.52±1.24 and 17.22±2.10 pg/ml) in both mares and stallions, respectively. Melatonin concentrations were low but not different between the luteal and follicular phases during breeding season in cyclic mares. Mares had greater concentrations of melatonin than stallions in both breeding and non-breeding season. Mean concentrations of testosterone were greater during breeding season (6.58±0.50 ng/ml) than non-breeding season (3.64±0.48 ng/ml) in stallions. There was a negative correlation (r=-0.658, p<0.01) with melatonin and testosterone levels in both season in stallions. A negative correlation (r=-0.829, p<0.05) in luteal phase and a positive correlation (r=0.847, p<0.05) in non-breeding season were found between melatonin and progesterone concentrations in mares. We conclude that changes in day length act as a regulator and photoperiod can be used to modify the seasonal reproduction in Arabian horse.Key words: Arabian horse, melatonin, photoperiod, progesterone, testosterone. Arap atlarında serum melatonin, testosteron ve progesteron seviyelerinin mevsimsel değişimleriÖzet: Bu çalışmanın amacı, doğal fotoperiyodik koşullarda Arap atlarının serum melatonin, testosteron ve progesteron seviyelerinin mevsimsel değişimlerini belirlemektir. Kısrak ve aygırlardan üreme döneminde ve üremenin olmadığı dönemde toplanan kan örneklerinden, radioimmunoassay yöntemi ile serum melatonin, testosteron ve progesteron seviyeleri belirlenmiştir. Sırasıyla hem kısrak hem de aygırlarda melatonin seviyeleri üremenin olmadığı dönemde (42.41±1.59 ve 37.68±1.55 pg/ml) üreme dönemine göre (23.52±1.24 ve 17.22±2.10 pg/ml) daha yüksek bulunmuştur. Üreme döneminde östrus siklusu gösteren kısraklarda melatonin seviyelerinin düşük fakat luteal ve foliküler dönemler arasında fark yoktu. Kısraklar hem üreme döneminde hem de üremenin olmadığı dönemde aygırlara göre daha yüksek melatonin seviyelerine sahipti. Aygırlarda üreme dönemindeki (6.58±0.50 ng/ml) testosteron seviyeleri üremenin olmadığı dönemden (3.64±0.48 ng/ml) daha yüksekti. Aygırlarda her iki dönemde melatonin ile testosteron seviyeleri arasında negatif bir ilişki vardı (r=-0.658, p<0.01). Kısrakların melatonin ve progesteron seviyeleri arasında ise luteal dönemde negatif (r=-0.829, p<0.05), üremenin olmadığı dönemde de pozitif bir ilişki (r=0.847, p<0.05) bulundu Bu çalışma ile Arap atlarında, gün uzunluğundaki değişikliklerin mevsimsel üremede bir düzenleyici olarak görev aldığı ve fotoperiyodun bu düzenlemede değiştirici etkisi olduğu ...

Seasonal variations in quantitative and qualitative sperm characteristics in fertile and subfertile stallions

“…The seasonal changes affecting reproductive capacity are translated into remarkable increases in the size and the function of the reproductive organs in both male and female animals (Gerlach and Au-rich, 2000). The environmental signals such as temperature and photoperiod interact with the endogenous mechanisms in which the reproductive activity of the seasonal breeders is affected (Aurich, 2011). Likewise, horses show increased reproductive activity during spring and summer when the temperature and the onset and length of daylight are very appropriate and the food is available, whereas these factors de-creased reproductive activity in the winter months (Gerlach and Aurich, 2000;Pickett et al, 1976).…”

“…In stallions, seasonal variations were found to involve testosterone and luteinizing hormone (LH) concentrations, sexual behaviour, semen volume, sperm output, and sperm motility, which were found to be higher in spring and summer compared to winter. Mares also exhibit increased reproductive capacity in spring and summer, which is reflected in sexual behaviour, hormonal levels in the blood such as LH, follicle-stimulating hormone (FSH), and gonadotropinreleasing hormone (GnRH), and the size of follicles and ovary (Aurich, 2011;Altinsaat et al, 2009;Janett et al, 2003;Gerlach and Aurich, 2000;Clay and Clay 1992).…”