Efeito da melatonina exógena sobre os aspectos reprodutivos em carneiros deslanados no agreste meridional do estado de Pernambuco

Abstract

Ovine are characterized as seasonal poliestrous animals, where reproductive activity is intensified in certain times of the year, with interdependence of a greater or lesser exposure to sunlight or photoperiod. Although sperm production of rams stay stead the whole year, it is well known that there is a drop of seminal quality during the period of non-reproductive breeding season mainly in temperate regions where such photoperiod effect is punctual. However, few studies have been devoted to the influence of photoperiod on reproduction of sheep in tropical regions where variability of photoperiod is shorter. The objective of this experiment was to test the effectiveness of exogenous melatonin on seminal quality improvement in hair sheep at Agreste Meridional Region of Pernambuco State. Eight Santa Inês hair sheep were divided into 2 groups of 4 animals, a treatment group (TG), subjected to exogenous melatonin subcutaneous implants (Melovine ®, CEVA), and a control group (CG) subjected to subcutaneous application of 1 mL of saline as a placebo. Both groups were kept in barns with a mean luminosityof 11.26 hrs/day, for 120 days. During this period, it was evaluated the effect of exogenous melatonin on scrotal circumference, sperm concentration and serum concentrations of testosterone and melatonin by nightly and morning blood sample collections to establish influence in the concentrations of these hormones, correlating with the effect of seasonality. Data were compared using analysis of variance (ANOVA). The contrasts between means were evaluated through Student-Newman-Keuls test. There was a significant increase in serum concentration of melatonin in TG compared to CG, on the first 3 morning and evening collections (p < 0.05). No differences were observed in the 2 latest. Serum concentration of melatonin has demonstrated a night/day rhythm characteristic in both TG and CG groups with a difference in the mean concentration ofCG melatonin in the morning (3.9 pg/mL) compared with the night sample (59.56 pg/mL), however, this difference was not observed in TG (572.45 pg/mL vs 939.52 pg/mL). An increased serum concentration of melatonin was directly proportional to the increase in scrotal circumference. Also, a significant increase was observed in sperm concentration in TG 45 days after the placement of implants. Serum testosterone concentration increased significantly in TG 45 days after placement of the implants when it began a decline in concentration of melatonin. The results of this study demonstrated that treatment with exogenous melatonin in hair sheep at tropical region had a positive effect on scrotal circumference, on sperm concentration and on serum testosterone concentration suggesting that even in tropical regions where there is not a marked difference in photoperiod, melatonin plays a role in the reproductive processes.