Effect of artificial long days and/or melatonin treatment on the sexual activity of Mediterranean bucks

The aim of this work was to determine whether treatments using photoperiod (long days) and/or exogenous melatonin are effective in enhancing reproductive activity during the natural anestrous season in Mediterranean bucks. Two experiments were carried out. In the first experiment, 19 adult bucks were allotted to 3 treatment groups. Fourteen bucks were exposed to 16 h of light/day (long day) for 98 days (late autumn-winter). At the end of the long day treatment, 7 bucks received 3 s.c. melatonin implants (LD-M group), and the other bucks remained a long day group (LD group, n =7). The control group (C1, n = 5), remained under natural photoperiocl. In the second experiment, 7 bucks received 3 s.c. melatonin implants (M group, n =7), while the other 5 bucks acted as the control group (C2, n = 5) during the spring equinox. During the natural sexual anestrous season (spring), the treated groups recorded higher plasma testosterone concentrations than the control groups. Reactivation of the natural reproductive season was delayed only in the LD-M group. All treated bucks recorded a higher mean semen volume, than the control groups (Exp 1: 1.16 +/- 0.04 mL, 1.16 +/- 0.04 mL, and 1.08 +/- 0.04 mL, for the LD-M, LD, and Cl groups. respectively P < 0.01; Exp 2:1.04 +/- 0.07 mL vs 0.77 +/- 0.05 mL, for M and C2 groups, respectively; P < 0.01). The percentage of bucks that ejaculated was modified by treatment in the first experiment (89 +/- 1.7%. 71 +/- 2.4%, and 88 +/- 1.9% for LD-M, LD, and Cl groups, respectively, P < 0.001). Results demonstrate that treating bucks with artificial long days and/or melatonin at Mediterranean latitudes can induce an increase in plasma testosterone concentration during the natural anestrous season. The long day treatment alone resulted in a less effective method of inducing adequate out-of-season buck sexual activity. (C) 2010 Elsevier B.V. All rights reserved.