Abstract :
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 photoperiod. 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 C1 groups,
respectively P < 0.01; Exp 2: 1.04±0.07mL 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 C1 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.
