. Objective: To evaluate seasonal variation in sexual behavior of Pars Grey rams.
Animals: Six healthy Fars Grey rams (3-4 years old).
Procedure: All rams were exposed fortnightly to ewes and the following indices were evaluated: 1) number of mounting 2)
number of mating without ejaculate 3) number of ejaculation
4) reaction time. The test was carried out by exposing two rams to two ewes in a 20 minute period. Ram efficiency was
calculated by dividing the number of ejaculation by the sum
of number of mating with and without ejaculation. Blood samples were also collected immediately after each sexual
behavior test to determine plasma testosterone concentrations.
A commercial ELISA hormone assay kit was used to measure plasma testosterone concentrations. Statistical analysis: Chi-square test and GLM procedure in
ANOVA of SAS.
Results: Testosterone concentrations varied between 3.6 ng/ml in autumn to 10.3 ng/ml in summer (P<0.05). A
significant (P<0.05) seasonal effects was observed in the
number of ejaculation in summer (0.9) and in winter (2.2).
Rams showed a significant individual variation in the number
of ejaculations (P<0.05). The highest number of mating
without ejaculation was recorded in winter (7) whereas rams showed the lowest corresponding value in autumn (2.5). Ram efficiency was varied among rams (P
significant seasonal variation was observed in the ram
efficiency (P<0.05). Conclusions: There was a significant increase in the mean
plasma testosterone concentrations in summer, particularly in
late summer. The ram efficiency reached to the highest level
in autumn, shortly after a decrease in plasma testosterone
concentrations. Therefore, it can be concluded that the rise in
ram efficiency is a delayed effect of the increase in mean plasma testosterone concentration. The results of this study also emphasize the need of evaluation of breeding rams for
their sexual behavior prior to mating season. This is due to the individual variation that is observed among Fars Grey rams.
An scoring system in the sexual behavior of breeding rams
needs to be developed to make the test a useful tool in ram
selection. J.Fac.Vet.Med.Univ.Tehran. 60,1:49-52,2005.
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