Studying the effect of age and season on the concentration of testosterone hormone and the size of scrotum circumference in Arabian stallion

In order to study the effects of age and season on concentration of the blood serum testosterone and the scrotum circumference, blood samples were taken, in summer (July) and winter (January) from jugular vein of 21 purebred Arabian stallions categorized in 2-6, 6-10 and 10-14 years of age. The concentration of the blood testosterone and the size of scrotum circumference were measured by the standard radioimmunoassay and collis vernier, respectively. Comparison of subjected parameters between summer and winter seasons were conducted using t-test and the differences among the three age groups in two seasons were done by one-way ANOVA, fitting Duncan test as implemented in the SPSS software. Results showed that there were not significant differences in blood serum testosterone concentrations between summer and winter seasons (P>0.05). The average size of the scrotum circumference in the summer season was significantly greater than that observed in winter (P<0.05). In the winter, the average testosterone concentration in the stallions of 10 to 14 years of age was significantly greater than 6 to 10 years-old stallions (P<0.05), but in the summer, the average concentration of testosterone did not varied significantly between age groups (P>0.05). Also, the size of scrotum circumference in three studied age groups was not significantly varied between two seasons (P>0.05). The results showed the increasing levels of testicular volume and testosterone in the summer that is evidence of increased reproductive activity, But don’t observed the increase or decrease in the mean testosterone level and scrotum circumference in 3 age 2 to 6, 6 to 10 and 10 to 14 years in both seasons.