Annual and seasonal variations of testicular and pituitary-thyroid axis activities in bucks native to sahara desert

Abstract

This study was conducted to assess comparative annual and seasonal patterns described in morphometric parameters, sexual and thyroid activities in indigenous bucks native to Sahara Desert. Seven adult bucks were used to establish seasonal patterns of body weight, testicular volume, plasma testosterone concentration measured by radioimmunoassay and pituitary-thyroid axis activity estimated by plasma concentrations of TSH, FT3 and FT4 measured by enzyme-linked fluorescent assay. The results showed monthly and seasonal variations characterized by a minimum in January for body weight, from December to February for testicular volume, followed by plasma testosterone concentration in March; they progressively increased to their respective maxima reached in July, August and September when ambient temperature and photoperiod were the highest. In October, there was a rapid fall in testosterone levels, preceding that of body weight and testicular volume (P<0.001). Plasma TSH showed no significant variations, while the monthly rhythms of FT4 and particularly FT3 (P<0.001) were inverted to the sexual cycle, since the highest values occurred in winter (January) and the lowest in summer (July). These results suggest morphometric and hormonal interrelations in this indigenous seasonal breeder goat in order to survive and reproduce in its natural arid environment.

Keywords

• buck
• sahara desert
• seasonal variations
• testicular activity
• thyroid activity