الفهرس 
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Abstract
The present study was designed to determine in vivo the effect of GnRH analogue (Buserelin acetate) on age at puberty, semen quality and fertility of immature and mature male New Zealand White (during summer). Another experiment was realized to analyze the putative effect of GnRH analogue on rabbit Leydig cell function. The first part of the experiments (in Egypt) shows that GnRH analogue has positive effects on body weight and also on the weights of testis, epididymis and accessory glands. Histological parameters were measured in both testis and epididymis of immature rabbits; they showed that the GnRH analogue treatment increased the relative volume and the diameter of seminiferous tubules, the average frequency of stages I and, VIII of spermato genesis, the number and diameter of both Sertoli cells and Leydig cells, the thickness of epididymal duct epithelium and the percentage of spermatozoa present in cauda epididymal duct, whereas a decreased of the relative volume of interstitial tissue was observed. The ages at beginning of fighting, at separation of penis from sheath, at mounting and at first ejaculation for GnRH -treated male rabbits were earlier than in control animals. All the parameters studied concerning seminal characteristics, fertilIty and plasma testosterone concentration were significantly higher for GnRH-treated animals compared with controls. During summer the injection of 2ug of Buserelin acetate 3 times weekly for two weeks, improved semen quality and fertility of New Zealand White rabbit bucks compared with control animals.