EFFECTS OF LONG-TERM CONTINUOUS GNRH ADMINISTRATION ON THE PITUITARY-GONADAL AXIS IN EIDS DEER STAGS (CERVUS-ELDI-THAMIN)

Eld's deer stags (Cervus eldi thamin) (in groups of three) were contin uously administered gonadotropin-releasing hormone (GnRH) in control, low, medium, or high doses (0, 20.1 +/- 0.7, 83.3 +/- 2.6, and 292.9 /- 4.9 ng . kg(-1) . d(-1), respectively) via osmotic minipumps for si milar to 80 d to investigate the potential for precociously reactivati ng the pituitary-testicular axis during the nonbreeding season. Secret ory patterns of LH, FSH, and testosterone concentrations were qualitat ively similar among treatments. However, in the low-dose group, basal LH and FSH concentrations were both increased (p < 0.05) and pituitary responsiveness to a superimposed GnRH challenge was augmented (p < 0. 05) after 12 weeks of treatment compared with all other groups. Despit e these endocrine changes, continuous low-dose GnRH administration was not effective for precociously inducing testicular activity in this s easonally breeding species. High-dose GnRH administration initially in duced a transient increase in LH, FSH, and testosterone secretion and delayed but did not prevent, the seasonal decline in spermatogenesis. After 6-12 weeks of high-dose GnRH administration, however, attenuated pituitary responsiveness appeared to delay the normal seasonal reacti vation of the pituitary-gonadal axis. In conclusion, prolonged, contin uous low-dose GnRH administration did not effectively translate into a precocious onset of testicular activity; therefore, this specific app roach is unlikely to be useful for prolonging the fertile period in th is seasonally breeding species.