Restoration of reproductive capacity of stallions after suppression with exogenous testosterone.

Twelve stallions that had been given 0, 50 or 200 micrograms testosterone propionate (TP)/kg body weight every other day for 88 days were examined for the effects of androgen withdrawal on spermatozoal production, seminal quality and libido. Although the lower dosage did not affect most of the traits studied, the higher dosage severely reduced scrotal width, spermatozoal production, the number of sperm per ejaculate, the percentage of progressively motile spermatozoa and the percentage of normal spermatozoa. These adverse effects were found to be largely reversible. By 90 days after the cessation of treatment, scrotal width, testicular weight and spermatozoal production were similar for treated and control stallions. Although the number of sperm per ejaculate remained lower for stallions given 200 micrograms TP than for controls during the recovery period, the number of sperm in the extragonadal ducts was similar for all groups after 90 days of recovery. Spermatozoal motility and morphological characteristics were normal for all three groups by the end of the recovery period. Libido was not affected by TP treatment or withdrawal.