Effect of pulsatile or continuous administration of GnRH on reproductive function of stallions

Abstract

Gonadotrophin-releasing hormone (GnRH) was administered subcutaneously to reproductively normal stallions, either in a pulsatile manner (10 micrograms GnRH/2 h; n = 6) or as a continuous infusion (10 micrograms GnRH/2 h; n = 6), and in a pulsatile manner to 9 reproductively abnormal stallions, from February to July, 1988. Hormonal secretion patterns, testicular parameters and semen characteristics were monitored before and during treatment. In general, pulsatile GnRH caused a significant increase (P less than 0.05) in luteinizing hormone (LH) concentrations in the peripheral blood of normal stallions. LH levels also appeared to increase in abnormal stallions but the rise was not significant (P greater than 0.05). Stallions given GnRH by continuous infusion and the untreated control stallions did not show an increase in LH concentrations during the treatment period. None of the treatments resulted in significant increases in peripheral blood concentrations of testosterone, although individual stallions that showed an increase in LH secretion appeared to show some increase in testosterone secretion rate. In general, and for individual stallions, none of the treatments resulted in increased total scrotal width, total number of spermatozoa per ejaculate or the percentage of progressively motile spermatozoa in the ejaculate. It was concluded that although pulsatile administration of GnRH may increase the secretion rate of LH and, consequently, testosterone, this adjustment does not increase testicular size or output and motility of spermatozoa.