Effect of male odour on LH secretion and the induction of ovulation in seasonally anoestrous goats

Abstract

Reintroduction of males to seasonally anoestrous goats triggers an increased LH pulse frequency which leads to ovulation and further cyclic activity (male effect). To clarify whether pheromones from buck hairs are involved, two experiments were carried out. (1) Five acyclic does were stimulated with buck hairs for 72 h. The LH, oestradiol, and progesterone concentrations were measured. (2) The immediate increase of LH secretion after olfactory stimulation was used as a bioassay to evaluate the biological activity of buck hairs, their diethylether extracts (DE-extract) and a polar (fatty acids) and nonpolar (fats & lipids) subfraction. For comparison 5α-androstenone and 4-ethyloctanoic acid (4-EOA) were included. (1) Stimulation with buck hairs led to heat and ovulation in two out of five does and heat symptoms without ovulation in another one. Four out of the five goats showed an increase in oestradiol concentrations. LH increased immediately after the onset of stimulation and showed a higher pulse frequency ( 2.60 ± 1.14/6 h, x ± s.d. ) compared to the pulse frequency before stimulation (1.60 ± 0.55/6 h). (2) None of the goats which were exposed to the smell of either 5α-androstenone or 4-EOA reacted with an increase in LH concentrations within 30 min, whereas all other treatments led to a reaction. Similarly, the mean LH concentrations were significantly elevated by 60% on the average after application of either buck hairs, DE-extracts, fats & lipids, or fatty acids. No significant change was measured after 4-EOA and 5α-androstenone. The data show that buck hairs contain pheromones which may stimulate the resumption of cyclic activity. The measurement of the sudden rise in LH concentrations can be used as a bioassay for further isolation steps.