Do cyclic female goats respond to males with an increase in LH secretion during the breeding season?

Abstract

The male effect is currently only used during seasonal or lactational anoestrus because the response is thought to be blocked in cyclic females by periods of elevated progesterone. In this study, we tested whether cyclic, female goats would respond to male exposure with an increase in pulsatile LH secretion. During May (breeding season; Southern Hemisphere) the cycles of 16 Australian Cashmere goats were synchronised using intravaginal progesterone pessaries. Pessary insertion was staggered to produce groups in their early luteal (EL; n = 8) and late luteal phases (LL; n = 8). The LL group was retrospectively subdivided into mid-luteal (ML; n = 4) and late luteal (LL; n = 4) groups due to differences in oestrous cycle length that emerged during the study. Male exposure stimulated an increase in LH pulse frequency in the EL and LL groups ( P < 0.01) but not in the ML group ( P > 0.1). This increase was accompanied by an increase in basal and mean concentrations of LH in the LL group ( P < 0.05) but not in EL ( P < 0.1) or ML ( P > 0.1) group. There was no effect of male exposure on LH pulse amplitude ( P > 0.1). Progesterone concentrations differed among all groups on the day of male exposure ( P < 0.05) and declined significantly over the 12-h sampling period in the LL group ( P < 0.05). Prolactin concentrations declined in the EL group but did not change significantly in the ML or LL group. In conclusion, male exposure induced an increase in pulsatile LH in goats in the early and late luteal phases of the oestrous cycle. The high concentrations of progesterone in females in the mid-luteal phase appeared to block the male effect.