Natural and artificial methods for inducing the luteal phase in the koala (Phascolarctos cinereus)
Johnston, SD, McGowan, MR, O’Callaghan, P, Cox, R & Nicolson, V 2000, Journal of Reproduction and Fertility, vol. 120, no. 1, pp. 59-64.
A luteal or ovulation phase in the oestrous cycle of the female koala can be effectively induced by both the physical act of mating with a male or pharmacologically following a dose of the reproductive hormone human chorionic gonadotrophin (hCG).
Female koalas at Lone Pine Koala Sanctuary were divided into four groups. The females in each group were mated with a male but were interrupted at different points during the thrusting or ejaculation stages of copulation. For the first group, the male was allowed to mate the female for only half of the normal duration of the thrusting stage. Females in this group did not demonstrate an increase in blood progestogen concentrations, which indicated that a luteal phase had not been induced. Females in the second group were mated for the full duration of the thrusting period. The majority of these females were confirmed to have entered a luteal phase following this interaction based on high progestogen concentrations and the length of the following interoestrous interval, with pregnancy and birth resulting from the remaining interaction. The females in group three were mated for the thrusting stage and half of the typical duration of the ejaculation stage, following which all females fell pregnant and produced young. The final group of females copulated with males without interruption and all entered a luteal phase following mating with 60% producing young as a result. These results confirm the previous observation that the act of mating induces a luteal phase and perhaps ovulation in the koala, and furthermore that the success of this induction depends on the duration of the copulatory interaction. A separate group of females in oestrus were injected with 250 IU hCG, following which the females’ progestogen concentrations increased significantly. This finding indicates that this pharmacological method is similarly suitable for inducing a luteal phase in koalas.
The authors suggest that the phenomenon of luteal phase induction from the act of mating relates to a ‘copuloceptive reflex’ by which the thrusting of the male koala’s penis into the female’s urogenital sinus triggers ovulation. This reflex has been recorded in rabbits, in which the reflex can be similarly triggered by either physical genital stimulation or pharmacologically. This study may be the first to report this same capacity in a marsupial.
The observations made here suggest that interrupted mating could potentially be used as a technique to induce ovulation in female koalas before artificial insemination for captive breeding programs, except in the case that pregnancy occurs as a result of this interaction.
Summarised by Joanna Horsfall
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