Behavioural cycles during Pseudopregnancy in confined populations of domestic rabbits and their relation to the histology of the female reproductive tract
Female domestic rabbits living with vasectomized males in large compounds (3/16 ac in area) exhibited periods of sexual attraction and mating, together with other behaviour such as aggression towards other females, digging, burrow interest, and nest building at intervals of about 6 days or multiples thereof. The behavioural cycles occurred during pseudopregnancy (of about 18 days) and were not a manifestation of an underlying inherent sequential cycle or a typical mammalian oestrous cycle. Behaviour with a strong sexual component culminating in mating and ovulation was observed at the beginning (or end) of each of 54 pseudopregnancies. Similar behaviour was also grouped about either the sixth or twelfth days of pseudopregnancy or both. This behaviour was extremely variable in both incidence and the number of components involved. Sexual components occurred less frequently and only once culminated in mating and ovulation. The behaviour observed on the sixth and twelfth days of pseudopregnancy was not reflected in measures of physiological activity such as numbers of graafian follicles, diameter of graafian follicles or corpora lutea, or weight changes in ovaries or uteri. The histology of the ovaries, uterus, and vagina and dimensional changes such as ovarian and uterine weights, number and diameter of graafian follicles, and diameter of sets of corpora lutea showed no detectable difference from those reported by other workers during pseudopregnancy for caged female rabbits isolated from males. The incidence of 6-day and 12-day behaviour was highest in the autumn-winter months when sub-optimal reproductiveconditions prevailed and lowest in spring-summer. Some possible causal mechanisms and the adaptive significance of the sixth-day and twelfth-day periods of sexual behaviour are discussed.