Active anti-paternal immunization does not affect the success of marsupial pregnancy

Active anti-paternal immunization does not compromise pregnancy in eutherian mammals. However, in an earlier study in a marsupial, grafting with paternal skin appeared to have resulted in transient infertility. In the present study, by critically monitoring the breeding efficiency of tammar wallabies sensitized against their mate's transplantation antigens, we aimed to resolve the question of immunologically mediated infertility in marsupials. Eight experimental females received two full-thickness skin grafts from their prospective mate and eight controls grafts of their own skin. The experimental group were monitored for 30 reproductive cycles and produced 24 pouch young (PY), whereas the control animals produced 28 young from 33 cycles. Five of the 11 apparently non-fertile cycles were judged to be normal pregnancies where the young had failed to reach the pouch (cycle length less than 28 days; rapid plasma progesterone decline coincident with oestrus). True infertility was thus limited and, although occurring mainly in the male-skin grafted group (5 cycles), this was not significantly different (chi 2, P greater than 0.5) from the controls (1 cycle) and represented the effect of one very poor breeder. We conclude that allogeneic pregnancy in marsupials is not compromised by active anti-paternal immunization. Infertility observed here, and in the earlier study, reflected disturbance of breeding owing to handling of the animals or the poor reproductive efficiency of individual animals in small experimental groups.