Age affected: Newborn.
Causes: Death and degeneration of foetuses after 35th day of pregnancy without abortion.
Effects: Significant if >1% of foetuses affected.
The pig foetus is implanted by day 35 and born at day 114 of gestation. It may die at any time between those days for a number of reasons. Piglets which die and remain in the uterus undergo a series of standard changes. The skin loses its colour, the eyes sink and the placenta becomes darker. As water is removed, the foetus becomes drier and finally becomes dark brown, enveloped in its placenta. If the dead foetus is infected, then it may swell and become oedematous and smell awful, but if infected with Trueperella pyogenes, it becomes a bag of creamy pus containing bones. The bones of the mummified foetus remain intact and so the crown-rump length of the foetus can be measured to establish the time of gestation at which death occurred. Mummified piglets are born with the remainder of the litter. Piglet death can result from infection with viruses such as porcine parvovirus, the enteroviruses of SMEDI, Aujeszky’s disease, and PRRS. Less common causes include Japanese B encephalitis in countries where it occurs.
Mode of transmission
Mummified foetuses may occur spontaneously as incidental findings when a foetus dies at the appropriate stage of gestation. Where the condition is common or occurs in successive litters, one of the diseases listed above may be responsible and be transmitted by the routes specific to that disease.
There are no clinical signs unless referable to a disease which causes foetal mummification or to the obstetrical problems which may result from the hard mummified foetuses being cleared from the reproductive tract at farrowing. The presence of mummified foetuses in the products of parturition may be overlooked as they may appear as hard, brown, rounded objects in the placenta.
The occurrence of mummified piglets in the products of parturition may be immediately apparent. To establish the number present or to confirm the absence of mummies, it is necessary to search through the afterbirth with care in order to identify the smaller foetuses which may be simple ovals or pellets of dark material. Having confirmed the presence of mummies, if more than 1% of the piglets born are mummified, reproductive tract disease may be present. The period of gestation at which death took place can be established by measuring the crown-rump length of the foetus and comparing it to standard growth curves. The identity of any causal agent can be established by its demonstration in the foetus by isolation, detection of antigens or detection of nucleic acids using the Polymerase Chain Reaction (PCR). In foetuses which have died after the development of immune competence (older that 70 days gestation) it may be possible to harvest fluid from the body cavities for the detection of antibody. Finally, the identity of the agent may be determined by serological testing of the sow.
Mummified piglets are usually passed with the other products of conception by the sow, but may be found incidentally at slaughter or in uteri being investigated following an outbreak of failure to farrow. The dead piglet varies in size with the stage of pregnancy at which it died, but generaly, the skin has lost its colour, the eyes are sunken and the placenta is dark. Foetuses are often dark brown but recognisable as a piglet and are wrapped in their placenta. If the dead foetus has been contaminated by bacteria, it may be swollen and oedematous and smell, in some cases appearing as a bag of creamy pus containing bones. The bones of the mummified foetus remain intact and so the crown-rump length of the foetus can be measured to establish the time of gestation at which death occurred. The dead foetus may be examined by the methods described above for the presence of infective agents or antibodies to them using the methods described above.
Treatment and prevention
There is no treatment for mummified foetuses as such because they have been dead for many days, however, any obstetrical problems such as blockages during parturition can be relieved and infection of the tract resulting from damage can be treated. When the cause of the mummification has been established and the time of its occurrence pinpointed, then preventive measure may be taken. In the case of parvovirus or Aujeszky’s disease for which vaccines are available, it is possible to vaccinate sows and protect subsequent litters from infection. The use of the mummified foetuses as ‘feed back’ in order to increase maternal immunity has been practised, but is unhygienic, requires the permission of the state veterinary authorities in some countries and may not work if the expected pathogen has disappeared from the mummies.