PHA (Pulmonary hypoplasia with anasarca) or Hydrops foetalis is a genetic disease that affects Persian Sheep and their crosses. The disease affects the developing foetus and is uniformly fatal. The lungs of the growing foetus do not develop normally and the foetus retains a huge amount of fluid. As a result, at the end of gestation the lamb is massive, so large, in fact, that it is only on rare occasions that the ewe is able to give birth (to the dead lamb). The condition usually necessitates veterinary intervention at the time of birth, often in the form of a caesarian or alternatively euthanasia of the ewe.
The disease entered Australia inadvertently in the original Skilder imports of 2006. Coolibah Stud purchased a son of one of the original black speckle skilder imports from the importer. It became apparent that this son carried this genetic disorder when several of the foetuses that he sired were affected by the condition.
Fortunately Dr Imke Tammen, a researcher at the School of Veterinary Science, University of Sydney, whose special interest is the investigation of genetic-based disease in domestic animals, became involved in 2014. Blood samples from adult sheep and tissue samples from affected lambs were supplied by Coolibah Stud, the original importer and one other Persian breeder. This enabled Dr Tammen and her team to identify the genetic defect present on the Persian genome that caused the condition and also to develop a blood test to identify carriers. These were reported by Shernae Woolley in her PhD thesis for which she was co-supervised by Dr Tammen and Dr Brendon O’Rourke.
At Coolibah, all sheep descended from the original skilder ram that had been purchased and all others obtained from the original importer were subsequently tested for the disease. Six were found to be carriers. The heartbreaking decision was made to euthanise these animals so that the Coolibah flock could be certified free of the disease and anyone obtaining sheep could be guaranteed that the disease would not subsequently appear in their own animals.
For those interested in genetics, the gene mutation that causes this condition is on the ADAMTS3 gene and involves a single nucleotide deletion. Pulmonary hypoplasia medically describes under-developed lungs while anasarca indicates severe fluid retention leading to swelling. Affected ewes are unusually large during pregnancy. They look bloated and appear uncomfortable, being quieter than normal, reluctant to move and often preferring to lie down. On vaginal examination, it becomes apparent that the foetuses are profoundly large and swollen. Described as “bulldog lambs” in some areas, once delivered the massive swelling of the stillborn lamb is readily apparent.
Although PHA is still present in Australia and is something that breeders of Persians, cross-bred Persians and other sheep that contain Persian blood need to be mindful of, the situation could be much worse. Thanks to Imke and the work of the other skilled scientists at Sydney University and the co-operation of several Persian breeders soon after the introduction of the breed into Australia, the impact of the disease has been dramatically reduced. At the same time, our awareness and understanding of this disease have been developed together with a test to detect carriers. Thus, control of the disease is now available.