Dr Colin Walker

Since 2006, no sheep genetic material had been imported into Australia – no semen, no embryos let alone any actual sheep. This all changed in the later part of 2021 when some Valais Blacknose frozen embryos and semen arrived. The import process had been lengthy and expensive. It had also attracted some controversy. Many were pleased that it had simply been possible to import some sheep genetics while others argued that, even though the risk of exotic disease introduction with the shipment was very small, it was still a risk not worth taking, in particular, for a breed that had dubious true commercial value, appealing mainly to the pet market.

The Australian Government's Biosecurity Import Conditions ( BICON) database houses the requirements to import more than 20,000 different types of plants, animals, minerals and biological products. BICON helps potential importers determine what import conditions exist. After reading BICON I had some questions and contacted the Victorian Department of Agriculture, Water and the Environment. The staff were most helpful and with their assistance I have summarised the requirements that need to be met to import sheep genetics. Although it is not currently possible to import live sheep, it is possible to import sheep genetics in the form of semen and embryos. The sheep that donate these must be free of a prescribed list of diseases. These diseases and the requirements that need to be met to ensure that the sheep are free of them are listed below : -

1. Foot and Mouth Disease – Foot and mouth disease (FMD) is a severe, highly contagious viral disease of livestock, including sheep. There is no specific test that the department considers to be suitable to reduce the biosecurity risk to lie within Australia’s appropriate level of protection (ALOP). The only assurance that is acceptable is that the exporting country must be completely free of the disease.
    
2. Sheep Pox --- The exporting country must be free of Sheep Pox. This requirement may cause some confusion with Australian breeders. In Australia, we have a disease caused by a pox virus called Scabby Mouth. However this disease is caused by a virus of the Parapoxvirus genus .The causative agents of Sheep Pox (and Goat Pox), as defined by the World Organisation for Animal Health (an intergovernmental organization coordinating, supporting and promoting animal disease control), are Sheep Pox virus and Goat Pox virus, respectively, both caused by strains of a different virus which belongs to the genus Capripoxvirus. These diseases are exotic to Australia.
    
3. Scrapie -- Scrapie is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs) similar to Mad Cow Disease. It is thought to be caused by a prion. Prions are virus- like  organisms made up of a protein that affects the brain. This is a difficult disease to assess. The disease can take many years to appear and an important way of assessing the animal is to have the sheep’s brain examined microscopically. This therefore involves euthanasia of both the rams and ewes that have contributed semen and eggs. Donors must be over 5 years old, have lived only in the export country, the exporting country must have Scrapie control measures in place as described in BICON and the donors must come from flocks meeting the requirements set out in BICON. Also, as different sheep have different genetic susceptibility to this disease, only stock with a genetic makeup ( ie an approved PrP genotype ) that is susceptible to Scrapie are permitted. Assessments of an approved genotype are complex and involve analysis of information on the PrP genotype of the breed as received from the competent authority of the exporting country, along with current available scientific research regarding scrapie genotypes and susceptibility.
   Meeting the Scrapie requirements is one of the most challenging parts of the importation process for breeders. Sheep over 5 years of age must be obtained. These are often the better animals that the farmer has retained. After all “live sheep” tests are done, the ewes are usually super- ovulated, inseminated and then the embryos flushed and frozen. Both ewes and rams are then killed and their tissues including their brains examined. Only when negative results are returned can importation proceed.
    
4. Bluetongue --- This is a viral disease transmitted by blood- sucking insects such as mosquitoes. Standard blood tests (ELISA and PCR) are done to check for infection. Vaccination can affect these results and so, if the sheep have been vaccinated, they must meet the requirements as set out in BICON
    
5. Brucella melitensis - This is a bacterium that causes abortion in sheep and can spread to humans, causing severe disease and death. The bacteria are transmitted from sheep (and other animals) to humans by ingestion of infected food products, direct contact with an infected animal, or inhalation of aerosols. The department accepts either country freedom or testing of donor animals belonging to a flock that is officially free from B. melitensis . The tests are blood tests, which can be done on the live animal or collected at autopsy.
    
6. Contagious agalactia – Contagious agalactia is a Mycoplasmal disease of sheep and goats that can cause serious economic losses from mastitis, arthritis and eye infections. Septicaemia (blood poisoning) and pneumonia also occur during some outbreaks, most often in young nursing animals. Mycoplasma are a type of intracellular bacteria. Sheep must come from a property where this disease has not been diagnosed in the previous 6 months.
    
7. Maedi-visna –  This is a slow virus disease of sheep that is invariably fatal. It is highly contagious and mainly transmitted through the ingestion of milk from a virus- infected sheep although disease can be spread within flocks through direct contact. Donors must come from a flock meeting the requirements set out in BICON and test negative.
   
   It is worth noting  that all donors, rams and ewes, must satisfy the same screening requirements. Clause 16 in BICON requires that ‘The semen donors were of equivalent tested health assurance standards to those prescribed for the female donors’.This means that the tests and requirements listed above not only apply to donor ewes but also to the rams. Consequently for Scrapie health status evaluation, the semen donor (ie the ram) needs to be euthanised, autopsied and tissues tested for the Scrapie prion protein in the same way as the embryo donor (ie the ewe).
   
   There are also requirements that embryos must meet. Embryos must be produced using fresh semen used in an approved way as set out in BICON. Collected embryos must be handled using specific guidelines as set out in BICON ,which aim to avoid cross- contamination. The embryos must be fertilized in vivo (ie in the ewe) and the zona pellucida (the thick membrane that surrounds the egg before it implants) must be intact. The embryos can only be handled by approved personnel and stored, handled and shipped in an approved way, as set out in BICON.
   
   Also sheep embryos can only be considered for importation from permitted countries, primarily UK, USA, EU, Canada and NZ. Notably ,they cannot be imported from Africa, the Middle East or Asia. This, unfortunately, precludes any further importation of African breeds unless flocks are established in the listed approved countries. The import conditions do vary between the approved countries. In particular, the import conditions from New Zealand do not specifically require freedom from FMD or Sheep Pox , nor do they require testing for any of the diseases listed. Essentially, the exporting country’s health status and individual trade and market access negotiations with the Australian Government play a role in the specific import conditions applied for sheep embryos collected in and exported from that country.
   
   These import restrictions and our island location have enabled Australia to remain free of many of the most severe and economically significant diseases found around the world. For ruminants such as sheep, most of the vesicular diseases such as FMD and slow virus and prion diseases such as Scrapie and Maedi Visna do not occur in Australia. Our disease- free status is the envy of many countries and places us in a unique situation to, in turn, supply our own genetics to the rest of the world. For example, I find it ironic that in the last 8 years we at Coolibah Persian Sheep Stud have exported about 80 Persians in four shipments to the Middle East. Why would breeders source Persians from Australia when the breed’s natural home is relatively close in sub-Saharan Africa? Part of the answer is that Australian sheep are, quite simply, healthy. Everyone wants to keep them that way and so with responsible breeders and vigilant government departments working together, this situation should persist.