This note describes feral pigs (Sus scrofa) which are the descendants of domestic pigs that escaped and have bred in the wild. There were pigs aboard the First Fleet in 1788, and in later arrivals to the developing colony.
The animal husbandry techniques of the first settlers left quite a lot to be desired. Pigs were often allowed to roam at will during the day, and were collected at night - if they could be found.
Given such herding practices, it is not surprising that, before long, colonies of feral pigs were well established in New South Wales.
At around the same time in the 1820’s, pigs were imported into the north of Australia; these herds also thrived and developed widespread feral populations.
Feral pigs spread widely and rapidly throughout the northern and eastern regions of the country, creating considerable amounts of damage wherever they became established.
A 1981 estimate of the cost to Australian primary industry of feral pig activity put it at over $50 million per annum. Victoria did not have problems with feral pigs until fairly recently. In 1959, some pigs were reported in the north of the State.
It is unclear exactly how these animals came to establish themselves in Victoria.
There is some evidence to support the contention that they were caught in NSW., brought illegally across the border and deliberately released by amateur shooters. Once established in the floodplains bordering the Murray River, the pigs were able to breed unhindered. By 1962, they had prospered to the point where they were a problem in several country shires.
In 1975 the number of shires reporting the presence of feral pigs had risen to fifteen. By 1978, the figure was twenty-three. Feral pigs are now in all Department of Natural Resources and Environment Regions of the State.
The majority of feral pigs in Victoria are to be found at various spots along the Murray River, and also near Mansfield, Kinglake, the Grampians and Lancefield. The other areas of the State where feral pigs are known to exist are not large and it is unlikely that there will be a further spread from these areas due to the amount of human activity around them.
Behaviour and breeding:
Feral pigs can breed throughout the year in Australia. A sow begins breeding from about six - eight months of age, when her weight exceeds 30 kg. Litter sizes vary, but the average is 6.5 per litter at birth. Depending on seasonal conditions, up to five piglets may eventually be weaned.
Two litters can be weaned in 12 -14 months, thus feral pigs can multiply at a very fast rate. A New South Wales study suggests that in a relatively good season, a potential rate of increase of 300% per annum is possible.
Pigs are omnivores. They have definite preferences in their diet with succulent green vegetation forming the major food item if it is available. If this is scarce, they will become increasingly dependent on animal material and plant roots. Grain is also a highly attractive item, even when other fodder is readily available.
Feral pigs are, for the main part, nocturnal animals. Like domestic pigs they have a low tolerance to heat and, if temperatures rise consistently above 30o C, they will need water daily. A pig held in a yard without shade or water can die in six hours.
It is not surprising then that the largest concentrations of feral pigs in New South Wales are found on flood plains, marshes and river frontages. Pigs are very efficient swimmers. Wild pigs can reach a formidable size, a sow may weigh as much as 100 kg, while some boars exceed 150 kg.
Disease:
Feral pigs are carriers of a number of serious diseases such as leptospirosis, brucellosis, sparaganosis, tuberculosis and others that are dangerous to humans as well as livestock.
The major problem that feral pigs present is the role they could play in the spread of ruinous exotic diseases which have the potential to seriously damage primary industry in Australia, should they ever become established. Feral pigs are susceptible to diseases that include African swine fever, Aujeszky’s disease, foot and mouth, rabies and rinderpest.
None of these diseases are at present in Australia, however, it is a matter of concern that the widespread distribution of feral pigs, particularly in Northern Australia, would make effective control extremely difficult. Some outbreaks have occurred in the past but fortunately, these have been localized and controllable.
In 1923, rinderpest was discovered at Fremantle in Western Australia. Swine fever outbreaks have been recorded in 1927 and 1928 in Victoria and New South Wales, and again in 1961 in New South Wales. Teschen disease is suspected to have occurred in New South Wales in 1966.
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