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Footrot in the Central West
P.J. Ahrens, B.V.Sc., M.A.C.V.Sc., Veterinary Inspector, MOLONG
DESCRIPTION OF THE AREA
The territory of R.V.0. Central West consists of five Pastures Protection Districts - Bathurst, Carcoar, Forbes, Condobolin and Molong - encompassing an area of about 5 million hectares. The two eastern Pastures Protection Districts cover part of the pastoral zone known as the central tablelands with altitudes of 700-1200 metres. The topography falls away irregularly to the west until it becomes very flat at the Condobolin end, where the altitude is about 300 metres.
Over the last 30 years a great deal of land has been cleared, superphosphate applied and improved pasture established. Sub-clover pastures which favour the spread of footrot became widespread on the tablelands and slopes in this time.
Footrot is endemic both inside and outside this area.
STOCK POPULATION
The sheep population in the area is estimated at about 9 million. Sheep flocks range in size from a handful up to 30,000 head, but there are very few over 5000 in number. There are about 10,000 sheep properties. About half the sheep population is merino and the remainder mostly border leicester crossed with merino and the 3rd cross lambs, typically with dorset or suffolk as terminal sires. Crossbred sheep predominate in the more fertile pockets such as around Bathurst, Oberon and Orange, while merino sheep predominate in the less improved more extensive country between these pockets, and in the west. There are a variety of commercial goals in the sheep industry - woolgrowing, fat lamb raising, first-cross ewe rearing and stud breeding. However, commercial goals can alter rapidly with seasonal prospects and sheep owners traditionally like to maintain a degree of flexibility in their options.
The cattle population in the area stands at about 700,000 which means that the cattle industry rivals the sheep industry in importance. There is also a substantial goat population which has built up in only recent years.
SHEEP MOVEMENTS
Marketing of sheep from this region can be in the form of paddock sales or through saleyards. The regular sales at major saleyards handle mainly sheep for slaughter but there are always a few store pens for small time dealers and unwary hobby farmers. Special store sales are held from time to time when occasion demands, and these are conducted either at the major saleyards at Bathurst, Orange, Blayney, Forbes and West Wyalong or at minor saleyards such as Wellington, Peak Hill, Gooloogong, Canowindra and Grenfell. Occasional breeder sales are also held, either on properties or at saleyards.
Marketing of sheep to saleyards outside this district is mainly to Dubbo, Cowra, Goulburn and Homebush. Paddock sales either for slaughter or as a property to property arrangement is a major marketing avenue.
Acquisition of sheep for fattening, breeding or woolgrowing purposes is naturally an important part of the sheep industry, but the necessity to keep clear of foot disease is well understood by the managers of established flocks. Many owners try to maintain closed flocks except for ram purchases. When they are in a position of having to buy ewes or wethers they tend to go west for their supplies. There is less likelihood of footrot in western origin sheep but the possibility still exists.
Rams are purchased from local or distant breeders and are occasional sources of B. nodosus infection. Even rams at inspected Breed Society sales have been known to have virulent footrot.
Traffic in sheep is generally much less these days than it used to be. Sheep dealing is now confined to only a small sector of the industry, due in no small measure to the fear of footrot.
CLIMATE AT FOOT LEVEL
Rainfall in the area varies from 1500mm per year in the eastern mountains to 500mm average on the lower slopes, but the rainfall is extremely variable from year to year and there is no particular seasonal pattern. Rain can fall at any time, or may fail to eventuate for months (or years) at a time. Footrot 'transmission periods' therefore vary enormously from year to year. On average there is a total of 1-2 months when footrot will transmit, but this varies from 6-8 months in some years to nil in others.
Temperatures in the region can be sustained below 10°C for long periods in winter time, especially at the higher altitudes, but there is always the possibility of a period of milder weather during which footrot transmission can occur.
Where improved pastures have been established, the climate at foot level is more frequently conducive to footrot transmission than in native pastures. For this reason, as well as rainfall distribution, the prevalence of footrot is much greater in the pasture improved areas of the tablelands and slopes than in the western districts. However, the irrigation flats along the Lachlan River provide the same microclimate for sheep feet and thus a zone of higher prevalence of the disease. Generally, footrot in the arid western sector is virtually unknown.
PREVALENCE OF FOOTROT
Footrot is not a notifiable disease and there are no accurate figures on property prevalence let alone the prevalence in the sheep population. It is estimated that 100-200 properties could be affected with virulent footrot, and possibly twice that number harbour the benign forms of the disease. A much greater percentage of sheep properties have experienced footrot at some stage in living memory but the disease has been eliminated.
The prevalence of footrot is higher in merino sheep than in British breeds or their crosses, due no doubt to the difference in anatomy of their feet. During the recent series of droughts, footrot appeared to diminish to very low levels, but with the advent of two good seasons the disease has resurfaced and new properties have become infected. Just how much of the high prevalence in wet years is due to spread from property to property and how much is due to activation of latent carriers in each flock is unknown.
BOUNDARY FENCES
Few landholders in the region are confident in the security of their boundary fences at all times. Creek crossings are always a weak point, and damage by wild pigs and kangaroos in less closely settled areas is not uncommon. Also an otherwise adequate fence may be only a minor obstacle to a large border leicester sheep, or goats domestic or feral. Cattle breaking through a boundary fence have also been known to transfer infection from a neighbour's property. Vehicles driving through have also been suspected to introduce infection on tyres or footwear.
As the N.S.W. regulations now stand, there is no requirement for the owner of a property adjoining an infected property to be informed about the risks he faces. If a neighbour is uncooperative, there is little protection provided under law. The Dividing Fences Act cannot be used except where public quarantine has been imposed.
Nevertheless, 'footrot-conscious' sheep owners (those who have had to eradicate footrot) are usually able to maintain an effective boundary, though in certain areas they may have to be vigilant for damage caused by kangaroos or wild pigs and the entry of goats.
FOOTROT ERADICATION
There is an element of social stigma about footrot which makes the disease difficult to discuss with groups of people or even individuals. It also makes owners irrational in their dealings with affected sheep - to the extent that owners have been known to cut the throats of hoppy sheep (in a rage) as a sort of desperate control measure. Sheep owners (or managers) can be classified into 3 types:
Type 1
Those whose flocks have been recently affected. An outbreak of virulent footrot in such susceptible sheep is usually severe and dramatic and the owner is anxious to get rid of it as soon as possible. The main task of the veterinary advisor is to work out the least costly method and to guide the owner's eagerness into fruitful channels.
Type 2
Owners who can see the advantages of eradication and who can be encouraged to look at the options. With effective communication these people will embark on an eradication programme, either by selling off groups of sheep or by inspection paring techniques as described in Department of Agriculture pamphlets, or more recently the 'Footrite' brochure. There is a considerable financial advantage in carrying out eradication covertly (without official supervision) because lines of reasonably well cleaned up sheep can be sold at saleyards instead of having to go direct to abattoirs as morality would dictate. The task of actually going through eradication with these sheep is not worthwhile, but the risk of an Inspector finding footrot in the sheep at the saleyards is remote.
Nevertheless some Type 2 owners have failed in their attempts to eradicate or have succeeded and subsequently become re-infected from a neighbouring property. Failure is another reason not to be too keen to try again and many become entrenched Type 3 owners.
Type 3
These are the owners of chronically affected flocks who have been living with the disease on and off for years. They are solidly resistant to any suggestions of eradication, primarily because they have learned to cope and except for extremely wet years, the disease does not cause much trouble. Mostly the incidence of footrot affected feet is low or very low and the costs of eradication are far greater than the disease warrants. When improved pastures are introduced the economics can quickly change; but tradition dies hard. Other long term battlers have found the new footrot vaccines of great benefit, and are happy to maintain control and leave the hazards of eradication to others.
CONCLUSION
The area of R.V.O. Central West has a relatively low prevalence of footrot and a percentage of sheep owners in the area have already achieved eradication. The prevalence could be further reduced by a more concentrated extension campaign and by more effective policing of saleyards and roads and laneways. Action taken at saleyards is frequently the first occasion that an owner is forced to acknowledge to himself that he has a footrot problem.
With new chemical control measures and vaccines the disease can be reduced to manageable proportions on most affected properties and greater activity towards motivating owners to eradicate footrot from their sheep flocks is possible. The grazier community in general would certainly welcome a greater input in this direction.