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This article was published in 1989
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Suppurative Polyarthritis
Bill Hetherington, Veterinary Inspector, MOREE
INTRODUCTION
Very significant production losses from suppurative arthritis have occurred at times in the Bullarah area West of Moree.
The severe losses appear to be confined to the more flood prone soils, although not exclusively.
The following is a history based on my and grazier observations along with laboratory histopathology and bacteriology over the last 8 years.
HISTORY
According to local graziers, losses from suppurative polyarthritis have been a feature of the watercourse area for many years, but the 1980's have seen a dramatic increase in the numbers of sheep lost from these infections, most probably due to the number of wet winters during this period.
The majority of producers have losses in the order of 1-3% of total lambs marked but in extreme cases up to 20% of lambs are lost to polyarthritis in individual paddocks and a number of producers have reported total losses of up to 10%.
The incidence of the disease appears to have a direct relation to wet weather, especially prior to mulesing at lamb marking. The wet winter of 1988 resulted in the most severe losses seen since 1983, which was also a wet year.
Graziers that do not mules at lamb marking may still lose a few lambs from infections of the marking wounds but the losses are very light (2-3 hd per thousand).
CLINICAL SIGNS
The clinical signs develop within 1 to 2 weeks after marking and mulesing.
The first indication that the grazier will notice is the mules wound is not healing properly and fly strike will be a problem. This results in a muster to check the fly problem and the realisation that a proportion of the flock has severe lameness.
On close examination the producer will notice that the mules wound will have a yellowish pus draining to the lower parts of the wound.
The suppurative arthritis is more common in the shoulder joint but may affect a number of joints and in severe cases abscesses are noticeable in soft tissue, particularly in the shoulder.
The site of the abscess will vary from barely palpable to the size of a cricket ball and visible from 100 yds.
As the disease progresses the lambs become lethargic and find it difficult to feed and water.
The majority of lambs will die within a few weeks. The proportion of lambs that die depends on the age at which they are marked/mulesed, the younger lambs rapidly die. Some older lambs may survive but will not be of any economic use as the deformity is permanent. Paralysis in the hind limbs has been noted in the odd lamb as a result of spinal abscess.
POST-MORTEM FINDINGS
The joint is grossly enlarged, distorted and full of creamy yellow pus that is frequently foul smelling. There is a great destruction of the joint tissue and in advanced cases sometimes ankylosis of the joint occurs. Abscesses can be found almost anywhere but most commonly in soft tissue in the shoulder, hind leg, lungs and liver.
Many samples including a number of live sheep have been sent to the Armidale Regional Laboratory for identification and sensitivity tests.
MICROBIOLOGY
The most prominent organism isolated has been Fusobacterium necrophorum ranging from a pure culture in the joint and soft tissue abscesses, to a mixed growth containing many organisms including Corynebacterium pyogenes, Streptococcus bovis and Staphylococcus aureus.
The bacteria are sensitive to penicillin, sulfamethoxazole/trimethoprim and tetracycline.
PREVENTION
Producers have adopted many ways to avoid the losses. The most prevalent means used to avoid losses is to cease mulesing at marking and mules as weaners.
This management change has a downside as it increases labour requirements and exposes the unmulesed lambs to flystrike for the first summer, thus leading to further management difficulties, however it does reduce losses from polyarthritis.
The older lambs appear to have less trouble with arthritis probably as a result of a more mature immune system at 6-8 months than they have at 6-8 weeks. Mulesing as weaners does not eliminate the losses but they are greatly reduced.
One producer has used a long acting penicillin as preventative to reduce the losses (1 ml/hd, cost approximately 12c/hd). This appears to have been successful as he has no arthritic lambs. I am not convinced that it is a suitable long term solution.
With the trend away from the use of antibiotics as a management procedure and not (sic) chance of a vaccine in the short term, I think that the change in management is the only way to go, although it is not without cost.
DISCUSSION
Fusobacteria are a normal inhabitant of sheep dung and is the casual organism of foot abscess, as well as the most common organism involved in suppurative polyarthritis in the Moree area.
Moisture appears to be a critical factor in polyarthritis as well as foot abscess. Both appear to be more prevalent in the winter/spring period after a wet season when moisture is present for long periods due to long grass and heavy dew.
With foot abscess the water maceration of the interdigital space is necessary for penetration of the intact skin by the organism. In the case of suppurative polyarthritis the wound is the obvious point of penetration but a moisture triggering mechanism still seems to be required for the bacteria to cause severe losses due to polyarthritis.
In dry winter/spring conditions the incidence of suppurative polyarthritis is at its lowest although losses of small numbers of lambs still occur.
The adoption of hygienic technique at marking/mulesing does not appear to have a direct correlation with the incidence of the disease as great variations occur between different paddocks although lambs are marked at the same yards by the same operators.
A notable case history from the Burren Junction area points to the probability that sheep camps are a major source of contamination that has previously been overlooked. This producer marked and mulesed his lambs from one grazing paddock through the one set of yard on the same day.
The ewes and lambs were brought in, in two mobs of approximately equal size, and the second mob was introduced to a stubble paddock for a month.
Within a few weeks 2% of the lambs in the grazing paddock was affected. The only difference between the treatment of the mobs was that there are not sheep camps in a cultivation paddock. I have strong suspicions that regardless of hygienic technique adopted at marking/mulesing it all comes unstuck when the lamb lies down in its favourite heap of dung in sheep camp.
Many comments have been made that particular paddocks appear to be bad arthritis paddocks. These paddocks appear to be heavy soil, flood prone paddocks where sheep camps are often very few and in constant use, leading to the probability of greater contamination. The heavier soil paddocks also have heavier stocking rates leading to a greater concentration of sheep in the camps particularly in good seasons and after wet weather.
Large losses have been noted where it has been raining shortly before, during or within 24 hours after marking and mulesing. This may be due to the washing of bacteria into the wound and or the retarded healing of mules wound due to the presence of moisture.
The fact that large losses can occur without rain leads me to think that although rain exacerbates the problem it is not essential to cause the arthritis.
FUTURE ACTION
Further observation and sampling will be necessary to try to determine the relative importance of the various factors influencing the severity of the problem, also to more accurately identify the mechanisms and organisms involved in the disease.
With this in mind a group of graziers has been formed to enable close monitoring of future outbreaks.
CONCLUSION
Much more information is needed before a general across the board recommendation regarding prevention of the disease can be given. At this stage I am giving some recommendations on a property to property basis to suit the individual graziers.