Health Problems and Diseases that are of Particular Importance for Persian Breeders
Worms. Worms are the most common cause of disease in Australia in sheep. There are 4 common types of nematode worms found in sheep in Australia. In these common types, adults live in the digestive tract of sheep. These adults release eggs that are passed in the sheep droppings. After a period of time- usually days to weeks, on the pasture, the eggs become infective and if then ingested by sheep while grazing are able to hatch in the digestive tract. The larvae that hatch from the eggs eventually mature to adult worms that in turn produce further eggs that are then passed in the droppings. In this way there is ongoing contamination of the pasture with fresh worm eggs. And the number passed can be amazing. Sometimes 10, 000 or more can be found in a single teaspoon of droppings. Worms compromise health by interfering with the bowel and stomach’s ability to efficiently absorb and assimilate nutrients and also by damaging the bowel and stomach lining that can then bleed and leak tissue protein. All sheep on pasture have worms. Symptoms vary depending on the type of worm and the severity of infection. Sometimes the sheep may just be failing to thrive. Often the main symptom is diarrhoea , for example with Trichostrongylus (or black scour worm). Sometimes, however there may be no diarrhea as is the case with Haemonchus (or Barbers Pole worm ) where bleeding from internal stomach ulcers leads to pale gums, general weakness and swelling in the legs and jaw. Even if worms are not the beginning and end of a problem they often are part of a problem and should always be considered when sheep appear weak, are thin or simply failing to thrive or have diarrhea. Your sheep veterinarian can examine your sheep droppings and tell you what type of worms are there and how many there are present.
Often what happens , particularly in low stocking and pet situations is that growing sheep are exposed to low numbers of worms as they mature. This ongoing low grade exposure may not lead to disease but allows the developing sheep to build up a natural immunity to the parasites. Disease comes either through high exposure or rather an exposure than the animals immune system cannot handle or if there is an error in the flocks management that weakens the animal and makes it more vulnerable to disease generally. This error most commonly is poor nutrition, however anything that weakens a sheep such as persistent cold or damp conditions may be involved.
When worms are a problem the immediate thing to do is worm the sheep. This however is likely to provide only a short term solution as sheep placed back on the same pasture will immediatey become reinfected and as the life cycle of most worms is completed in several weeks this means that within this time the sheep will once again be unwell.
Effective control of worms requires planning. To some extent the fact that sheep develop disease associated with worms means that inadequate planning has taken place. The first thing to do is to make sure that the sheep are generally well cared for so they are at their best to resist disease generally. The next thing is to decrease exposure to worm eggs principally through pasture rotation. What this means is that rather than letting sheep graze over an entire area, access to certain paddocks should be prevented at certain times. Doing this means that many of the worm eggs will die before there are sheep grazing again on that area. In this way potential for re-exposure and re- infection is reduced. Rotating every 6 weeks or more is often best and practical. The third thing is to strategically worm the sheep. Simply worming sheep again and again can actually be harmful. It encourages the development of worms that are resistant to worm medication and can fail to allow for the low grade ongoing exposure required for sheep to develop immunity to the worms. During hot dry conditions most worm eggs only survive on pasture for about 6 weeks. During cooler , wet times eggs can survive for many months. Recommended worming protocols vary from area to area but in the high rainfall area of southern Victoria, where I live, it is much more effective to give one or two drenches during our hot Summer usually about 6 weeks apart. Because of the hot, dry conditions at this time , most eggs on the pasture have died leading to a low re-infection rate and prolonged benefit. Lactating ewes pass large numbers of eggs and can expose their lambs to high levels of infection. Sometimes worming ewes during pregnancy can therefore also be beneficial. Effective worm control can be complex. Your local sheep vet will be able to advise what is best in your area.
Footrot and Scald Nature of the disease. What is Footrot? Put simply, Footrot is a bacterial infection of the feet of sheep. Two bacteria are involved, Fusobacterium necrophorum and Dichelobacter nodosus. Even though it may seem straightforward to manage an infection these days, the disease that these bacteria cause is complex, highly contagious and at times difficult to control.
The first bacteria, Fusobacterium, is a widespread bacteria that is found in soil. Simple exposure to the bacteria does not cause any problem, however, if something compromises the skin’s ability to resist infection, Fusobacterium can take advantage of this situation and invade the skin, causing an infection. Persistent exposure to wet conditions is the most common predisposing factor, however, anything that damages the foot can make a sheep more vulnerable. Walking on rough irregular surfaces and even coarse or prickly vegetation has the potential to abrade the skin and has also been implicated. Ongoing exposure to damp conditions superficially macerates the skin and gives Fusobacterium an opportunity to invade. When Fusobacterium invades, it causes inflammation of the skin between the cleats. Here it is warm and protected and the skin is more likely to be persistently wet during wet conditions. The condition caused by Fusobacterium is called Scald. The name is apt because the infected area of skin looks as if it has been scalded by hot water. The skin between the cleats becomes pink, moist, swollen, painful and may be covered by a grey/white fluid. The infection is, however, usually odourless. Scald is not invasive, and causes no separation of the horn from deeper tissues.
The disease called Footrot develops when the second bacteria Dichelobacter becomes involved. Like Fusobacterium, Dichelobacter cannot invade the skin without prior damage to the foot. However, once Dichelobacter invades, it has the potential to cause much more severe disease. Multiple strains of Dichelobacter occur, which vary in the severity of the disease that they cause. With mild strains, the disease may look just like Scald. With more severe strains, the infection can invade the soft tissues of the foot. This can progress in the most severe cases to where the infection extends between the outer hoof and flesh of the toe, lifting the hoof away from the underlying structures. The hoof can separate and be lost. Animals with mild lesions tend to remain in good condition but just limp. However, as the severity of the infection increases, so does the pain. More severely affected animals become reluctant to graze and loose condition. In the most severe cases of Footrot, the appearance of the lesion can be diagnostic, however, in milder cases it is not possible to tell simply by examination whether the problem is an uncomplicated Fusobacterium Scald or a mild case of footrot with Dichelobacter involved. Diagnosis is reached by taking a swab from the infected area and then forwarding this to a veterinary diagnostic laboratory, where the actual bacteria involved are identified.
The interplay of the two bacteria is still unclear. It is known that preventing Scald helps prevent Footrot. Two suggestions have been made for the role of Fusobacterium in the Footrot complex. Either Fusobacterium is important to establish an interdigital dermatitis before Dichelobacter can invade and hence initiates the disease or alternatively Fusobacterium is involved in the persistence and severity of Footrot, once the under-running lesion has developed, playing a role as an opportunistic, secondary disease organism. What is likely is that the damage to the skin from Scald allows Dichelobacter to invade and colonise deeper layers, where it feeds on collagen. Once Dichelobacter is established, Fusobacterium can advance deeper into tissues, too, where it contributes to further inflammation and tissue damage.
Treatment and Control Scald cannot be easily eradicated from the flock because the causative bacteria F. necrophorum occurs naturally in soil and therefore cannot be eliminated. In contrast, Footrot can be eliminated from a flock because D. nodosus does not survive in soil for long periods. Dichelobacter is fragile in the environment and can only survive for 2-3 weeks on pasture even under optimal moisture and temperature conditions. Dichelobacter can only persistently survive in the warm, moist, dark nooks and crannies on the feet of sheep. These facts mean that although any sheep on any property at any time have the potential to develop Scald, sheep have to actually catch Footrot and they can only do this either by sharing ground with sheep that are carrying Dichelobacter or being placed onto pastures where sheep with Dichelobacter have been in the last 3 weeks.
With Scald, it is important to match the degree of intervention with the severity of the problem. Keeping feet as clean and dry as possible by avoiding muddy areas, particularly during persistent wet weather, will do much to decrease the problem. If despite this, a small number of sheep develop Scald, they can be treated individually by spraying their affected feet with either coloured oxytetracycline (antibiotic) spray or antiseptic sprays such as Cetrigen, provided the treated animals are not immediately returned to wet grass. If there are larger numbers affected, this becomes impractical and the only manageable way to disinfect the feet is through foot bathing. Over the years, the best and most cost-effective conventional method for the control and prevention of Scald (and Footrot for that matter) has been regular foot bathing. As Scald infection is superficial, the animals do not have to stand in the footbath for very long. Walking sheep through foot baths 6 m long, 10 cm deep containing 10% zinc sulphate heptahydrate is adequate.
The approach to Footrot treatment and control is quite different to that of a Fusobacterium Scald. Footrot is an infectious disease and an attempt should be made to eradicate Dichelobacter from the property. Fortunately Dichelobacter is a fragile organism. It is readily killed by dry heat, sunlight, cold and a dry environment. Because of this, Summer is the best time to attempt eradication. In flocks with Footrot bacteria present, lameness is more likely to be noticed during the wetter times of year when conditions favour the growth of the organism. The incidence of lameness naturally reduces through the hot dry times of the year and even though the animals are less likely to be lame then, this is, in fact, the time to attempt to eradicate the disease.
As outlined above, Dichelobacter can only survive in two places, either on the pasture for up to 3 weeks or on the sheep’s foot. Control of Footrot aims to kill the organism in both of these areas. Eradication from a pasture is easy to achieve. Simply spelling a paddock by not allowing sheep to graze on it for 3 weeks results in eradication of Dichelobacter from that paddock. To eradicate Dichelobacter from a sheep’s foot, however, is much harder. There are four common methods available. 1/ Foot trimming. Dichelobacter likes the warm, moist nooks and crannies found in sheep feet. At one time, it was recommended to routinely trim overgrown cleats and remove separated horn material to eliminate areas where the bacteria could potentially survive. It is no longer recommended to routinely trim diseased and healthy feet as it has been shown that, unless done with extreme care, this can damage the foot, in the process exacerbating Foot-rot and Scald. Similarly, it is no longer advised to trim the hoof horn into the dermis (second layer of skin), as it may lead to granuloma (a thickened area of scar tissue) formation. However, routine inspections and careful trimming are advised in cases where there is loose horn that may allow mud and debris to get stuck in the foot. If foot trimming is necessary, the clippers should be sharp and disinfected between feet to minimise the spread of any bacteria. Bacteria can be spread from one animal to another on dirty clippers. It is also important to collect and dispose of any hoof clippings as they can be a source of infection with Dichelobacter being able to survive in them for up to 6 weeks
2/Foot bathing. Foot baths are prepared by diluting astringent/antiseptic agents such as 10% zinc sulphate heptahydrate in foot baths. In the case of Footrot, the animals need to stand in the foot bath much longer (10-15 minutes) than is necessary to treat Scald. After foot bathing, sheep should stand on a hard surface for an hour to let the feet dry. Treated animals should be turned out onto pasture that has been free from sheep for at least 3 weeks.
3/ Antibiotics. Individual severe cases of Footrot should be promptly identified and treated individually with injectable antibiotics and coloured oxytetracycline sprays. Long-acting oxytetracycline is very effective in treating the disease and requires less handling than short-acting oxytetracycline. Usually long-acting injections that last for 3 days are given. These are repeated on a needs basis. This more intensive treatment is particularly important in managing individual sheep of value and severely affected sheep. Other antibiotics are also used. Your local sheep vet will be able to advise here.
4/ Vaccination. Footrot vaccine has only become available comparatively recently in Australia and it has been a ‘game changer’. Property-specific vaccines are prepared against the Dichelobacter strains identified on a property. After vaccination, antibodies produced as a result of the inoculation inhibit Dichelobacter invading the soft tissues of the foot. Different strains of Dichelobacter occur on each affected property. It is therefore important that the actual strain(s) on a property are identified so that the vaccine can be specifically prepared against these. To do this, either preferably your local vet or you under veterinary guidance will need to collect swabs from the feet of your sheep. Initially, lame sheep are separated and examined. If they are found to have Scald or other lesions consistent with Footrot, a swab is collected from the interdigital area and also from any other area that looks infected. These are forwarded to Sydney University where the type(s) of Dichelobacter present are identified. Once known, these results are forwarded to the vaccine manufacturer (Treidlia Biovet) in Sydney where the vaccine is made. This may sound complex and expensive but it is not and in my opinion well worth it. Once the vaccine is prepared, each sheep is vaccinated by an injection under the skin. A second injection can be given several weeks later if indicated. I have been personally involved as a veterinarian with the use of this vaccine in several properties. The results are extremely impressive. The vaccine stimulates the production of antibodies against Dichelobacter. These are then incorporated in the blood and inflammatory fluid that come in contact with Dichelobacter on the feet, actively fighting the infection. In the flocks I have personally dealt with, vaccine use has led to virtually a 100% reduction in the problem. Treidlia does, however, advise that vaccine use should be combined with other Footrot control measures.
5/ Genetic Resistance .All breeds of sheep are able to contract Footrot, although it has been suggested that some of the more primitive breeds, such as the Soay, are less susceptible. Popular breeds used in Australia and New Zealand, such as Merinos, are highly susceptible. African breeds such as the Persian and Dorper are also susceptible, having been developed in hot, dry conditions where there has been no selection for Dichelobacter resistance. Within breeds, certain lines, families or individuals can be identified as being less susceptible to Footrot. Long-term genetic selection can make a flock less vulnerable to the disease. It is worth noting that the most likely source of a Footrot infection is sheep that are brought onto the property. This should be considered before the introduction of any sheep. Transmission from one sheep to another always occurs via the surface on which the sheep stand. This has relevance in any situation where sheep from different properties come together, such as saleyards and shows. Most show officials are aware of this and endeavour to maintain communal areas as clean as possible.
Involving the Vet Some sheep owners, particularly of smaller flocks, are sometimes hesitant to contact a vet. Owners, however, are encouraged to contact the local sheep vet right from the start of any lameness problem. It is not possible to tell simply by visual examination whether a Scald lesion is caused just by Fusobacterium or whether Dichelobacter is also involved. Only collection of a swab and laboratory testing can tell. It is important to distinguish between these two as control is so different. Obviously, not all cases of lameness are due to Scald or Footrot. Conditions such as shelly toe, toe granuloma, foot abscess and CODD ( Contagious Ovine Digital Dermatitis) can all look very similar. Also your vet will also be able to guide you through the Footrot vaccination process if, in fact, that becomes necessary.
Johne’s Disease. Johne’s is the disease that you don’t want to have. Uncommon 30 years ago it has now become one of the most prevalent diseases in some areas of Australia. Caused by the microorganism, Mycobacteria paratuberculosis it is passed in the droppings of sheep and contaminates the soil and indeed anything that comes in contact with droppings from infected sheep. When ingested during grazing it invades the bowel wall causing thickening and scarring. As this process progresses the bowel become increasingly non- functional, losing its ability to digest food and absorb nutrients. The result is that an infected sheep progressively wastes. Diarrhoea sometimes occurs and in hair breeds such as the Persian a “bottle jaw” becomes visible as a result of fluid developing below the jaw due to the associated hypoproteinaemia ( low protein in the blood ) . Eventually animals become too weak to graze and collapse in the paddock and die. There is no treatment.
Control focuses primarily on vaccination. The vaccine will stop sheep that do not have Johne’s from catching the disease in about 95% of cases. If sheep already have the disease it will not treat them, (although if the vaccine is given to sheep that are already infected it does appear to slow the progression of the disease in some cases). Lambs born into a contaminated environment are vulnerable to infection and the aim is to give the vaccine as young as possible (but old enough for the vaccine to work) and hopefully before the lamb is infected. The recommendation is that lambs are vaccinated as soon as possible after 4 weeks of age. A single vaccination confers life time immunity. Lambs vaccinated in this way are classified as approved vaccinates and can be ear tagged with approved vaccinate NLIS ear tags which are embossed with a large V.
The time to vaccinate against Johne’s is before the disease gets onto the farm. Once there are sick sheep and deaths many of the sheep will already be infected. The effect on the flock can be catastrophic. If the disease is already on the property then vaccinating the lambs at 4 weeks of age each year will see a gradual reduction in clinical disease as the older sheep die or are culled and the majority of lambs each year are approved vaccinates and develop protective immunity. To eradicate the disease, if indeed this is possible, is likely to take many years.
Ovine Brucellosis Brucellosis is a bacterial infection of the genital tract in sheep. It is spread from ram to ewe and from ewe to ram through mating and also from ram to ram through sodomy. Caused by the bacteria Brucella ovis, in rams the bacteria damages the testes and epididymus leading to palpable lumps and other abnormalities within the scrotum and causing either a reduction in fertility or sterility. In ewes infection of the uterus can lead to abortion. The significance of the disease is the reduced conception rate and also the loss of lambs that are conceived through abortion. Ewes do not carry the infection from one Spring to another and so simply not breeding from them for 12 months means that they will be clear of the infection. It is the rams that are the long term carriers of the disease and infected rams infect ewes and other rams. In some parts of Australia, for example the Mallee in Victoria, the disease is common. Your sheep vet can test rams through physical palpation of scrotal contents, examination of semen and through a blood test that checks for exposure to the disease. Preventative measures include only sourcing rams from OB free flocks, having a sheep veterinarian examine and test rams prior to entry and having good boundary fences. If present on a property the aim should be to eradicate the disease. This can be achieved through a protocol involving examination, blood testing and culling of positive animals. Dermo Dermo is a bacterial infection of the skin caused by the bacteria Dermatophilus congolensis. Clinically affected Persians develop flat , grey , crusty plaques on the face and ears. Dermo does not readily become established on dry healthy skin. For infection to occur the waxy layer on the skin must be broken. In Persians this occurs if the skin remains wet for 3 or more consecutive days so it becomes macerated. Most dermo infections start during winter with skin damage due to persistent wetting. Most affected animals are weaners and it tends to be the less robust animals that are more susceptible. Most infections self resolve with time and the start of warm dry weather. If necessary antibiotics , as prescribed by you local vet can be used to treat the more severely affected individuals.
Young Persian with “Dermo”
General Health and Disease Guide “ Sheep Diseases, The Farmers Guide”. An extremely useful summary of sheep health issues written for the farmer can be found on line titled “ Sheep Diseases, The Farmers Guide”. Originally produced by PIRSA in South Australia, it is written by Dr Tony Brightling, a sheep veterinarian and author of the book “Sheep Diseases” . It is an extremely useful and practical reference written in straightforward language and gives practical advice. As always your local sheep veterinarian and DPI office are the best people to contact when health issues arise.