By Stephen Champion, BSc (Hons) BVM&S MRCVS,
Veterinary Surgeon, CHAMPIONVET.com
Written for Farming Scotland Magazine, Jan 2001

In the first of two articles, Stephen explains the “clostridial” part of the multicomponent sheep vaccines (such as that in Heptavac and Covexin). In a future article, he will explore the “pasteurella” part, for protection against pneumonia and septicaemia.

IMPORTANT ASPECTS OF THE CLOSTRIDIAL DISEASES

Clostridial diseases of sheep were written about by the Ettrick shepherd James Hogg as long ago as 1807, although at the time the cause was not known. The Moredun Research Foundation in Edinburgh was established in 1921 largely as a result of the horrendous losses suffered due to clostridia and had produced the first crude vaccine against braxy by 1923. However, due to the downturn in the fortunes of farming over recent years and perhaps reluctance by some to vaccinate, this group of diseases is again becoming more prevalent amongst the Scottish national sheep flock.

The clostridial diseases recognised in sheep may be divided into the enterotoxaemias, tetanus, braxy, malignant oedema, black disease, and blackleg, showing a variety of symptoms and occurring in different ages of sheep. The bacteria produce highly potent poisons or toxins, which rapidly kill an affected animal. Treatment is almost always unsuccessful and well-planned vaccination programmes are essential to prevent potentially huge losses sometimes over 30% and serious welfare implications. There follows a brief summary of the clostridial diseases, leading on to methods for their control.

The Enterotoxaemias

These are a group of diseases caused by members of the Clostridium perfringens family. They produce in all 12 different toxins, most of them lethal! Lamb dysentery is found in stronger lambs less than 14 days of age, generally at the end of the lambing period. They are usually found dead, but may be noticed just before death with severe abdominal pains or nervous disorders.

Struck is a rare disease not found in Scotland. It was first described in the Romney breed in Kent and occurs only in adults, characterised by abdominal pain and death.

Pulpy kidney disease is the commonest of this group. It can be found in growing and finishing lambs and interestingly as a cause of sudden death in tups when they are being flushed before mating. Sometimes animals may be see alive with diarrhoea and nervous signs, just before death.

The spores of the enterotoxaemias live in the soil and in the faeces of normal animals. The diseases can be triggered off by abrupt changes in feeding routines, such as the sudden introduction of lush pasture or high levels of concentrates. Overeating also contributes and this is why single, greedy lambs often succumb.

Tetanus

The spores of Clostridium tetani usually enter the body through man-made wounds, such as those produced by castration, tail docking or shearing. It can also enter through the navel. The incubation period is three to ten days from when the animal picks up the infection. Unlike the above conditions, the lamb is often found alive and unwilling to move. Within hours it becomes characteristically stiff, exhibits severe spasms and dies.

Black disease

The disease is caused by Clostridium novyi and is associated with liver fluke infestation, usually in older sheep in the Winter months. Movement of fluke through the liver stimulates the development of spores, which release toxins causing massive destruction of the liver. Treatment is of no benefit. Obviously control of liver fluke in sheep by dosing at the appropriate time can reduce risk of losses to this disease.

Braxy

Braxy is caused by Clostridium septicum and is often associated by the consumption of frosted food during the Winter months. It occurs in Autumn and Winter, usually in lambs born the previous Spring. Occasionally it can occur in adult ewes or tups. As with many of the other clostridial diseases, the first signs are a high rectal temperature and abdominal pain, followed by rapid death. Again, there is no treatment.

Blackleg

This disease is known by many names, including black quarter and quarter ill and is caused by Clostridium chauvoei. It is usually brought on by soil contamination of wounds such as those caused by shearing, docking and assisted lambing and symptoms develop rapidly, within two days. There is a high fever and the first thing noticed is an animal that is stiff, apparently lame and unwilling to move. Usually the highly muscled areas of the hind limbs are swollen and very painful and often a crackle can be heard when the affected area is manipulated (a symptom called “crepitus”). Depression and death follow rapidly from this.

Malignant Oedema

Malignant oedema is a rapidly fatal infection usually caused by infection of fighting wounds to the heads of tups by a mixed infection of clostridia. Swelling to the head is seen, together with crepitus and a dark-coloured gangrene. Within 24 to 48 hours, the bacteria enter the bloodstream of the affected animal and death follows rapidly. Unlike other Clostridial infections, this condition can sometimes be cured with antibiotics of the correct type if given at an early stage.

Bacterial Redwater

This is a rare disease of sheep in the UK and is more commonly found in cattle in central Ireland. It is caused by Clostridium haemolyticum and usually affects older sheep during wet Summers. The animal produces dark red urine and the whites of the eyes appear yellow, a sign of jaundice. Sheep die shortly after the onset of these signs and on opening the carcass bloodstained fluid is seen in all the body cavities.

Clostridium sordellii

This is a relatively recently discovered member of the clostridial family, causing an acute abomasitis (a rapid-onset inflammation of the stomach) in young or finishing lambs. Occasionally it can cause sudden deaths in ewes around lambing and rams when being flushed, often affected by rupture of the stomach. It is precipitated by rapid changes of the diet of management. No vaccinal protection is currently available and so control must be by management. Often the provision of carbohydrate-rich concentrate diets to lambs of three to 10 weeks of age should be avoided if this becomes a problem on a farm.

CONTROL OF THE CLOSTRIDIAL DISEASES

Vaccination

By the mid-1970s, multicomponent clostridia vaccines were available and these were combined with pasteurella components in the mid-1980s to give additional protection against pneumonia (covered in a future article). The vaccines are highly effective if used properly and are directed against the toxins produced by the bacteria, rather than the bacteria themselves.

The clostridial vaccines are manufactured by broadly similar processes and no great difference exists between those produced by the two main manufacturers, apart from the volume of dose required. Covexin 7 or Covexin 8 Clostridial Vaccine (Schering-Plough Animal Health) requires 5ml while Heptavac and Ovivac (Intervet UK Ltd.) require only 2ml. An advantage of the Intervet range of vaccines is the option to use the product combined with pasteurella vaccine, such as Heptavac P Plus, thus protecting against pneumonia and septicaemia with a single course of injections. There is also a greater versatility in this range of vaccines.

For sheep of any age, a “primary course” of two injections, four to six weeks apart, is essential. “Booster” vaccinations are required annually, as the immunity wanes and does not provide sufficient protection. This is usually done four to six weeks pre-lambing. One of the ewe’s greatest attributes is her ability to transfer antibodies, and hence protection, to her lambs through her collostrum , or first milk. This fact is exploited in the clostridial vaccination regimes.

Ewes should be boosted four to six weeks before lambing is due. For a long lambing period, it is important to identify late lambers and boost them later at the correct time.

Ewe lambs to be tupped as shearlings should get a primary course, preferably before weaning and should then be included with the ewes for a booster during the pre-lambing period (since they must be boosted at intervals not more than 12 months). They should then receive a booster the following Spring before their own first lambing and every Spring thereafter.

It is important to remember that all breeding sheep vaccination programmes must include tups and tup lambs.

Lambs that have received a good supply of collostrum (from vaccinated ewes) immediately after birth, will be protected by their mother’s antibodies for the first 12 weeks of life. Hence the maternal protection from collostrum, derived ultimately from good stockmanship, is essential for the lamb’s protection in the first few weeks of life.

The choice of vaccine for lambs depends on for what they are intended. Those to be kept for breeding require vaccination against all of the clostridial diseases (by the use of Heptavac, Heptavac P Plus or Covexin). Lambs for early slaughter require protection only against pulpy kidney and tetanus (protection against lamb dysentery in the first three weeks being given through the collostrum). Those aimed at the store market or autumn finishing need protection in addition against braxy, blackleg and malignant oedema. In practice, lambs other than those intended for breeding often receive Ovivac or Ovivac P Plus, the four-in-one clostridial vaccine, provided their dams have been properly vaccinated.

The duration of maternally acquired protection through the collostrum varies according to the disease. Protection against pulpy kidney lasts for up to 12 to 16 weeks, whereas protection against pasteurellosis only lasts for about 24 days. Hence, when combined protection is being used on a farm, vaccination of lambs with Heptavac P Plus or Ovivac P Plus can be started from 3 weeks of age. Straight clostridia vaccines such as Heptavac, Ovivac or Covexin are not required (or recommended) until 8 weeks of age but can be used from 1 week (Heptavac) or 2 weeks (Covexin) of age, in lambs born to unvaccinated ewes.

Management Tools

Prevention of infection by clostridia is fundamental to control. Control of liver fluke using suitable drenches at the appropriate time will help prevent Black disease. Antibiotic treatment following trauma should not be forgotten and hygiene precautions during lambing maintained. The access of every lamb to sufficient collostrum immediately after birth should be aimed for.

Control of an outbreak involves a dual approach of management techniques and therapy. Some outbreaks in young lambs have been controlled with vaccination or antiserum, but this should not be relied upon and should be undertaken strictly under veterinary guidance.

Sometimes removal of the remainder of the flock from a particular pasture or a reduction in concentrate feeding is required. Avoidance of stress factors and the gradual introduction of new feeding regimes may also reduce the likelihood of disease.

Generally the costs of control by management alone are high and of all the sheep diseases, the clostridial diseases are ideal candidates for control by vaccination. For this reason, and to avoid potentially devastating losses, vaccination is highly recommended for most flocks.

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