There are several reasons for the occurrence of skin lesions and conditions in sheep and goats. It is usually believed that external parasites are the cause. It can, however, be caused by viruses and parasites or can even be part of other disease complexes.
Sheep scab is an important disease caused by the Psoroptes ovis mite. It causes irreversible damage to the fleece and initially spreads unnoticed in a herd. Once clinical signs are observed, the mites will have already spread.
The mite causes severe itching and irritation, the skin becomes inflamed and pus and scabs form. Outbreaks occur in the winter months. The parasite can be confused with Australian itch mite infestation or with red lice or louse fly infestation, which all cause itching. P. ovis, though, is a notifiable condition and must be treated under the supervision of a veterinarian.
The red louse, Bovicola ovis, is more active in winter. It is large enough to be observed on the animal with the naked eye. Louse infestation results in severe irritation and weight loss. A dip treatment with an agent containing a pyrethroid ten to 14 days apart, or spraying with Expel Plus Jetting Fluid, is an efficient treatment method.
Abscesses and their causes
Abscesses are a fairly common sight on a sheep farm, since the bacteria that cause them occurs in the environment and can survive for long periods. Any wounds, such as those accompanying the management process e.g. tail docking, ear tagging and castration, can become infected.
Sometimes the cause is tick wounds, plant thorns and grass seeds. Grass and weed seeds that stick around the throat and mouth cause abscesses on the tongue and throat area. Due to discomfort and pain, the animals do not feed and lose condition. It also occurs when animals are forced to eat woody or thorny feed, which cause damage to the mouth and throat tissue.
The major cause is Corynebacterium ovis (also called pseudotuberculosis) and Arcanobacterium pyogenes. C. ovis is commonly associated with the shearing process.
Effective vaccines are available to curb the infection in mature animals and prevent it in young animals. Good hygiene is crucial, and wounds must be treated with a disinfecting spray such as Expel Wound Spray (G3245, Act 36/1947) or Futa Spray (G2715, Act 36/1947) as soon as possible.
Prevent pus from the abscess from infecting the environment. Instruments must be disinfected thoroughly to avoid transfer. Ensure that new animals brought to the farm are immunised against C. ovis. A veterinarian must treat A. pyogenes intravenously.
Some blowflies have adapted to the environment and under certain conditions lay their eggs on live sheep. The problem is more common in fine wool sheep such as Merinos, when the fleece is fouled by manure and urine or if they are subjected to wet conditions for a long period.
The wet skinfolds make certain animals more susceptible since it leads to localised fleece rot, involving breaking of wool and the fleece becoming soft. The accompanying smell attracts blowflies, which then lay eggs in these areas. When the eggs hatch, larvae appear that feed on the tissue. Large open sores form, the animals become restless and can even die if the wound remains untreated.
Wounds must be cleaned thoroughly and an insecticide containing deltamethrin, such as Expel Wound Spray, is ideal to simultaneously treat the blowflies and the wound. Sheep can be preventatively treated with Expel Plus Jetting Fluid (G4027, Act 36/1947), which contains an insect growth regulator and ivermectin.
Fleece rot entails the growth of the bacterium Pseudomonas aeruginosa on wet wool. In contrast to lumpy wool where a hard scab forms, fleece rot is a wet infection. There is no treatment, such as antibiotics or something similar, against it. The best solution is to disinfect the affected areas and to dry them out by shearing the wool.
Lumpy wool or dermatophilosis is caused by the bacterium Dermatophilus congolensis. It can affect sheep, goats, cattle and horses. The presence of sheep infected with D. congolensis serves as source of infection of other susceptible animals in the herd. The disease is spread if the climate is humid and wet and if there is close contact between animals.
If animals become wet, such as during dipping, the chances of spreading increase. Usually, animals are put in a kraal for a considerable period after the dipping process, which causes animals to become infected due to their close contact with each other. D. congolensis can survive for up to four months away from the animal. Dip holes without added zinc sulphate are often a source of infection.
Lambs are born without wool fat and it takes four to five weeks before the protective wax layer forms on the skin. The result is that lambs are extremely susceptible to lumpy wool.
Lesions occur where the germs penetrate the skin. Where sheep are exposed to extremely wet conditions, for instance, the lesions usually occur on the back since the wool remains wet. Sheep feeding on thorny shrubs get small wounds in their mouths and on their legs and coronary bands through which the bacterium penetrates.
Forms of lumpy wool
- Common form: The lesions form pus and the sticky bodily fluid cakes the wool together and scabs (so-called lumps) form. Below the lump the skin is raw and cracked and a bleeding wound remains if the wool is removed.
- Hardelamsindroom: When wool sheep lambs are born in the rainy season, they remain moist. The whole back, neck and even ears form hard scabs. Lesions can also form on the head and lips. Lambs are sick, feed and drink poorly and can even die.
- Dorpers with lumpy wool can lose their entire hair and wool cover. They can die due to exposure.
- Ear and face lumpy wool: Bloodsucking insects play a role in the occurrence of lumpy wool on the face and ears. It is often incorrectly attributed to sunburn. This condition must be distinguished from scabby mouth, which is a viral infection.
Your local veterinarian can take a wool sample, colour it and identify the bacterium under a microscope. Samples for a culture can be sent to a laboratory for identification. Topically applied zinc sulphate will help to treat the condition.
Scabby mouth (Orf)
The scabby mouth virus can infect the udders of ewes and the mouths of lambs. The virus causes raw wounds with scabs. Ewes and lambs must be immunised to avoid the disease.
Certain poisonous plants cause infection of the skin when the skin is exposed to sunlight (photosensitivity). The skin becomes red, raw and peels off. The face sometimes swells up in early cases. Secondary bacterial infection can occur because the skin is exposed.
Tribulosis (geeldikkop) and dikoor, which are respectively caused by devils’ thorn (duwweltjies, Tribulus terrestris) and common Buffalo grass (Panicum spp.), are the major cause of small stock losses in South Africa – there are an estimated 74 000 mortalities annually.
The photosensitivity caused by poisonous plants can only be treated symptomatically. Animals should be kept out of the sun, wound oil can be applied to the skin to keep it soft and, if necessary, antibiotics can be administered in the case of secondary infection.
Source: Diseases and Parasites of sheep and goats in South Africa by Pamela and Peter Oberem. For more information, phone Afrivet on 012 817 9060 or visit www.afrivet.co.za.