Sheep Diseases
Diagnosis, Treatment and Prevention
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Improving and maintaining the health of our flock is a priority as disease can dictate whether the flock succeeds or fails. In addition, eradication of several common diseases, discussed below, is often possible when flock size is small.
FOOT ROT - is a serious disease caused by two bacteria. The first, Fusobacterium necrophorum, is commonly found in the soil and feces. The second, Dichelobacter nodosus, is the primary cause of foot rot and is found in diseased sheep and goat feet, or in areas recently contaminated by infected animals. There are 17 different strains of D. nodosus which vary in their ability to cause foot rot. The bacteria can live in the soil for 2 - 3 weeks and in the hooves of some sheep for months. Chronic infection can lead to decreased food intake, poor fibre and milk production and deformed hooves. Rams affected with footrot may not be able to work or in severe cases may have decreased fertility.
Diagnosis - the infection starts between the toes and eventually undermines the sole and hoof wall. Animals may have one or more affected feet. Problems range from small areas of infection/inflammation that are only detectable by careful inspection, to animals that limp, walk on their knees or do not walk at all. A characteristic, fetid odor is often present.
Treatment - Choice of treatment regimine will depend in part on whether control or eradication is sought. In general, the most effective treatment protocals utilize multiple modalities.
Sheep should be tipped up so that the feet can be fully visualized. A sheep "sofa" or a tire can facilitate this task. The whole flock should be carefully inspected for signs of foot rot. Be conservative in your assessment because bacteria may survive walled off in the hooves of some sheep without external evidence of their presence. Be suspicious that there are hidden pockets of infection when hooves are rough, irregularly shaped, or when the foot seems tender. "Clean" animals can be released to graze on pasture that not been grazed for at least 3 weeks. Infected animals should be isolated and treated until assymptomatic.
The hooves of infected animals should be trimmed to expose areas of infection. Avoid causing bleeding and clean the hoof shears with zinc sulfate solution between sheep to prevent the spread of infection.
Following trimming, the feet should be soaked in a bath of 10% zinc sulfate (8 lb. to 10 gallons of waters) for 20 - 30 minutes. Add 2/3 cup of laundry detergent to help the mixture penetrate the hoof. The footbath should be repeated once or twice weekly until the disease is controlled. For a small flock, it may be more practical to spray zinc sulfate in the same concentration on the hooves daily until assymptomatic (mix approximately 1 3/4 cup zinc sulfate with a splash of detergent in 1 gallon jug warm water). I have found that a 3 pint pressurized sprayer works very well for my flock of 50 sheep. Following treatment, the animals should be released onto clean pasture.
Injection of long-acting antibiotics may benefit sheep with severe undermining. However, this treatment is expensive for large numbers of sheep, and is not always 100 percent effective. Footrot vaccines also maybe helpful as a treatment. The usual schedule consists of 2 doses given SQ behind the ear 4 to 6 weeks apart. The first dose is normally scheduled approximately 2 weeks before an outbreak is anticipated. Vaccines have been found to be most effective when used in conjunction with other treatments.
If eradification is desired, culling of chronically infected animals should be considered because genetic selection for resistance to foot rot has been established.
Prevention - The route of spread is from infected sheep, to moist soil and then to non-infected sheep. Prevention strategies aim to break this cycle. Most owners acquire footrot in their flock by buying it. Therefore, the primary prevention strategy involves getting an honest history of any flock from which you purchase sheep. Assume all sheep you purchase have footrot and isolate (2 - 4 months) and examine sheep before introducing them to the rest of your flock. Clean or avoid facilities where sheep with footrot have been kept. And finally, manage your sheep so as to provide routine and appropriate foot care, to prevent injuries to their hooves and to prevent muddy conditions.
References -
Bagley, Clell V. (1998). Contagious Foot Rot of Sheep - An Update.
Henderson, David C. (1997). The Veterinary Book for Sheep Farmers. Ipswich, UK: Farming Press.
Kal, Kim. Rotten Spring.
OPP (OVINE PROGRESSIVE PNEUMONIA) - is a slowly progressing disease caused by a retrovirus. OPP is somewhat of a misnomer as the lungs are just one of many organ systems that can be affected. The virus exerts its effect by infecting and interfering with the macrophages and lymphocytes of the immunologic system. The disease usually occurs in sheep that are two to four years of age and lasts for several months to a year, terminating with the death of the animal. There is evidence that not all breeds of sheep are equally affected by the disease.
Diagnosis - Making a diagnosis based on the presence of clinical signs and symptoms is difficult. Sheep that are affected with the disease often exhibit a wide range of nonspecific clinical signs such as weight loss, difficulty breathing, arthritis, mastitis, and neurologic syndromes. In addition, in the early stages of infection, or when a sheep is a "carrier," no signs of disease may be apparent.
Two serologic tests, an AGIDT and an ELISA test, are currently the most practical ways to detect OPP. A positive test result indicates that the animal animal carries antibodies to the OPP virus. However, the tests do not distinguish between sheep that have passive antibodies (antibodies obtained via colostrum in the absence of infection) and those that have active antibodies (produced by the animal itself in response to infection by the virus). False results can occur in lambs under 6 months of age and in ewes immediately following lambing and shortly before death.
Treatment - There is currently no treatment, other than symptomatic, for OPP. Sheep with OPP are infected for life.
Prevention - Since no treatment is available, those interested in eradicating OPP must focus on preventing its spread. The OPP virus is transmitted by colostrum, milk, nasal secretions, needles and surgical equipment. One means of eradicating the disase is to test and either cull or isolate all seropositive sheep and their lambs under one year of age. These two steps should be repeated every 6 months to a year until two consecutive annual negative flock tests have been obtained.
A second method of eradicting the disease from one's flock involves removing lambs from ewes before licking or nursing and keeping them isolated from infected sheep.
Only the following classes of sheep should be added to the seronegative flock:
- sheep from a seronegative flock
- sheep from seronegative parents in an infected flock, after keeping isolated for one year with negative test results
Periodic testing should be done to ensure that the disease has not been reintroduced into the flock. Additional preventive measures include:
1. Keeping the flock isoated from infected equipment and people
2. Grazing sheep rather than keeping them in confinement type facilities
3. Using aseptic technique when vaccinating or drawing blood from sheep
References
Ovine Progressive Pneumonia. http://www.sheepusa.org/resource/shopp.htm
Smith, B, Aseltine, M. & Kennedy, G. (1997). Beginning Shepherd's Manual. Ames, Iowa: Iowa State University Press.
Smith, Mary C. (1999). Ovine Progressive Pneumonia.
CASEOUS LYNMPHADENITIS (CL, CLA, Cheesy Gland, Abscesses, Boils) - CL is a chronic, infectious disease of sheep and goats caused by the bacterium Corynebacterium pseudotuberculosis. The organism enters the body through wounds, or by being inhaled or ingested, and is carried by the lymph system to the glands where it causes absesses. CL is the third most important cause of condemnation at slaughter. In addition, it may decrease pelt value, adversely affect wool growth and value, reduce milk production, weight gain, and reproductive efficiency. CL is also a health risk for humans who skin affected animals by hand or who drink raw milk.
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