Sheep & Goats
Contagious agalactiae (CA) is a form of mycoplasmosis. Mycoplasmosis or Mycoplasma is costly for the dairy sheep and goat industry and can lead to incidences of mastitis (inflammation of mammary glands), arthritis (inflammation of joints), keratoconjunctivitis (pink eye), bronchopneumonia (inflammation of the lungs), and abortion among small ruminant animals. It is caused by a microorganism of the genus Mycoplasma.
Although the main causal agent is the Mycoplasma agalactiae, the M. mycoides subspecies capri (Mmc), M. capricolum subspecies capricolum (Mcc), and M. putrefaciens also affect sheep and goats. Mycoplasma ovipneumoniae is associated with bronchopneumonia and produces high mortality in kids and lambs.
Mode of Transmission
The disease is transmitted by the introduction of a carrier into a goat herd or sheep flock. The carriers, animals that are chronically infected that are not displaying symptoms, can infect other susceptible animals in the herd or flock. Symptomless does and ewes may shed Mycoplasma strain mainly in their milk for a long time. Transmission occurs when lambs or kids are nursing. The incubation period ranges from 1 week to 2 months. Studies have shown that for the disease to develop, Mycoplasma spp must invade the host cells and cause further tissue damage. Mycoplasma infection can lead to subclinical mastitis (disease present but not easily identifiable) cases and further develop into chronic cases. The disease can also be transmitted sexually. Asymptomatic buck and ram (no symptoms present) carriers are a concern when it comes to transmitting and controlling the spread of the disease. An infected herd’s morbidity rate (percent of sick animals) can reach up to 90% and mortality up to 30%, respectively.
Sheep flocks and goat herds may experience acute outbreaks of CA and chronic cases are common in some animals. The degree of severity and clinical signs depend on the genetic makeup of the infecting Mycoplasma species. Inflammation of the mammary glands (mastitis), keratoconjunctivitis (pinkeye) and polyarthritis (inflammation of the joints) are the most common signs of CA.
Severely infected animals can exhibit severe lameness due to polyarthritis with hot swollen joints, weight loss and fever. Bronchopneumonia is frequently associated with high mortality rates in lambs and kids that exhibit a cough, shortness of breath, runny nose, loss of appetite, and severe weakness. Abortion can also occur frequently in infected herds and flocks.
Serological diagnosis can confirm a clinical diagnosis. A reliable diagnosis can be achieved by isolating the Mycoplasma strain from the milk of infected does and ewes, or from synovial fluid of animals with polyarthritis, and from eye or nose secretions of pinkeye and pneumonia cases. The ELISA (immunologic test) is commonly used. The complementary immunoblotting test is applied. Polymerase chain reaction (PCR) tests can be applied in the diagnosis of the M. ovipneumoniae. Post-mortem diagnosis can be achieved by isolation of Mycoplasma from the udder, regional lymph nodes, joints, and lungs tissues. Samples must be cooled at 4°C and submitted rapidly to a microbiology laboratory.
Mycoplasma can be treated with antibiotics such as tetracycline, erythromycin, tylosin, or tiamulin. The use of erythromycin and tylosin can destroy milk-producing tissue in small ruminants. Prognosis for complete recovery is guarded. Culling of infected animals is highly recommended.
The biggest challenge is to develop methods of diagnosis capable of accurate detection of chronic and subclinical infections, and the development of high efficacy vaccines to prevent it.
- Avoid purchasing breeding stock from unknown sources. Screen through serology the breeding stock. Sick animals must be isolated from the rest of the flock or herd and culled.
- Apply biosecurity measures: disinfect isolation pens and contaminated materials before mixing with healthy animals.
- Separate lambs and kids from a positive mother at birth, and feed heat-treated colostrum to 56°C for 1 hour. Also, feed them with pasteurized milk or a milk replacer.
- Apply California Mastitis Test to identify does and ewes with sub-clinical mastitis before the treatment.
- Does and ewes with mastitis should have milk samples withdrawn and sent to a diagnostic laboratory for microbiological isolation of the agents, and to determine treatment.
- Keep a closed herd.
- Apply sanitary measures and use a new needle per animal when giving shots.
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