Mycoplasma Infections in Sheep: Pneumonia, Mastitis, and Joint Disease

Mycoplasma infections in sheep are contagious bacterial diseases caused by several Mycoplasma species. These organisms are unusual because they do not have a normal cell wall, which affects how they spread, how they are tested for, and which antimicrobials may or may not help. In sheep, the best-known syndromes are pneumonia, mastitis, and arthritis or joint disease. Some flocks may also see conjunctivitis, reduced milk production, poor growth, or chronic unthriftiness.

One important sheep and goat syndrome is contagious agalactia, most often linked to Mycoplasma agalactiae. Merck Veterinary Manual describes mastitis, arthritis, and conjunctivitis as classic signs, while respiratory disease can also occur. Another organism, Mycoplasma ovipneumoniae, is strongly associated with respiratory disease in sheep and can set animals up for secondary bacterial pneumonia.

These infections can look different from one flock to another. A lactating ewe may mainly show udder changes and milk loss, while a lamb may show coughing, fever, or swollen joints. That variation is one reason flock-level planning matters. Your vet may focus not only on the sick sheep in front of you, but also on transmission, chronic carriers, and long-term production losses.

Mycoplasma infections are caused by contagious bacteria passed between sheep through close contact, respiratory secretions, milk, and contaminated milking equipment or hands. In lactating flocks, infected milk is especially important. Merck notes that chronically infected animals may continue shedding organisms, which helps explain why some problems keep returning even after a few sheep seem to recover.

Different species tend to cause different patterns. Mycoplasma agalactiae is the main cause of contagious agalactia in sheep and goats, with mastitis, arthritis, and conjunctivitis as hallmark signs. Mycoplasma ovipneumoniae is commonly linked to respiratory disease and can weaken airway defenses, making secondary infections with organisms such as Mannheimia haemolytica or Pasteurella multocida more likely.

Stress often makes outbreaks worse. Recent transport, crowding, poor ventilation, weather swings, lambing pressure, nutritional strain, and mixing new animals into the flock can all increase risk. Lambs, milk-producing ewes, and animals with other respiratory or udder problems may be affected more severely.

Not every exposed sheep becomes obviously sick. Some become subclinical carriers, which is one reason flock history, quarantine practices, and testing of suspicious milk or respiratory cases are so important.

Diagnosis starts with a flock history and physical exam. Your vet will look at the pattern of disease: coughing lambs, ewes with abnormal milk, multiple lame sheep, recent additions to the flock, and whether signs are clustered after lambing or periods of stress. Because mycoplasma signs overlap with other causes of pneumonia, mastitis, and arthritis, exam findings alone are usually not enough.

Laboratory testing is the key step. Merck states that diagnosis of contagious agalactia depends on PCR, culture, or both, and serology may help in unvaccinated herds. Depending on the case, your vet may collect milk samples, nasal swabs, deep respiratory samples, joint fluid, or tissues from necropsy. Cornell’s diagnostic guidance for mycoplasmal mastitis also emphasizes organism detection from milk because animals may shed mycoplasma even when signs are not dramatic.

Additional tests may include milk cytology or culture, CBC and chemistry, ultrasound of the udder, joint taps, or necropsy of animals that die. In respiratory outbreaks, your vet may also test for secondary bacteria and other flock diseases. That broader workup helps build a treatment plan that fits the situation instead of assuming one organism is the whole problem.

For budgeting, many US diagnostic labs list mycoplasma culture or PCR in roughly the $30-$135 lab fee range per sample, before veterinary collection, shipping, and interpretation. Total on-farm diagnostic costs are often higher once the farm call and sample handling are included.

Prevention focuses on biosecurity, early detection, and reducing spread within the flock. Quarantine new arrivals before mixing them with the main group, and ask your vet whether testing is appropriate for animals coming from flocks with respiratory disease, mastitis, or chronic lameness. Avoid sharing equipment between groups unless it is cleaned and disinfected. In dairy or hand-milked settings, careful udder hygiene and milking order matter, especially if any ewe has abnormal milk.

Good housing also helps. Reduce crowding, improve ventilation, keep bedding dry, and lower stress around transport, lambing, and weaning. Because Mycoplasma ovipneumoniae can contribute to respiratory disease and set sheep up for secondary bacterial pneumonia, managing air quality and limiting nose-to-nose contact between sick and healthy groups can make a real difference.

For mastitis-prone flocks, monitor milk quality, udder texture, and lamb growth closely after lambing. Ewes with repeated abnormal milk, udder atrophy, or poor nursing performance should be discussed with your vet. Chronic shedders can keep infection circulating even when only a few animals look sick.

Vaccination may be discussed in some regions or production systems, but Merck notes that vaccine efficacy for contagious agalactia varies and vaccination during an active outbreak is not recommended. That means prevention usually depends more on flock management, testing, and practical culling decisions than on a vaccine alone.