By: Ronald K. Tessman, DVM, Ph.D., DACVIM, DACVPM, Beef Cattle Technical Consultant, Elanco Animal Health
GREENFIELD, Ind. (Nov. 29, 2023) – Mycoplasma bovis (M. bovis) is a small, pleomorphic bacterium in cattle that commonly affects feedlot cattle. Like other pathogens infecting cattle, M. bovis can have significant implications on cattle productivity and operational profitability. M. bovis is especially concerning for producers because the bacteria do not have a cell wall, meaning it has a poor response to some commonly used antibiotic therapies.
It can be very difficult to identify when feedlot cattle are infected with M. bovis because the bacteria do not immediately trigger an immune response, meaning clinical signs of disease can take a while to appear. The opportunistic nature of the bacteria allows it to grow slowly or even lay dormant until the host’s defense mechanisms are compromised, taking the first opportunity to attack the animal’s suppressed immune system.
Stress from weaning, transportation and nutritional transition, coupled with M. bovis’ ability to inhibit an immune reaction to fight off infection can lead to a variety of serious, sometimes life-threatening diseases, including:
- Chronic pneumonia
- Myocarditis: A condition that causes inflammation of the heart muscle
- Tenosynovitis: A disease that infects the joints and surrounding tendons causing severe inflammation
- Otitis: An infection of the middle ear caused by severe swelling
- Conjunctivitis: An infection of the transparent membrane that lines the eyelid and eyeball, also known as pink eye
Although M. bovis is most associated with these chronic diseases, more recently, M. bovis has been increasingly identified with Mannheimia haemolytica, Pasteurella multocida and Histophilus somni, common pathogens in the BRD complex, leading to serious and often chronic respiratory disease. More concerning, M. bovis can also induce significant respiratory disease in the absence of these primary BRD pathogens.
Pathological changes
Pure mycoplasma cultures confirm that animals experiencing respiratory disease caused by M. bovis will have gross lesions that are often discolored and fibrous.1 Lungs are firm on palpation and small BB-like abscesses that have combined into a larger mass may be present on one or all lung lobes. Additionally, there will be lobular or lobar consolidation, meaning normally air-filled sacs of the lung are instead filled with bacteria and inflammatory materials. It can be highly variable and often doesn’t correlate with clinical disease severity. Severely ill calves may have little to no lung consolidation.2
Transmission
Mycoplasma organisms require special media and growth conditions.3 M. bovis is usually transmitted by direct contact with an infected animal. The pathogen will multiply with no clinical signs and then wait to attack when the host’s immune function is suppressed.
Once a calf sheds the pathogen, it can shed for months. However, it is not clear if it is a persistent infection or if it is a repeated clearing and reinfection. M. bovis appears to move quickly among cattle by respiratory route when introduced to a naïve group of cattle, leading to a high prevalence of M. bovis among newly received feedlot cattle.
Clinical signs
Cattle infected with M. bovis can show clinical signs including nasal discharge, cough, often appear depressed and may have excessive tearing. Rectal temperatures are often elevated but may be lower than what is associated with other BRD pathogens. In herd outbreaks it is not uncommon for a percentage of animals to present with lameness associated with infectious arthritis or tenosynovitis. They may also have dropping ears with or without a head tilt due to otitis, a middle ear infection.4
Diagnosis
Definitive diagnosis of M. bovis associated BRD may be difficult. Several mycoplasmas can be cultured from cattle that have been associated with sporadic disease. That’s why most recent recommendations have focused on PCR diagnosis. The sensitivity and specificity of these methods are reportedly high.3 However, we must be careful when using these tests because, most often, the reported sensitivities and specificities are analytical rather than clinical.5 In most practical cases, diagnosis can be made based on clinical signs, pathological changes and history.
Treatment and control
Since M. bovis is difficult to diagnose, can cause multiple chronic infections and responds poorly to antimicrobials, it can be challenging to treat and control. Antibiotics with label indications for M. bovis including florfenicol, enrofloxacin and tulathromycin can be effective tools in treating infections caused by the pathogen when the proper dose is administered at the onset of clinical signs. When using antibiotics, practicing antibiotic stewardship is key. Determining an accurate dosage by weighing calves can help to both ensure efficacy and reduce risk of overuse of antibiotics. Regardless of the antibiotic used, producers should continue to closely monitor calves and follow recommended protocol for re-treatment.
Like other bacterial infections, proactive management practices and prevention are instrumental for reducing the occurrence and impact of M. bovis in feedlot cattle. Vaccinating calves can help build immunity to viruses that predispose to bacterial infection. Taking steps to minimize stress in transport, upon arrival and throughout transition can play a vital role in supporting the immune system so its defense mechanisms can focus on warding off infection. Producers may also consider categorizing cattle by risk level for disease upon arrival to allow for consistent monitoring and support to mitigate a disease outbreak.
M. bovis is an elusive pathogen. That’s why prevention tactics, proper diagnosis and antibiotic therapy are key for reducing the transmission, colonization and attack of this pathogen and its impact on cattle health and a producer’s bottom line.
To learn more about tools to help prevent, treat and control M. bovis on your operation, talk with your Elanco representative today or visit ElancoBRD.com.
