Mycoplasma Mastitis: Control and Eradication in Dairy Herds

Bovine mastitis due to Mycoplasma species is a problematic cause of sub-clinical disease in dairy herds worldwide. Commonly symptomless, it reduces milk yields and quality, spreads easily through the milking herd, and seriously compromises herd profitability. Control requires definitive and regular testing, then culling affected animals or segregating and milking them after the main herd. Furthermore, since it difficult to spot routinely, it is easy to import Mycoplasma infection into a closed herd without rigorous screening procedures, both for live cow replacements and semen for artificial insemination. Most cases of Mycoplasma-induced mastitis are due to infection with Mycoplasma bovis. Initial infection causes a severe reaction in the udder but recovery is frequently associated with reduced yield and carrier status where cows shed the organism intermittently in their milk. It is also worth noting that M. bovis is a potential pathogen in humans, as zoonotic tuberculosis through consumption of raw or unpasteurized milk products¹. Although milk from sub-clinical cases of Mycoplasma mastitis carry higher somatic cell counts (SCC) as an indicator of non-specific udder inflammation, this is not a recognized diagnostic or screening parameter applicable for routine testing. In addition, detection of M. bovis by microbiological culture is complicated; it grows slowly and is difficult to establish from samples that have been preserved or prepared for shipping. One promising area for Dairy Herd Improvement (DHI) sampling is in the use of specific polymerase chain reaction (PCR) assay for M. bovis and other mastitis pathogens. These tests are both rapid (approximately four hours for Thermo Scientific’s PathoProof range of kits) and sensitive, capable of multiplexing reactions to detect a large number of organisms, contagious and environmental, in one assay. A recent white paper investigated the relationship between SCCs and pathogen presence using PathoProof PCR test kits to screen asymptomatic dairy cows in five Dutch herds over three time points². The scientists used the Thermo Scientific PathoProof Major 4.2 Mastitis kit, which detects all major contagious causes of bovine mastitis including M. bovis. This test kit is suitable for raw and preserved milk samples, with results ready within four hours. During initial validation steps, they used a Cq<32 as the cut-off for pathogen detection to determine pathogen presence rather than incidental contamination. Once they detected cases of subclinical mastitis, the team recorded individual SCCs, following the change in counts over the three time points. On analysis, the scientists found that overall cows identified as pathogen-positive by the PathoProof PCR assay had higher SCCs than those identified as pathogen-negative. Applying a diagnostic threshold of >100,000 cells/ml detected only 79% of the subclinical cows identified as pathogen-positive by PCR. Moreover, following SCCs over two time points and using >200% change as an indicator identified only 71% of the pathogen-positive cows as sub-clinical cases. As a rapid screening test, PCR detection seems ideal for initial screening and routine DHI monitoring for subclinical mastitis in dairy herds. Cows identified with contagious pathogens including M. bovis can undergo further specific testing to define the pathogen responsible and the appropriate treatment or herd health management strategy. Through early diagnosis and intervention, dairy herd and public health are improved, and profitability maintained. Read the whitepaper ‘Identification of subclinical mastitis in DHI samples using PCR testing‘ for a full discussion. Resources: 1. Müller, B. et al. (2013) “Zoonotic Mycobacterium bovis–induced Tuberculosis in Humans“, Emerging Infectious Diseases [Internet]. 2013 Jun [date cited]. http://dx.doi.org/10.3201/eid1906.120543 2. “Identification of subclinical mastitis in DHI samples using PCR testing”, Tove Asmussen; Pauliina Heikkinen, Jani Holopainen and Lynne Edhouse http://www.thermoscientific.com/Identification-subclinical-mastitis-DHI-PCR-testing-WP-EN.pdf