Corynebacterium Bovis

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Corynebacterium Bovis

Also known as

Summer mastitis

Corynebacterium bovis is a pathogenic bacterium that causes mastitis and pyelonephritis (urinary tract infection) in cattle.

Sporadic cases of mastitis caused by C. bovis occur in dairy herds but this bacterium is a common inhabitant of the bovine udder and usually considered to nonpathogenic. It can colonize in the epithelium of the teat canal, however,and cause a small rise in the milk cell count.

Level of infection is very low in herds where teat dipping and dry period treatment are practiced. These bacteria are rarely a cause of udder disease but often found in random milk samples.

Corynebacterium bovis is highly infectious but also very responsive to teat disinfection, and can therefore be an indicator of teat-dipping efficiency and efficacy in a dairy herd.


  • Elevated somatic cell count in milk
  • Mild inflammation in the udder


Corynebacterium bovis can cause “summer mastitis” indairy heifers, and mild mastitis in dry cows and beef breeds

This bacterium is an anaerobic, Gram-positive organism. When viewed under a microscope it is characterized by straight or curved rods that are slightly larger on one end. When cultured, they form branching aggregations that look like "Chinese characters".

In mastitis infections, C. bovis is spread from cow to cow most commonly through improper milking technique but is usually just a mild infection resulting in an elevated somatic cell count.

Milk taken aseptically from a healthy cow may contain no micro-organisms, or very low numbers. The most frequently isolated organisms are micrococci, streptococci, and Corynebacterium bovis.

Higher microbial counts are often seen if the animals suffer from mastitis, and under those circumstances, many types of bacteria are seen, including some that are much more pathogenic.

Corynebacterium bovis colonizes the teat canal and produces small, white, powdery or granular colonies after 48 hours.  


Proper milking procedures including the use of effective post-milking teat disinfectants can reduce the number of new infections. After detaching the milking unit, application of a proven post-milking teat disinfectant should cover at least two-thirds of the teat.

Post-dips containing the active ingredient linear dodecyl-benzene sulfonic acid are not effective against C. bovis. Proper dry cow therapy is very effective in eliminating this pathogen. Prevalence is very low in herds utilizing an efficacious post-dip.


This bacterium is sensitive to most antibiotics, including the penicillins, ampicillin, cephalosporins, quinolones, chloramphenicol, tetracyclines, cefuroxime, and trimethoprim.

There is some controversy, however, regarding attempts to completely eradicate (versus simply limit) C. bovis infection in the udder. This particular bacterium along with several other organisms seem to be normal inhabitants of a healthy udder.

There is some thought that subclinical mastitis (and continuous low level of white blood cells in the milk) acts as a protection against more serious infections.

Control programs that reduce cell counts to very low levels in milk may reduce the udder’s resistance.  The mildly pathogenic bacteria like C. bovis may be important in maintaining disease resistance in the udder.

Studies have found that infection rates with pathogenic bacteria is significantly lower in quarters that harbor C. bovis than the quarters that do not. An intensive program to disinfect udders/teats could eliminate C. bovis and increase susceptibility to other pathogens.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.