In low bulk tank somatic cell count herds, Coagulase-negative staphylococci, as a group, had a larger contribution of somatic cells than any of the other major mastitis pathogens and were important contributors to the total number of somatic cells in bulk milk.
by Linda L. Tikofsky, DVM and Jack van Almelo
Because mastitis caused by Coagulase-negative staphylococci (CNS) is usually characterized by just mild elevations of somatic cell counts (SCC) and less severe clinical mastitis, this group has usually been accepted as a minor pathogen in dairy herd health. However, with improved control of contagious mastitis pathogens such as Streptococcus agalactiae and Staphylococcus aureus, CNS have become the most common mastitis pathogens cultured from udder secretions.
Recent studies have found the number of subclinical mastitis cases caused by CNS to be between 16% and 50%. CNS are the predominant pathogen isolated from pre-calving heifers. Somatic cell counts from quarters infected with CNS usually remain below 500,000 cells/ml. However, increases in SCC over 100,000 cells/ml are associated with reduced milk production. Therefore, herds with a high number of quarters infected with CNS may see an impact in their bulk tank somatic cell counts. If a farm goal is to have an extremely low bulk milk SCC (<100,000 cells/ml) to capture the maximum premiums in their milk check, the increase in bulk milk SCC caused by many cows infected with CNS may have economic consequences.
To better understand the impact CNS may have on production and bulk milk SCC, 15 years of individual cow culture results (352,614) and data (milk production and SCC) from New York state were evaluated. The study found that overall, approximately 9% of all cows in the study were infected with CNS, and when individual herds were evaluated, an average of 15% of cows were infected with CNS. Cows with the lowest individual SCC were associated with no infection; moderate SCC level with CNS and Corynebacterium spp.; and high level SCC with S. agalactiae and S. aureus.
The percentage of the bulk milk somatic cell count (BMSCC) contributed by CNS in herds with BMSCC <200,000 was ~18%; in herds with BMSCC between 200,000 and 400,000 CNS contributed ~12% and in herds with BMSCC greater than 400,000 cell/ml, the percent contribution by CNS was 8%. In low BMSCC herds, CNS, as a group, had a larger contribution of somatic cells than any of the other major mastitis pathogens and were important contributors to the total number of somatic cells in bulk milk.
As with all other types of mastitis, prevention is the key, but management strategies aimed specifically at CNS need additional investigation. Since CNS can be resident microflora on teats and udders, they have long been considered opportunistic pathogens; however, recent studies have shown that certain species are more adapted to the udder environment (S. chromogenes and S. hyicus). Strategies aimed at decreasing bacteria on teats (e.g. dipping) have been shown to reduce CNS populations, as have strategies aimed at improving environmental hygiene. The use of internal and external teat sealants also has been shown to have a preventive effect against new CNS and other intramammary infections in both heifers and cows.
Spontaneous elimination rate of CNS in lactating dairy cattle is high and so treatment may not be indicated for all cases though it should be recommended for quarters with moderate to severe clinical mastitis and/or persistent infection. Selection of antimicrobials should be based on susceptibility testing.
Understanding of CNS mastitis is still quite limited and more research into understanding intramammary infection dynamics, management and cost-effective treatment strategies is encouraged.
QM2 is the newsletter of Dairy One and Quality Milk Production Services.
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Dr. Linda Tikofsky is Senior Extension Veterinarian, Quality Milk Ithaca, Ithaca, N.Y. Contact her via e-mail: email@example.com.
Jack Van Almelo is a member of the Dairy Management Resources Group, DairyOne, in Ithaca, N.Y. Contact him via e-mail: Jack.VanAlmelo@dairyone.com.
QMPS is a program within the Animal Health Diagnostic Center, a partnership between the New York State Department of Agriculture and Markets and the College of Veterinary Medicine at Cornell.
The QMPS staff of veterinarians, technicians and researchers works with New York dairies to improve milk quality by addressing high somatic cell counts, milking equipment and procedures, and milker training in English and Spanish. QMPS also conducts research and teaching programs.
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QMPS website: http://qmps.vet.cornell.edu
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