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Mastitis

Mastitis

Mastitis in dairy cows.
Mastitis is the costliest disease of dairy cattle and each year causes economic losses of 35 billion dollars in the global dairy industry, which represents a 7-8% shortfall in dairy revenue.

Bacteria are normally classified into 3 groups: environmental, contagious and mix infections.

  • Contagious organisms are well adapted to survival and growth in the mammary gland and are frequently responsible for chronic infections. Examples are Staphylococcus aureus, Streptococcus agalactiae and Mycoplasma spp.
  • Environmental organism: They live in the environment, mainly in the bedding, and the infection happens between milkings. They produce short duration intramammary infections and they have high clinical incidence.. Examples are Escherichia coli, Streptococcus uberis and other coliforms like Klebsiella spp.
  • Pathogens with mixed characteristics like Coagulase Negative Staphylococci (CNS) and Streptococcus dysgalactiae.

SIGNS

Mastitis is an inflammation of the udder which can be defined as either clinical or sub-clinical:

  • Clinical mastitis: Detection of clinical mastitis is based on 3 parameters. Depending on how many are affected, we will have a different grade of mastitis. The classification is as follows:
Mild Milk secretion altered GRADE 1
Moderate Milk secretion and mammary gland altered GRADE 2
Severe Secretion, mammary gland and general state of health altered GRADE 3

Diagnostic Methods for Investigating Mastitis and Udder Health Problems

Diagnosis of clinical mastitis is based on the appearance of abnormally appearing milk. Milk may be off color, watery, bloody or have the appearance of serum. Abnormal milk may also contain varying amounts of puss and clots. The amount of swelling, severity of pain and the overall appearance of the cow will indicate the severity of infection and serve as a guide for the course of treatment.

Milk culture of suspected quarters or cows (composite samples) will identify the presence of mastitis pathogens but will not provide a measure of the degree of inflammation associated with the infection. Individual cow SCC will provide a determination of the level of infection within the herd.

VETALB -Laboratory Tests

Milk Cultures

Culturing milk from the bulk tank, individual quarter or cow, groups or categories of cows adds an additional dimension to evaluating udder health and mastitis control programs especially when that information is combined with SCC or clinical mastitis data. Routine milk cultures should be an ongoing part of any mastitis control program. The sampling strategies for any ongoing program require the input of the herd veterinarian as well as herd management. It is particularly important that milkers be aware of any standard procedures for identifying cows to sample as well as appropriate sampling procedures.

Individual Cow Samples

Cultures alone provide an indication of the possible pathogen involved. However the possibility of a false positive result due to contamination of the sample with organisms present in the teat canal, teat skin or environmental contamination of the sample will affect test specificity. Infected animal not currently shedding pathogens may have a negative culture result hereby affecting test sensitivity. Test sensitivity and specificity are about 70% for single cultures. When multiple samples of the same animal are take sensitivity remains about the same however test specificity increases to 80 – 90 %.

Bulk Milk Cultures

Sampling the bulk tank milk (BTC) is a simple, inexpensive means of determining the presence of mastitis pathogens in a herd. This culturing method does have its limitations and is best suited for the identification of contagious mastitis pathogens and for monitoring the presence of pathogens over time.

Individual Cow Somatic Cell Counts (SCC)

Individual Cow SCC determination is most commonly performed on composite samples (comingled milk from all 4 quarters) and gives results in 1,000s cells/ml. Ideally, this should be done every month. It is an indicator of how the cow is reacting to the infection. We consider as healthy, cows under 200,000 cells/ml. Cows above this threshold without clinical symptoms are considered sub clinically infected. In heifers, we normally use 100,000 cells/ml instead of 200,000 cells/ml as threshold. The SCC is mainly altered by intramammary infections (IMI) but variation can be the result of other factors (age, season, other diseases, etc.).

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