Milk samples may be collected individually from each affected quarter (quarter milk samples) or combined from multiple quarters of a cow into one sample tube (composite milk samples). Composite milk samples are not recommended however, as cultures usually reveal growth of numerous different bacterial species, making it difficult, if not impossible, to determine which pathogens are causing mastitis and which are environmental contaminants. Isolation of contagious organisms, such as Staphylococcus aureus, Streptococcus agalactiae, or Mycoplasma sp., are indicators of true infections of the udder. Environmental organisms, such as Streptococcus spp., coliforms, Staphylococcus spp., (coagulase negative Staph.), Pseudomonas sp., Corynebacterium sp., yeast, and fungi, may be contaminants or true infections. Unless only screening for contagious pathogens, composite milk samples should be avoided.
Milk samples may become contaminated with bacteria from the hands of the sample collector, the environment, and the teat, skin or teat canal of the cow. It is important that proper sample collection techniques are used in order to avoid contamination of the milk sample.
Milk Sample Collection Guidelines
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