Conductivity measurement
Methods of determination
Conductivity (or Electrolytic Conductivity) is defined as the ability of a substance to conduct electrical current. It is the reciprocal of the resistance.
In a healthy animal*, the mean value of electric conductivity is:

Milk type

Conductivity values

Cow milk

between 4 to 6 mS/cm (18C);

Sheep milk

between 3 to 5 mS/cm (18C);

Buffalo

between 2,5 to 5 mS/cm (18C);

* These values depend on the geographical region, the breed and on other factors.
  • Milk conductivity changes on the concentration of ions in the milk:
  • Added water, sugar, proteins, insoluble solids

    Decrease the ion's concentration. Milk conductivity decreases.

    Added salts

    Increase the ion's concentration. Milk conductivity increases.

    Significantly extreme value (6,5 - 13,00 mS/cm (18C)

    Should indicate the development of mastitis. Infections damage the tissue of the udder. This allows sodium and chlorine ions from the blood to be released into the milk. The concentration of ions in the milk is thereby raised, and it can more easily conduct an electrical current - the conductivity of the milk increases.

  • Milk conductivity can be used as tests for degree of water evaporation in condense milk production.
  • Milk conductivity change notifies of powder (dry) milk solution rate.

  • Mastitis:
    Mastitis results in changes in the electrical conductivity of milk, primarily because of changes in the concentration of sodium, potassium and chloride ions. Measurement of conductivity can therefore assist in the early identification of mastitis.
    Mastitis is an inflammation of the mammary gland and is usually caused by bacteria infection of the udder tissues.
    Mastitis is the most costly disease on the dairy farm today. According the statistical information total losses for the United States are in the range of 1.5 to 3 billion USD annually, or 11% of the total USA milk production.
    Mastitis can be clinical or sub-clinical. Clinical mastitis gives abnormal milk and swelling of the udder. Bacteria are present in the milk, and the composition of the milk is dramatically changed.
    Sub-clinical mastitis is more problematic because no visible changes appear in the milk or the udder, but milk production decreases, bacteria are in the milk, and the composition is altered. Mastitis, has a very negative effect on product quality, due to increased enzymatic activity, coming from both proteolytic and lipolytic enzymes. This effect will reduce cheese yield, butter yield, change acid production in fermented products and lead to taste defects in all kinds of dairy products.
    To encourage farmers to lower the level of mastitis, many dairies offer premium payment programs for milk free of mastitis and reduction in payment for milk with high mastitis level.
    Dairy Herd Improvement (DHI) supports the farmers by monthly milk recording and testing or mastitis on individual cows.
    The relationship between milk electrical conductivity and udder health resulted in adding this milk conductivity meter as an option to our milk analyzer. There is a strong relation between the electrical conductivity of the foremilk and its lactose and salt content. Illness not related to the udder, problems in metabolism, changes in the diet, breed, stress and the stage of lactation influence the conductivity whilst having a lesser influence on somatic cell count. Conductivity readings are not a measure of somatic cell count. Both are associated with the presence of infection but only a general correlation exists between them. Studies of milk electrical properties and mastitis indicate there is no fixed point or number where mastitis is definitely present, or not present. Rather, there are increasing or decreasing degrees of infection as conductivity changes.
    Using the Lactoscan and measured conductivity in significantly extreme value (6,5 - 13,00 mS/cm (18C) is an indication of mastitis development. The farmer can use the results to fight sub-clinical mastitis and by that optimize milk production both concerning the amount and the quality of the milk.
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