Consequences of definitions of acceptable milk quality for the practical use of automatic milking systems

The general conditions of hygiene in milk production in the EU are defined by the Commission Directive 89/362/EEC (1989) but not all elements apply to automatic milking. The following text is proposed to be included in the coming EU Hygiene Directive:

Milking must be carried out hygienically ensuring in particular: - that milk from an animal is checked for abnormalities by the milker or a method achieving similar results and that only normal milk is used for human consumption and that abnormal, contaminated, and undesirable milk is excluded.

This text is based on the following definitions of normal, abnormal, contaminated, and undesirable milk:

• Normal milk: Milk suitable for human consumption.
• Abnormal milk: Milk which differs from normal milk in respect of colour or homogeneity.
• Contaminated milk: Milk which, prior to the milking of the animal, is known to be unfit for human consumption following treatment of the animal with antibiotics or other veterinary products which have a requirement that the milk must be withheld from sale for such use.
• Undesirable milk: Milk which, prior to the milking of the animal, is known to be unsuitable for human consumption, e.g. colostrum, high somatic cell count.

The definition of abnormal milk caused by clinical mastitis is proposed to be based on the homogeneity of the milk and not on the colour since the colour of the milk changes with breed, stage of lactation, feed stuff etc. The reference method is suggested as filtration of the milk through a filter with a pore size of 0.1 mm and milk where clots are clearly visible in such a filter is then defined as being abnormal. Incidences of watery and yellowish milk may or may not be detected by this method. Requirements of sensitivity and specificity have not been determined yet but should be equal for all milking systems. It is recommended that the specificity should be >99% to be well accepted by farmers. A sensitivity of 80% may apply. The frequency of visible blood in the milk is rare but regarded as abnormal. Secretion from the udder in the first 3 days after calving is mainly colostrum, which is not regarded as “normal” milk. A high cell count is a clear indicator of inflammation in the udder but cannot be required to be measured at every milking for determination of abnormal milk.

A workshop was held on 27th November 2002 on definition of normal and abnormal milk at time of milking. The main purpose of the workshop was to present background material for a definition, discuss the intention and consequences of the definition, and finally outline agreements and disagreements. There was consensus at the workshop that:

• There should be no double standards.
• If clots appear, the milk is abnormal.
• Milk that has changed in colour because of the level of red blood cells present is regarded as abnormal milk.
• The cell count should not be included in the definition of abnormal milk.

The workshop was not convinced about the reference method for detecting abnormal milk and had question marks on the reference for blood in milk. The colostral period was stated as at least 72 hours with no further requirements. Sensitivities and specificities of reference methods were not established.

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