Bactoscan

Introduction

The Bactoscan is a measurement of the number of bacteria present in milk (usually expressed as e.g. 20, meaning 20,000 bacteria/ml). High bacteria levels reduces the shelf life of liquid milk and may affect the ability to produce good quality cheese. There are also legal requirements set by the EU in order for the milk to be suitable for human consumption, currently set at a maximum of 100,000 bacteria/ml. Other targets are set by the milk buyer with financial penalties for producers that go over the predetermined level set out in their contract. This is to incentivise farmers to be as hygienic as possible and give the manufacturer an acceptable product to pass on to the consumer. However, a low Bactoscan is also desirable as it can reflect good parlour management, a clean environment and a low level of mastitis in the herd.

Reasons for a High Bactoscan

1. Poor teat hygiene
   Due to contamination of the teats from the environment entering the milk.
2. Poor milk refrigeration
   Allowing the overgrowth of low levels of bacteria that are found in all milk prior to processing.
3. Poor parlour washing
   If the parlour is not washed properly after milking, there can be a build up of residues that encourage bacterial colonisation that can elevate the levels of bacteria in the milk.
4. Mastitis (clinical or subclinical)
   Infection of the mammary gland will usually cause elevated bacterial counts from affected cows. Certain types of infection tend to cause particularly high levels such as S. uberis and S. agalactiae.

Investigation of a high Bactoscan level on a dairy herd

When investigating a herd with a high Bactoscan problem, the following areas should form the basis of the investigation.

1. Record analysis
   All types of mastitis investigation must begin with an analysis of any available records. For Bactoscan investigations, patterns may be seen when high levels tend to occur with levels usually reported weekly from the dairy to the farmer and may be available online. If the Bactoscan has large fluctuations, this may be consistent with a mastitis problem with peeks occurring due to flares up of subclinical infections or clinical cases not being detected and entering the bulk milk tank. Seasonal trends may suggest an environmental problem. Alternatively a relatively recent but very large and sustained increase should ring alarm bells that there is a problem with the cooling system necessitating immediate action. Failure in the wash up routine may create a similar pattern or may be a slower increase depending on the specific problem.
   
   
2. Environment
   If cow cleanliness is poor, then this can be a reason for raised bulk milk Bactoscan level. Methods to objectify the level of cleanliness have been described and form the basis of a useful tool to use on farm. This tends to be a problem seen during the housing period, but not always and farms practicing seasonal pre-milking teat disinfection may be caught out by poor weather or a badly poached field.
   
   
3. Parlour routine
   Monitoring procedures in the parlour is essential as part of any Bactoscan investigation. Occasionally, very dirty cows may have their udders and teats washed and clusters applied before being wiped dry. This effectively creates a suspension of bacteria on the teat that can actually make the Bactoscan worse! A herd's pre-milking teat disinfecting protocol should also be assessed. Possible problems include the disinfectant not being left on long enough (usually there is a 30 second recommended contact time), the teat not being effectively wiped dry or ineffective products being used. Some farms may only use disinfection during the housing period when teat contamination risk is highest, which can still be effective for controlling the Bactoscan. The extent of gross contamination in milk can be visibly assessed by looking at the milk sock after milking.
   
   
4. Wash up routine
   The wash up routine should be investigated. Using cold water for the first rinse can congeal butterfat within the pipes which favours bacterial colonisation and growth and thus may raise the Bactoscan. For circulation washing, which is the common method used in the UK, the temperature of the water at the end of the wash cycle should not fall below 40°C which can be associated with the same problem. This can be measured with a thermometer as the water leaves the system as part of the investigation. Adequate boiler capacity is needed to supply sufficient hot water for the cycle which should also be checked. When the hot wash is occurring it should not be possible to hold onto the stainless steel pipes in the parlour. If this is possible, it indicates too cool a water temperature.
   
   
5. Bulk Milk Bacteriology
   Bulk milk bacteriology can be a very useful tool for Bactoscan investigations for distinguishing the causes. However, its limitations must be considered and it should not be a substitute for a more thorough investigation.