With some milk buyers and processors dropping the threshold of an acceptable bactoscan, producers’ attention must be turned to ensuring all aspects of milk production are of a high standard to ensure that penalties are not being received for a high bacterial count.
In addition, and probably just as important is that high milk bactoscan results will be a good indicator of other underlying herd management issues.
Bacterial contamination is the most important cause of hygiene-related problems as milk is a superb source of food for bacteria.
When milk is at a temperature of 35°C bacterial numbers can double within half an hour – therefore within two hours 1,000 bacteria per ml of milk can become 10,000 bacteria and, within 5 hours, 1,000,000.
Temperature is key, below 5°C the bacteria which affect milk quality do not multiply. The bacteria are not killed but are dormant, waiting for an increase in temperature to start reproducing again. High levels of bacteria in milk affect both its manufacturing properties and its shelf life. (Laven, 2016).
Bactoscan in the UK
Bactoscan is now the standard method in the UK for the determination of milk hygienic quality in the UK.
The method involves centrifuging the milk to separate the bacteria and other heavier particles from the main body of the milk, the bacteria is then stained and counted. The process takes less than 7 minutes – a huge improvement over the turn-around time required for the old culture method and, unlike culture, it can be completely automated.
The bactoscan measures the actual number of individual bacteria whereas culture measures the number of colonies which grow in the laboratory. Culture is therefore affected by the natural tendency of bacteria to clump together in milk, reducing the number of colonies which form.
Bulk Tank Analysis – Bactoscan
A more in depth analysis of the bacterial populations contributing to the bulk tank bactoscan can give an indication of the source of the problem and are also useful in identifying the bacteria responsible for mastitis within an individual herd.
This is referred to as the bulk tank analysis.
The presence of thermoduric bacteria are associated with inadequate sanitisation of the plant. These bacteria are able to withstand high temperatures.
Coliform analysis which include faecal streps and e.coli are used as indicators of the presence of other organisms of faecal origin including yeasts and fungi and are associated with environmental contamination. Environmental contamination arises mainly from faecal contamination and is an indicator of poor hygiene. Poor teat preparation prior to milking can give rise to high coliform counts.
Unlike the coliforms the pseudomonas are non-enteric in origin, that is, not arising from the gut of the cow, but like the coliforms are an indicator of environmental contamination. These micro-organisms can survive and multiply at low temperatures and are classed as psycotrophs.
Total Staph Count
Despite its name the Total Staph Count includes both the environmental pathogen Strep Uberis as well as all the Staphs including Staph Aureus – an important cause of contagious mastitis. Strep Uberis is largely associated with straw bedding and is a common cause of both clinical and sub-clinical mastitis.
Differential bacteria screening goes beyond the bulk tank analysis outlined above and drills down into the specific type of bacteria present in the milk. Again this can be a very useful tool for investigating causes of mastitis on a herd level.
The presence of Strep dysgalactiae for example can suggest problems with teat condition or damage, whereas the presence of corynbacterium bovis can suggest problems with post milking teat disinfection. It is worth remembering that strep agalactiae will be the main cause of high cell counts.
With the increased prevalence of mycoplasma in the UK it may well be worth screening for it in the future. Mycoplasma are very different to other types of bacteria in that they lack a cell wall around their cell membrane. This means that they do not respond to treatments based on penicillin or Beta Lactams that are designed to disrupt the production of cell wall components.
What can be done as a producer to reduce bactoscan results and improve hygiene within the milk sample? Bacteria are everywhere in the air, water and even on skin. The challenge is stopping the normal level of bacteria from becoming a problem.
Bactoscan failures arise from one of four main causes:
- Contaminated Plant: if the plant is not being sufficiently cleaned, then bacteria will survive between milking’s and begin to contaminate milk from the next milking. ‘Just 5ml of milk residue (teaspoon) can contain sufficient bacteria to cause a failure on thousands of litres of milk’ (Laven, 2016). This is the most common cause of bactoscan failures.
- Mastitis: Mastitis, especially environmental pathogens is the second most common cause of bactoscan failure. The presence of Strep Uberis pathogens, even at a sub clinical level can cause cows to excrete large numbers of bacteria, resulting in high bactoscan results.
- Refrigeration Failure: if milk fails to cool quickly to below 7˚c, it can cause bacteria within milk to multiply causing high bacterial counts.
- Environmental Bacteria: Bacteria from mud, manure, feed and other sources can contaminate the teats. If teat preparation is not effective, the risk of contamination during milking when the cluster is put on is very high.
After a high bactoscan a thorough check of the plant must be undertaken to ensure that everything is working correctly, everything from split liners to remaining milk residues can cause problems.
Richard Laven PhD BVetMed MRCVS has put together a 4 point action plan for responding to Bactoscans.
1) Plant cleanliness:
a) Make sure that the cold water rinse after milking removes the majority of milk residues
b) The plant should be cleaned and disinfected after every milking and the tank should be rinsed and cleaned after every collection. The milk filter should be inspected and changed after every milking.
c) Ensure air lines are free from dust and milk-split liners area common cause of milk in air lines.
d) Regular inspection of the plant is essential to ensure there is no build-up of milk residues.
e) Check rubber wear regularly and replace it if it is cracked or perished.
2) Cow preparation and health
a) Have a consistent routine of teat preparation prior to milking. Clean soiled teats with a dry wipe if possible. Avoid over-wetting the udder. Pre-milking teat dipping of cleaned teats can significantly reduce bactoscans.
b) Check that the water used in the plant is not contaminated.
c) If subclinical mastitis is the problem, get a herd test done to identify the infected cattle. Then stop milking these cows into the tank and treat them with antibiotics.
3) Milking routine
a) Wear rubber gloves and disinfect them regularly during milking.
b) Ensure clusters which fall or are kicked off during milking are clean before replacing.
4) Milking machine maintenance
a) Check that the temperature of the milk entering the tank is no more than180C, and that of the milk in the tank is below 70C within three hours of milking. This should be done at least 4 times per year
b) Maintain the milking machine in good working order. Testing at least once per year is essential.
Bulk tank analysis is a useful tool for examining and investigating the underlying causes of high SCC, mastitis incidence and milk hygiene problems.
The Wynnstay Animal Health and Dairy technical services team are on hand to discuss the results and to help you implement solutions.