Milk Quality Flashcards
What is the role of the farm vet in VPH dairy farms? (4)
- Promote and ensure cow cleanliness (environment). Promote Ahw
- Review and monitor milking routines (how it is harvested)
- Monitor and investigate Bactoscan/TBC (monitor the lab data, collected for you and emailed to you)
- Investigate antibiotic failures/review testing systems (Occasionally the AB may get in the milk and all the milk goes in the drain)
What happens to all bulk milk collections?
ALL bulk milk collections routinely tested for antibiotic residues (EVERY single milk batch) – mostly Abs but other tests too.
e.g. Inhibitor detection
Delvotest (Industry standard); broad range of inhibitors detected
e.g. Immunological based tests
Narrow range, detect specific molecules
Betastar, Charm, IDEXX Snap
V. Sensitive to penicillin. Some of the farms have tests on farm before putting in the bulk.
How can we assess the milk quality? (2) What is the difference between these?
TBC/TVC measures live bacteria and is a count of colonies growing on a plate
Bactoscan counts both viable and non-viable bacteria as well as those that would not grow when using the TBC method.
Bactoscan is automated – live and dead bacteria and will always give a higher count than the TBC. Often get a higher reading with bactscan! – can be confusing.
INDIVIDUAL BACTERIA
Farmers are penalised for high Bactoscan counts!
What are the sources of bacterina in milk? (4)
- from the udder of infected cows
- Streptococcus spp. infections
- e.g. S. agalactiae (most common) – shed in vast numbes. caused ‘spikes’ in TBC
- 100,000,000 organisms/ml in mastitic milk
- 2,000,000,000,000 in 2 litres from a mastitic quarter
- Would elevate TBC from 5,000 cfu/ml to 205,000 cfu/ml in a tank of 1,000 litres….
- from the environment
- Especially faecal organisms
- But also water and bedding
- from the milking machine
- Poor wash up routine
- Circulation cleaning
- Temperature of the wash water
- ..and cleaning the bulk tank itself
- MUST BE CLEANED INTERNALLY!
- failure of refrigeration
- Thermoduric psychrotrophs will flourish
What are the 4 obvious things to consider when there are bactoscan problems?
Cow cleanliness
Teat preparation
Milking machine wash up (strip down plant, bulk tank)
Mastitis detection!
What do we do if the 4 obvious causes of bactoscan problems have been ruled out?
Bulk Tank Bacteriology (need a sample)
Needs to arrive at the lab chilled
Can give indication of likely source of problem
Needs to be done by specialist lab
Easy to misinterpret!
Often over-interpreted
Is not as straightforward as many suggest!
What is qualitative bulk tank bacteriology?
Qualitative’
i.e. WHAT bacteria are present
As a lead in to SCC / Mastitis problem
Care in interpretation - do findings reflect udder?
What do they tell you about the herd situation?
May reflect just one cow!
Sensitivity and Specificity
Take care – if you find E.Coli is it from the cow or milker or tank?
Staph – may not mean a herd problem could just be from ¼ of a cow yesterday!
What is quantitative bulk tank bacteriology?
‘Quantitative’
i.e. HOW MANY organisms are present and different temp
For use in Bactoscan investigations
What are the 6 different selections for qualitative bulk tank bacteriology? What does it test for?
Blood agar (allows growth of most organisms)
MacConkey agar (coliform selective)
Edwards agar (Streptococcus spp. selective)
Sabouraud agar (Yeast and mould selective)
Baird Parker (Staphylococcus selective but not a good selection)
Mueller Hinton agar (sensitivity testing)
What is the methodology of quantitative buld tank bacteriology?
Milk Agar (TBC/TVC, Thermoduric count
and Psychrotrophic count
VRB Agar (Violet Red Bile) for Coliform count
Pipettes, Universals, Plate counter
Prepare dilutions (e.g. 10-1, 10-2, 10-3)
Add 1ml of diluted milk to 12-15ml of appropriate agar (at <50oC) and pour
Incubate
TVC, Coliforms, Thermodurics (48h @ 37C)
Psychrotrophs (6 days @ 2-8C)
Perform counts
Take mean of two plates
Aim to count at dilution with gives 30-300 colonies per plate (need to be able to see the colonies on the plate)
>10% variation repeat process
Calculate cfu/mL by adjusting for dilution
What does contamination from the udder of infected cows cause in the milk?
Spikes
Streptococcus spp.
Others more difficult to interpret
What contamination is seen in milk from the environment?
Coliforms
(mostly Enterobacteriacae)
Psychrotrophic organisms
(grow at low temperatures) e.g. listeria or pseudomonas
What bacterial contamination is seen from the milking machine?
Thermoduric bacteria
(temperature resistant) – bacteria which are growing at higher temperatures. Washing routine must be inadequate.
What bacterial growth is seen in milk from the failure of refrigeration?
Psychrotrophic organisms
(grow at low temperatures)
What is the effect on sand vs RMS bedding on mastitis?
RMS – recovering fibre from manure and drying. Recycled manure solids. Very high TBC. However, doesn’t come back as necessarily having high bacteria in milk! Much lower in milk.
Average bacteria in sand is around 2billion. Higher bacteria in the milk tho
