Milk Quality 1 & 2

Question 1

Milk is a valuable food source, particularly for infants and children, but also in later life (e.g. as a good source of calcium). Bovine milk is predominantly consumed by humans, but milk from other species are also consumed and there are minor differences between species. Milk contains proteins (caseins and whey), lactose (a sugar), minerals and fat. Milk can also contain organisms that are potentially harmful to human health…and pathogens that are particularly important for human health.

Write down the main health hazards that you can think of from milk and dairy products – what potential pathogens could be ingested?

Answer 1

· Campylobacter jejuni, Escherichia coli 0157:H7, ListeriCa monocytogenes, and Salmonella entertica.

· The spoilage of milk products is an enormous economic problem worldwide.

Contamination:

· Faecal contamination from soiled animals, especially teats, udders and tails.

· Bacterial contamination from poor milking practices, soiled hands, soiled equipment and failure to clean and disinfect teats prior to milking.

· Contamination due to failure to detect abnormal milk (mastitis pathogens, blood and clots).

· Physical contamination, especially from perished components in milking machines and bulk tanks, dust, bedding materials, dung, insects and animal hair.

· Bacterial contamination from inadequate cleaning and disinfection of milking equipment and bulk milk tanks.

· Chemical contamination from veterinary product residues, cleaning chemicals and use of non food-grade equipment.

When you have your list, check out the ‘List of Zoonotic Diseases’…there are quite a few! The introduction and ‘milk borne diseases’ section of this paper reminds us that milk can be a dangerous item in the diet, with some infections such as Salmonella spp. and Campylobacter spp. still a problem.

Question 2

Circulation cleaning of the milking plant involves which of the following steps?

Answer 2

Warm rinse, hot wash cycle, alkaline detergent, cold rinse

Question 3

To prevent build-up of milk fat residue, and subsequent increases in bacterial counts in milk, which of the following is important?

Answer 3

Alkaline wash

Question 4

An Acid Boil Wash (ABW) at 96ºC may be periodically used to remove what substance from the interior to the milking plant?

Answer 4

Mineral deposits (‘milk stone’)

Question 5

How many litres of water are required per milking unit for an effective wash cycle?

Answer 5

Between 15 and 20 litres

Question 6

What problems occur with milk tank cleaning? (6)

Answer 6

Problems occur with inadequate temperature, inadequate volume, inadequate chemicals and inadequate circulation, blind ending pipes that are difficult to clean and a failure to manually clean the bulk tank when necessary.

Question 7

What is the temperature at the strat of the hot wash?

Answer 7

Note the start temperature of the hot wash on the boiler photo – this is critical and ensures the wash water will still be 60-70ºC at the end of the wash

Question 8

What are likely to be consequences of not having any form of pre-milking routine?

Answer 8

· Risk antibiotics or other unlicensed in milk products getting into the milk tank

· The farmer is not being able to see the cows prior to milking- this is a good way to check for things like lameness

· Run the risk of increased prevalence of disease e.g. mastitis

· More contamination of the milk e.g. dirt or faeces

· More likely to have milk rejected/may loose money as a loss

The potential consequences of an inadequate or non-existent pre-milking routine may be one or more the following:

· Bi-phasic milk let-down and inefficient milk harvesting – remember the importance of oxytocin release (consider animal husbandry procedures)

· Increased unit on time and development of teat-end hyperkeratosis (consider mastitis)

· Increased risk of environmental mastitis infections

· Increased bacteria in milk (increased ‘Bactoscan’ or ‘Total Bacterial Count’ – see next section)

· Failure to detect clinical mastitis cases – this is very important and if these are missed, will result in mastitis milk entering the supply (increasing the Bactoscan), poor cow welfare (missing disease) and poor chance of cure (delayed antibiotic treatment)

Question 9

What would the sites of contamination suggest regarding likely source? (4)

Answer 9

· Nutrition - Diarrhoea

· Passageways - faeces and urine

· Bedding - mould, faeces, urine

· Ventilation - poor ventilation = condensation = soiling bedding = mould

· Tails and udder - mud, faeces

· Cows with dirty legs indicate faecal splashing from passageways

· Cows with dirty tails indicate loose faeces (link to D14GI Diarrhoea in Adult Cattle lecture) or cubicles that are too small

· Cows with dirty flanks indicate poor lying surface management (e.g. inadequate cubicle bedding, heavily soiled straw yards etc.)

· Cows with dirty udders can be affected by all the sources above. In addition, very poor udder hygiene scores significantly increase the risk of environmental mastitis (see paper and link to mastitis teaching)

Question 10

What would an increased coliform count suggest regarding the likely reason why the Total Bacterial Count/Bactoscan of the milk was increased and the farmer maybe being penalised for unhygienic milk?

Answer 10

An increased coliform count in the bulk milk tank usually suggests inadequate teat preparation prior to milking and poor/non-existent pre-milking teat disinfection, although any part of the milking equipment can become contaminated. Coliforms can originate from other environmental sources as well, including water that is not from the mains supply

Question 11

How many dairy producers (i.e. dairy holdings) are there in the UK currently?

Answer 11

Between 10000 and 15000

Question 12

What is the average dairy herd size in the UK?

Answer 12

Between 100 and 150 cows

Question 13

How many million litres of milk are produced by the UK each year?

Answer 13

More than 10000 million

Question 14

What proportion of the UK milk production is sold as liquid milk?

Answer 14

Around half of it - Although the number of dairy production holdings (i.e. farms) are in decline, there are still around 14,000 in the UK, with a total of 1.9 million dairy cows in the national herd. Average herd size is increasing slowly, and is now approx. 140, with <10% of herds having more than 200 cows. More than 14,000,000,000 litres of milk is produced from the national herd and around half of this is sold as liquid milk – check out the ‘milk flow diagram’ for some details. Each cow produces ~7500 litres of milk per year and on average, each person in the UK drinks 2 litres of milk each week

Question 15

What is ‘High Temperature Short Time’ (HTST) pasteurisation?

Answer 15

HTST pasteurisation was developed from flash pasteurisation and involves heat milk to 71.7ºC for 15 seconds, followed by immediate cooling. This differs from the ‘holding’ method of pasteurisation whereby milk is heated to a lower temperature (around 62 to 66ºC) and ‘held’ there for 30 minutes – this is a common approach if pasteurising colostrum on farm for example.

Question 16

How is the pasteurisation method checked to ensure the correct standard?

Answer 16

The pasteurisation method is checked by testing for alkaline phosphatase (ALP) activity. The pasteurised milk should be ALP negative, as this enzyme is destroyed during the pasteurisation process.

Question 17

What do you think the effects of pasteurisation are on the safety of milk…and its nutritional value?

Answer 17

The impact of pasteurisation on nutritional value of milk is of limited, if any, significance. The amount of vitamin C is reduced slightly (by about 20%), and some vitamin levels are reduced (thiamine and vitamin B12 are reduced by ~10%). There is a reduced ‘cream line’ due to disaggregation of fat globules…but the major significance of pasteurisation is on the milk microbiology. Important pathogens are removed during pasteurisation and include Mycobacterium tuberculosis (TB), with no evidence that TB infections have been acquired through recent consumption of contaminated milk. However, other pathogens such as Mycobacterium avium paratuberculosis (MAP), the cause of Johne’s Disease in cattle that may have a link with Crohn’s Disease in humans, is more of a challenge and there is concern that MAP bacteria could survive the pasteurisation process, although research to date suggests that this is likely to present a low risk.

Question 18

What are the drinking milk standards for raw cow’s milk compared to heat-treated milk?

Answer 18

A comparison of the standards for raw versus heat-treated milk highlights the difference between the requirements for pathogenic micro-organisms and coliforms…although raw milk MUST be negative for Salmonella spp. (5 samples 25ml negative)

Question 19

What are your thoughts on the risks versus potential benefits of drinking raw milk?

Answer 19

There is no doubt that the raw milk topic often produces some lively debate, but we must bear in mind the potential health hazards will far outweigh the benefits, as the latter are largely based around taste as nutritional effects are minor and other reported beneficial side effects such as reduced risk of asthma are not proven. Apart from zoonotic infections such as Salmonella spp. and Listeria spp., the main hazard will be TB, particularly if drinking raw milk from herds in endemically affected areas where prevalence in the cattle population is likely to be quite high (can you remember the distribution of TB infected herds in the UK?). Despite frequent TB testing of dairy herds, test sensitivity is only around 70% at best, and there always remains a small chance that an infected cow could have widespread TB infection, including dissemination to the udder…

Question 20

Using the below headings, can you think of potential problems that may occur during processing – and the actions required to address these?

1. Arrival of raw milk
2. Storage in silo <5 degrees celcius
3. Pasteurisation
4. Cooling to 10degrees celcius
5. Hold
6. Filling cartons
7. Cold storage

Answer 20