Principles of Dairy Production

The Dairy Animal - Facts & Figures

Birth & Puberty

A female calve (destined for dairying) weigh approx 40kg at birth.
If reared correctly, she should reach puberty at 1 year, weighing 250kg.

Oestrous Cycle & Gestation

The length of the oestrous cycle of a cow is 21 days and it lasts an average of 18 hours.
The gestation period of the dairy cow is 283 days (approx 9.5 months)

Lactation

Lactation is the production of milk in mammals.
A cow commences producing milk as soon as she has a calf.
If the cow is used to suckle calves, then she may continue to produce milk for up to 2 years.
If she becomes pregnant (in-calf) she will go dry two months before calving.
In commercial milk production, the aim is have the cow calve once a year, around the same time each year.
This means that she will be milking 10 months of the year or approx 305 days.
The diagram below, the Lactation Curve, outlines how the production of milk over these 10 months varies considerably.

Lactation Yields

The milk yield of the cow depends on the breed.
Holstein: 8000kg per year
Jersey: 5500kg per year
Friesian: 6600kg per year.
These vary significantly even amongst individual cows – A Friesian may vary from 2000kg a year to 12000kg of milk a year.
These yields have also increases over the last number of years in Ireland due to better selection of breeds.
Find out more about the various dairy breeds by clicking below.

Milk Let Down Process

The production of milk occurs in the udders of a cow.
The udder contains tissue called alveoli which produce the milk.
The production is milk occurs after birth when high levels of the hormone oxytocin are produced.
The production of milk is a reflex action and is triggered by suckling on the udder or by artificial milking.
The nerves in the udder cause hormones to be released into your bloodstream.
One of these hormones (prolactin) acts on the milk-making tissues.
The other hormone (oxytocin) causes the breast to push out or ‘let down’ the milk.
The let-down reflex makes the milk in the udder available for collection.
Cells around the alveoli contract and squeeze out the milk, pushing it down the ducts towards the nipple.
Oxytocin also makes the milk ducts widen, making it easier for the milk to flow down them.
Oxytocin can also be released by the sound of the milking machine or by the presence of a calf.

Frequency of Milking

Milking empties the udder of the cow, which stimulates milk-secreting alveoli to commence producing milk.
Frequently milked cows produce more milk than those milked irregularly.
Therefore a cow milked four times a day will produce more milk than a cow milked twice – it will work to demand.
BUT milking more than twice a day is uneconomical and leaves cows more prone to disease such as mastitis.
With milking twice daily, the ideal milking interval is 12 hours. This gives the cow less stress and will get the highest yields.
But this gives the farmer a very long working day and is uncommon. The most common intervals are 14/10 or 13/11 hour intervals.

Milk Composition

Milk used for bottling or drinking must by law contain 3.6% fat and 8.5% SNF.
Creameries buy milk in many different ways – sometimes at a flat rate per kg.
Sometimes, however, it may be by percentage butterfat or protein.
Milk composition varies also amongst different breeds also.
The milk of the Jersey cow has the highest butterfat and SNF content of any cow.
Also the composition of milk varies during milking.
The milk at the start may only contain 1% fat, while the milk at the end (“The Stripping”) may contain 10% fat.

Hygiene and Milk Quality

Dirty milk (containing dirt, bacteria or antibiotics) can cause serious problems when processing.
Dirty milk is caused by unhygienic milking machines or poor milk filters.
Antibiotics are found in milk as residues from treatments to cows for mastitis.
When milk is found to be not up to standard, it may be rejected by the creamery or bought at a lower price.
The density of milk is measured at the creamery to insure famers have not diluted it. In the laboratory a lactometer (shown across) or a refractometer can be used.
Milk is also tested to determine the Total Bacterial Count (the number of bacteria in the milk) and the Somatic Cell Count (the number of body cells, mainly white blood cells, in the milk). This is used to determine if an infection may be present in the udder.
The table below summarises the tests performed on milk at creameries.

Specified Practical Activity

Processing Milk

Milk is normally processed before selling to the consumer.
Most milk goes through pasteurisation, a process by which milk is heated to 71.7^oC for 15 - 25 seconds and the cooled rapidly to 3^oC.
This kills 99.9% of the bacteria present in the milk.
Milk is also homogenised which removes large globules of fat, distributing the fat (cream) evenly through the milk (the fat normal rises to the top of the milk) and creates a consistent smooth texture in the milk.
Raw Milk is unprocessed milk, which is not pasteurised or homogenised, and is seen as a niche foodstuff.

The Milking Machine / Milking Parlour

A milking machine is used for extract the milk from the cow's udder and is designed to simulate the suckling process.
Milking machines contain a series of milking cluster units, which attach to the four teats of the udder.
A pump is used to create a vacuum to 1. stimulate the teat and 2. transfer the milk to a storage vessel.

Cluster Attached to Cow
A Milking Machine Cluster Unit

There are various designs for milking parlours.
The Herringbone design is the most commonly used in Ireland and features a lowered floor in which the farmer works, giving easy access to the cow's udders.
Rotary milking parlours are becoming increasingly popular, as herd sizes increase.e
These feature a round design which rotates slowly on a platform. The time taken to rotate equates to the average time needed to milk a cow.
Rotary milking parlours are more efficient than herringbone designs and reduce milking time for large herds.
Many milking parlours now feature large amounts of automation: the attachment / detachment of the clusters, udder disinfection, cleaning of the clusters, feeding of the animals.
These are often called robotic milking parlours.

A Herringbone Milking Parlour
A Rotary Milking Parlour (Robotic)

Liquid Milk vs Manufacturing (Creamery) Milk

As we have already seen, milk production is seasonal with most of the milk produced over the spring and summer months.
Cows only lactate for 10 months which means, if all calves are born in the spring, no fresh milk would be produced over the winter months of December or January.
Some farmers in Ireland specialise in producing liquid milk for bottling all year round and employ a mixture of spring calving and autumn calving to achieve this.
There are increased costs associated with doing this so they are compensated accordingly.

Liquid milk production involves both spring and autumn calving to ensure a continuous supply of fresh milk for bottling over the winter months. There are higher feed costs associated with liquid milk production but farmers generally receive higher prices for their milk. Liquid milk production is often associated with targets for quantity of milk, rather than quality.

Farmers who employ spring calving only produce milk for 10 months of the year and generally sell their milk to milk processors (creameries) as manufacturing milk.
Manufacturing milk is milk used to make dairy products like butter, cheese, milk powder or yogurt and isn't used for bottling.
Employing a spring calving system keeps costs low as grass provides most of the cow's feed.
Farmers who produce milk for manufacturing often focus on milk quality (% fat & protein) rather than quantity or volume.

Manufacturing milk is used to produce dairy products like cheese, butter, yogurt or milk powder and is sold to milk processors on the basis of its quality (% fat and protein). Farmers who produce manufacturing milk employ spring calving systems and produce milk for 10 months of the year.

Milk Prices

Most farmers produce manufacturing milk and are paid on the basis of its quality (% fat and protein).
The general formula for calculating the price of milk is known as A + B - C.
A represents the price received for the protein content in the milk.
B represents the price received for fat content in the milk.
C is the manufacturing cost.
The creamery may also issue bonuses (e.g. for producing milk in the winter months) or penalties (e.g. high total bacterial count or somatic cell count).

Milk Price Calculator: A + B - C

A = Fixed protein value

B = Fixed fat value

C = Manufacturing cost

Price of Milk = (A x % protein + B x % Fat) - Cost - C

Example 1

In example 1, the famers is producing milk with 3.3% protein (5.466c is the fixed protein value) and 3.6% fat (4.218c is the fixed fat value). There is a manufacturing charge of -4c on each litre and the farmers receive a bonus of 0.45c on each litre also. This may be for their cooling capacity or for the time of the year. VAT (Value Added Tax) is applied to the milk also. The farmer receives 31.27c per litre.

Example 2

In example 2, the famers is producing milk with 3.46% protein (5.466c is still the fixed protein value) and 4.01% fat (4.218c is still the fixed fat value). Again, there is a manufacturing charge of -4c on each litre and the farmers receive a bonus of 0.45c on each litre also. The farmer receives 34.01c per litre.

Example 3

In example 3, the famers is producing milk with 3.78% protein (5.466c is the fixed protein value) and 3.29% fat (4.218c is the fixed fat value). There is a manufacturing charge of -4c on each litre but the farmer has received a penalty on his milk (e.g. high somatic cell count or dirt etc). The farmer receives 32.04c per litre.

Comparing Liquid Milk & Manufacturing Milk

Recommended Video - Profile of a Dairy Farm

Virtual Farm Yard Tour - Rotary Milk Parlour