Enhancing milk let-down

How milk letdown occurs

An understanding of how milk letdown occurs will help milkers manage the milking process in a way which encourages it. Cows that letdown just prior to cup attachment will milk out more completely. Milk is initially secreted into small sacs within the mammary gland called alveoli, it is from here that it is ejected for consumption or harvesting.

Mammary alveoli are surrounded by smooth muscle cells which are a prominent target cell for oxytocin. Oxytocin stimulates contraction of these cells, causing milk to be ejected into the ducts and cisterns above the teat.

Oxytocin is released after the cow receives an appropriate stimulus - this can be visual, aural or physical, and should be predictable and consistent at every milking. Handling/massage of the teats for at least 15sec is a strong stimulus, but cows can also learn to letdown through the association of the dairy environment to the milking process.

The pressure of milk being forced into the ducts/cistern and down towards the teat causes the teat to swell with milk and become ‘plump’. It takes 60 - 90 seconds for teats to become plump after letdown has been initiated. Cows with well-filled udders require a shorter period of stimulation to elicit a milk letdown response than cows with less-filled udders.

The action of oxytocin is essential for emptying of the udder during milking. As much as 80% of a cow’s milk is unavailable if this oxytocin release is insufficient or does not occur.

Its letdown action lasts for about 5 minutes and is strongest for the first 3 minutes of milking. It is important to get the cups attached quickly after letdown has started to make full use of the increased udder pressure that occurs.

• No milk flow when the cluster has been attached for greater than 2 minutes in late lactation, sooner in early lactation.
• Cows are agitated during milking. Agitated, fearful or stressed cows produce the hormone adrenaline which counteracts the activity of oxytocin and inhibits letdown. It may take 20-30 minutes for the effects of adrenaline to subside.
• Milk flow is ending when there is still a significant amount of milk in the udder.
• Flow can be interrupted part way through milking - in this case the milk flow at the start of milking is residual milk left in the cistern from the end of the previous milking and not milk which has been letdown at this milking.
• Damage to the teat end.
• Pain during the milking process will affect milk letdown. Ensure any udder conditions are treated and milking machinery is not hurting cows.

Ensuring smooth milk letdown

Avoiding the following stressful situations will help ensure good milk letdown.

• Inconsistent milking routines.
• Bad pipework design or maintenance which hurts cows.
• Poor machine set up or maintenance.
• Poor animal handling techniques such as: hitting cows, twisting tails or intimidating noises, i.e. yelling or loud music.
• Animal health problems e.g. mastitis, lameness.
• Stray voltage.

The impact of fear on letdown

Fear causes the release of the hormone adrenaline into the blood stream causing a ‘fight or flight’ response.

Adrenaline primes the body for action by increasing the heart rate and blood flow to the muscles. It also blocks the action of the milk letdown hormone oxytocin. This effect can last up to 30 minutes from a single release of adrenaline.

There are a number of factors that provoke fear in cows including: fear of heights; sudden movements and noises; threatening or aggressive actions; prolonged eye contact; and large or towering objects. Fear responses should be minimised by appropriate handling behaviour and good dairy design.

The effects of fear can have a significant impact on the efficiency and productivity of the milk harvesting system and result in the following,

• Handling becomes harder, more time consuming and more dangerous.
• Milk yield declines.
• Milk letdown is impaired.
• Cows become more prone to injuries.
• Welfare is compromised.

Address welfare issues. Pain, stress and fear are all animal welfare issues and need to be avoided if possible. Not only are they ethically unacceptable, but also there are local community and international market expectations to meet.

Stockmanship in the dairy

Good dairy stockmanship not only improves animal health, milk letdown and production, it helps ensure a safe and efficient work environment for the whole team.

Cows have good short-term and long-term memories and will readily learn a variety of tasks. This characteristic is one reason why cattle respond well to consistent handling routines.

Strong physical or emotional experiences (good food, fear, pain) are likely to result in long lasting memories. Cattle learn to associate people or locations with rewarding or negative experiences.

How to promote calmness in cows

• Avoid hits, slaps and tail twists as they all provoke fear, even when they are not forceful. Research has shown that negative handling of heifers increases fear of humans and flight distances.
• Avoid sudden or unusual movements that will cause a fearful response.
• Avoid shouting or behaving in a threatening manner. Entering into the flight zone will provoke fear especially if the cow cannot move away.
• The degree of fear a cow experiences is intensified in an unfamiliar environment or circumstance. It is important to keep features such as lighting, floor surfaces or levels and fence or wall types as consistent as possible.
• Prevent painful milkings e.g. due to poor machine set up, incidences of mastitis or poor handling (e.g. hitting), and avoid painful procedures in the dairy at all times.
• Ensure milking machines are maintained and stray voltage is eliminated.
• Give some supplementary feed as a reward after bad experiences such as restraining or health related procedures.
• Keep the milking routine calm and consistent. This means that all milkers need to know the milking routine. It should be written down and communicated to any new milkers.
• Put bends on pipes to avoid cow injury and jammed wash down hoses.

Benefits of a safe dairy environment

Creating a good environment in the dairy is key to an efficient milking.

The advantages of a good and safe dairy environment include:

• Maximise cow flow and smooth movement
• Reduce lameness and injuries
• Address welfare issues
• Less fear in the animals
• Better production and speed of letdown

Cows are creatures of habit and they respond better if they have a routine that is consistent and predictable. While an unfamiliar feature of the dairy may initially provoke moderate fear, cows will learn to become familiar with that feature over time. If factors are constantly changing, a cow will not be able to adjust and the cow's sensitivity will be heightened, making the cow overly fearful of people or particular location or physical structure.