The benefits of ensuring milk let-down has occurred include improved milking efficiency and maximised milk production.

Slow milking time and incomplete milking out are indicators of interrupted milk let down.

• Agitated, fearful or stressed cows produce the hormone adrenaline which counteracts the activity of oxytocin and inhibits let down. It may take 20-30 minutes for the effects of adrenaline to subside.
• Pain during the milking process will affect milk let down. Ensure any udder conditions are treated and milking machinery is not hurting cows.

An understanding of how milk let down occurs will help milkers manage the milking process in a way which encourages it and cows that let down just prior to cup attachment will milk out more completely.

• So how does let-down occur?

  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.

  

  Anatomy of a teat

  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 let down 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 let down has been initiated. Cows with well-filled udders require a shorter period of stimulation to elicit a milk let down 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 let down 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 let down has started to make full use of the increased udder pressure that occurs.

• Do your cows have a let-down problem?

  

  Damage to the teat end (Hyperkeratosis). This can be caused by over-milking due to poor let down.

  If any of the following are occurring, then your cow may have a milk let-down problem:

  • 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.
  • 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 let down at this milking.
  • Damage to the teat end.

• How can I ensure my cows don't have let-down problems?

  Avoiding the following stressful situations will help ensure good milk let-down.

  • 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 or twisting tails and noisess, i.e. yelling or loud music.
  • Animal health problems e.g. mastitis, lameness.
  • Stray voltage.