Hormone Responsible for Milk Hold-Up

The hormone responsible for holding up of milk is:

Correct Answer: Epinephrine (Adrenaline)

Epinephrine (Adrenaline) is the hormone responsible for holding up of milk (milk inhibition/suppression of milk let-down). It is released during stress, fear, or excitement and causes vasoconstriction of udder blood vessels, preventing oxytocin from reaching the myoepithelial cells.

Contrast: Oxytocin vs. Epinephrine

• Oxytocin: The milk let-down hormone — it causes contraction of myoepithelial cells surrounding alveoli, pushing milk into cisterns and ducts.
• Epinephrine: The milk hold-up hormone — antagonizes oxytocin action; released during stress/pain/fear.

Practical Implication

This is why milking should be done in a calm, stress-free environment. Any disturbance (loud noise, pain, new milker) causes epinephrine release and the cow withholds milk — even if she has been milked partially.

Residual Milk

Residual milk (milk left in udder after normal milking) can only be obtained after oxytocin injection or by re-milking.

Why Other Options Are Wrong

• Oxytocin → causes milk let-down (opposite function).
• Vasopressin → antidiuretic hormone; not directly related to milk ejection.
• Calcitonin → regulates calcium metabolism; not involved in milk ejection reflex.