Question

Which hormone causes milk letdown in dairy cows?

• A. Prolactin
• B. Estrogen
• C. Oxytocin
• D. Progesterone

Hint:

Prolactin = produce milk; Oxytocin = release milk. Don’t mix these up!

Answer 1

The Correct Option is C

Milk production and milk ejection are regulated by different hormones. Prolactin stimulates the alveolar cells to produce milk. Oxytocin, secreted from the posterior pituitary gland, causes contraction of myoepithelial cells around the alveoli, pushing milk into the ducts so it can be removed during milking. Estrogen and progesterone prepare the udder during pregnancy but do not cause milk letdown. Stress inhibits oxytocin release — that’s why calm milking is essential.

Answer 2

Process of Elimination: The question asks specifically about milk RELEASE, not milk production — an easy trap.

Prolactin makes milk (production), so it's tempting but wrong for this question. Estrogen and progesterone are pregnancy hormones that prepare the udder, not trigger letdown.

That leaves Oxytocin, which contracts the myoepithelial cells around the alveoli to physically push milk into the ducts — the actual 'letdown' reflex.