Do cows produce milk all of the time or only when pregnant like other mammals?
Lactation (milk production) is stimulated from synthesis to “let down” from the mammary alveoli in response to oxytocin, a hormone released in response to neural or mechanical stimulation (when the areola around the top of the teat is compressed), whose mode of action in letdown is to increase intramammary pressure driving milk from the secretory epithelial cells to the alveolar lumen, where gravity does its job.
