Lactation starts with active contraction of the myoepithelial cells surrounding the alveoli, this process is termed milk ejection, or milk let down. These myoepithelial cells contract when stimulated by oxytocin, a hormone released from the neurohypophysis of the pituitary as a result of a neuro-endocrine reflex. The afferent side of the reflex consists of sensory nerves from the mammary glands, particularly the nipples or teats. Afferent information reaches the hypothalamus, which regulates the release of oxytocin from the neurohypophysis. The milk ejection reflex can be stimulated by suckling, concentrate feeding, barn noises, and the sight of the calf. It can also be inhibited by emotionally disturbing stimuli, such as dog barking, outer loud and unusual noises, excess muscular activity, and pain. Stressful stimuli increase the activity of the sympathetic nervous system (epinephrine and norepinephrin) which can inhibit the milk ejection reflex. | Neurohormonal control of lactation and milk let-down in dairy animals
