Milk production in Holstein cows is driven by tightly regulated endocrine control that coordinates mammary development, onset of secretion, maintenance of yield and milk ejection. Along the reproduction-lactation axis, four phases are recognized: mammogenesis (late gestation), lactogenesis (peripartum; phase 1 secretory differentiation and phase 2 secretory activation), galactopoiesis (yield maintenance largely governed by the somatotropin‑IGF‑1 axis) and milk ejection (an oxytocin-dependent neuroendocrine reflex that can be impaired by acute stress). Local autocrine regulation, especially the feedback inhibitor of lactation (FIL) and intraluminal pressure, decreases secretion when milk removal is incomplete and contributes to controlled involution during dry-off. Postpartum negative energy balance and increased hepatic steroid clearance modulate estradiol and progesterone profiles, delaying ovarian cyclicity and potentially compromising fertility.
Frunză et al. (Thu,) studied this question.