Final answer:
The mother produces the hormone prolactin to maintain the ability to produce milk after birth, which is stimulated by the suckling of the baby and maintained through frequent breastfeeding or pumping.
Step-by-step explanation:
The hormone that the mother produces to maintain the changes in the breast and therefore the ability to produce milk after birth is prolactin. After the baby begins suckling at the breast, signals sent to the hypothalamus trigger the release of prolactin from the anterior pituitary gland, which then causes the mammary glands to produce milk. While oxytocin is also released, aiding in the milk's release, prolactin is primarily responsible for the synthesis and maintenance of milk supply.
It is interesting to note that the prolactin-mediated synthesis of milk changes over time, and its levels remain high for several months if frequent milk removal through breastfeeding or pumping is practiced. However, even if breastfeeding continues, the baseline prolactin levels will eventually return to pre-pregnancy levels. A range of other hormones, including growth hormone, cortisol, parathyroid hormone, and insulin, also support lactation by facilitating the transport of nutrients to the breast milk.