Final answer:
The hormone used to increase milk production in lactating cows is called prolactin (PRL), which is essential for initiating and maintaining breast milk supply.
Step-by-step explanation:
The hormone used to increase milk production in lactating cows is called prolactin (PRL). This hormone is produced by the anterior pituitary gland and is crucial for the establishment and maintenance of breast milk supply. Prolactin operates through a positive feedback loop where the suckling action of the calf stimulates the mother's mammary glands to produce milk, promoting more prolactin release. The process of lactation involves additional hormones including growth hormone, cortisol, parathyroid hormone, and insulin, all of which help in providing the necessary nutrients through the mother's blood to the milk.