Effect of dry period versus continuous milking on periparturient concentrations of bovine prolactin in milk from half udders.

Four multiparous cows were used to determine whether continuous twice daily milking of half the udder throughout the dry period would alter the prepartum accumulation of prolactin in secreted milk. The control half of each udder was allowed a dry period of 43 d, and twice daily milking was reinitiated in this half udder 11 d before parturition, whereas the treated half was milked continuously throughout. Milk from the treated half decreased to very low yields despite continuous milking, whereas concentrations of prolactin in milk remained low and without much day-to-day variation within each cow. Concentrations of prolactin in milk and yields of milk increased during the week before parturition in both halves of the udder, but there were no significant differences due to previous continuous milking. Therefore, prepartum accumulation of high concentrations of prolactin in secreted milk did not appear to depend on prior occurrence of a dry period. Elevated concentrations of prolactin in milk declined rapidly and equally in each half udder after parturition.