This hormone was approved after fewer than five years of testing, with no long term studies of its effect either on the animals themselves or on human beings who consume milk from these animals. The American public over then next fifteen or twenty years will provide information for the field studies. On the basis of these tests they have approved the hormone for general use on the dairy herds of America.
European countries have by and large rejected the use of such artificial stimulants.
Like the US, they already produce more milk and milk products than they can consume, and have to artificially support the price of milk with government subsidies in order to prevent the over-supply from collapsing the price and leading to the failure of numerous small farms. Gee, I wonder who stands to make money out of this. I don't think so. In fact, they are more likely than ever to be run out of business by the industrialized factory farms where economies of scale make a much greater difference in profitability. The cows are unlikely to benefit.