I don't actually have first hand knowledge but slaughtering livestock just for adrenal glands simply makes no sense. A meat processing facility will buy livestock, slaughter them, process them and then sell the various components. There's a certain demand by companies making compounds such as epinephrine for animal parts used in synthesis. They will go through a supplier that will purchase animal parts from meat processor that they know they can sell at a certain price. I'm sure for at least some meat processors it's more lucrative to separate out kidneys with adrenal glands to sell separately at a higher price than e.g. just sell them together with all the rest to a company making dog food.