CHICAGO, Oct 30: US drugmaker Merck & Co told Reuters yesterday that it plans to bring its Zilmax animal feed additive back for sale in the United States and Canada, after it completes an audit of how the muscle-building cattle feed product is used in the agriculture sector. A spokeswoman for the company’s Merck Animal Health unit said that while “it is too early to speculate on when we will resume sales for Zilmax in the US and Canada,” Merck was pushing forward with its quality control program to ensure the weight-adding drug is being properly used. (agencies)