Health Canada monitoring reports of lameness in U.S. cattle fed with Zilmax Health Canada says it's keeping an eye on reports from the U.S. that a supplement designed to bulk up cattle before slaughter may be causing the animals lameness or difficulty in moving. The Canadian health regulator said it has not received any reports of adverse reactions among cattle being fed with Zilmax in the Canadian marketplace, but it's communicating with the makers of the drug to stay "apprised of the situation." Health Canada is also working with the U.S. Food and Drug Administration to "ensure a collaborative approach," the agency says in an email. Merck & Co. (NYSE:MRK) announced Friday that it was temporarily suspending sales of Zilmax, which contains zilpaterol, in Canada and the U.S. pending a safety review. The drugmaker said it will be closely tracking cattle that have been fed with the supplement from the feeding yard to the slaughterhouse to determine what's causing the reported mobility issues. Merck said sales of Zilmax in Canada and the U.S. totalled $159-million last year. "We're in constant links with Health Canada," Merck spokeswoman Ani Armenian said in an interview Monday. The safety audit that is being run by Merck is taking into account mostly U.S.-based organizations or people, but there might be the possibility that Canada might be involved. Food giant Tyson Foods Inc. said last week it will no longer accept cattle that have been fed with the additive after noticing some of them were having difficulty walking. Meanwhile, international food producer Cargill said it would continue accepting Zilmax-fed cattle, including at its Canadian facilities. "We believe the actions taken by Merck are prudent, although Cargill has not experienced the same animal well-being situations as others in using this product," Cargill spokesman Mike Martin said in an email. The company said all of the cattle in its supply chain, both in Canada and the U.S., that are being fed the supplement will be processed at its beef plants by the end of September. Martin said the issue is one of animal well-being, not food safety. "We are encouraged by this collaborative effort to seek facts that will be shared throughout the industry," said Martin.