Nov 5 (Reuters) - Merck & Co Inc said a comprehensive review it undertook showed that its controversial feed additive Zilmax was safe when used according to its product label.

Merck suspended sales of Zilmax in the United States and Canada in August last year following concerns about animals showing signs of distress after use of the weight-gain product.

A study published in March suggested that the number of U.S. cattle deaths that may be linked to Zilmax are much higher than the figures reported by the drug company to the federal government.

Merck said on Wednesday that the review by its advisory board was conducted after concerns that cattle could consume more Zilmax than approved.

An updated Zilmax label, with a lower dose, was approved by the U.S. Food and Drug Administration, Merck Animal Health said.

Merck wants to feed Zilmax to 240,000 U.S. cattle to prove it is safe. But giant meat processors like Cargill Inc and Tyson Foods Inc don't want to touch animals fed with the drug, Reuters reported in April.

Merck Animal Health also filed to update Zilmax's label in Canada, it added.

Merck's shares were up 1.2 percent at $60.08 on the New York Stock Exchange in early trading on Wednesday.

(Reporting by Natalie Grover in Bangalore)