KANSAS CITY, Mo. – A recently published research study indicates that the number of cattle deaths linked to beta-agonists may be higher than reported, maker of the drug. The study was published inPLOS ONE, a scientific journal.

Researchers from Texas Tech Univ. and Kansas State Univ. found that between 2011 and 2012 more than 3,800 cattle in 10 feedlots that were fed the drugs died. The study noted that 40 percent to 50 percent of those deaths were attributed to administration of the drug.

"While death is a rare event in feedlot cattle, the data reported herein provide compelling evidence that mortality is nevertheless increased in response to administration of FDA-approved βAA (β-adrenergic agonists) and represents a heretofore unquantified adverse drug event," researchers wrote.

Merck & Co., which makes Zilmax and Elanco Animal Health, which makes ractopamine, criticized the researchers' methodologyand noted that the feed additives are approved by the Food and Drug Administration.

Beta-agonists are credited with improving beef production efficiency. Growth promotant drugs such as zilpaterol hydrochloride-based Zilmax can add 24 to 33 lbs. of live weight to steers and heifers in their last 20 days of time on feed. But questions about the safety of the drug came to light when Tyson Foods Inc., in August 2013, announced the company would no longer purchase cattle fed with Zilmax on concerns that the drug was causing lameness in some cattle.

The researchers noted in the study that "we believe a broad and inclusive dialogue that explores the balance between improved production efficiencies achieved through means such as βAA and resultant adverse effects on the welfare of animals we raise for food is needed. This is particularly warranted for those drugs that are approved solely to improve the efficiencies of production yet offer no offsetting health benefits to the animals to which it is administered. For this dialogue to be sufficiently inclusive, it ought to include a broad collection of stakeholders such as animal scientists, cattle and beef producers, animal health specialists, welfarists, ethologists, and consumers."

The study is co-authored by Guy Loneragan, a professor of food safety and public health at Texas Tech, and Daniel Thomspon and Morgan Scott of Kansas State. The study is titled "Increased Mortality in Groups of Cattle Administered the β-Adrenergic Agonists Ractopamine Hydrochloride and Zilpaterol Hydrochloride".