ALLENDALE, Mich. — Rick Sietsema, co-owner of Sietsema Farms, would like to know just how contaminated feed ended up on his farms. Sietsema Farms, with seven locations in Michigan, was the farm where 50,000 turkeys were killed last August after they ate feed contaminated with Lascadoil, an industrial waste oil that contains trace amounts of lasalocid, a drug that’s been approved for use on poultry and other livestock.

Lascadoil is a byproduct of lasalocid production and isn’t supposed to be fed to animals. Zoetis, the maker of lasalocid, sells the waste oil to a company to be disposed of with the stipulation that it only be used in the production of biofuel. Sietsema said he usually buys the grease he uses in feed from a local company, which he wouldn’t name. "I’m looking forward to FDA (U.S. Food and Drug Administration) getting this completed so we can find out exactly what happened," he said. "I want to make sure the story gets out clear exactly what happened. I don’t want our farms to be blamed."

Sietsema said he experienced "significant mortality" of birds at five of his farms over the weekend of Aug. 10-11 of last year, but said entire flocks didn’t die, as some reports have indicated.

"We were able to nip this in the bud by working with the Michigan Department of Agriculture and Rural Development (MDARD) and federal authorities," he added. "We strive to do the best turkey production in the world. Our farms are top-notch farms in the country.

"I’m disappointed that contaminated feed made it to this farm. I’m the lottery winner for a bad load of product." When asked how the incident affected his operation, he remarked, "When you lose a seven-figure number of livestock, it hurts. If half your house burned down, would you be impacted by it?"

He added the FDA has told him every month since October it would have its investigation completed by the end of that month. Last week the FDA issued a statement about the incident. In general, it regulates animal drugs, animal feeds and foods produced by animals, the FDA statement said. USDA plays a lead role in regulating aspects of some meat, poultry and egg products.

The two agencies have worked closely with MDARD, the statement added; MDARD took "extraordinary steps" to ensure that animals potentially exposed to Lascadoil did not enter the food supply.

"The turkeys at Sietsema Farm Feeds that were exposed to feed contaminated with Lascadoil died before they made it to market and exposed hogs were subjected to the recommended 28-day withdrawal period before going to slaughter," the FDA stated further.

Another company, Shur-Green Farms of Ansonia, Ohio, appears to have been involved in the incident, but the extent and exact nature of its involvement is not clear. Shur-Green is an organic waste and materials recycling firm.

Last October the company issued a voluntary nationwide recall of soy oil containing Lascadoil. The company notice stated the product was meant for non-food use, but may have ended up in animal feed. It said the recall was triggered by the death of turkeys. The notice was posted on the FDA’s website with the FDA’s knowledge and dated Oct. 23, 2014.

About 20,000 hogs at Sietsema Farms were also fed the contaminated feed, but apparently none of them died from the exposure. Lasalocid is not approved for use in pigs, and Sietsema said he would never deliberately feed his pigs anything with lasalocid in it.

The FDA is supposed to issue a report about the incident, but it’s not clear yet when that will happen.