Researchers keep milk free of contaminants

Sep 8 2004

Dairy farms in the United States produced more than 170 billion pounds of milk last year. The more than 9 million cows that produced that milk occasionally need to be treated for various ailments, so researchers at North Carolina State University’s College of Veterinary Medicine are working to protect that important commodity by helping to keep contaminants out of the milk supply.

Dr. Geof Smith, assistant professor of ruminant medicine, is studying how long the residue of pharmaceuticals remains in cow’s milk. When a dairy cow is given antibiotics or other drugs, the milk that cow produces must be discarded until the drugs clear the cow’s mammary system.

Smith’s work is part of the Food Animal Residue Avoidance Data Bank (FARAD), a support system designed to provide livestock producers and veterinarians with information on how to avoid drug, pesticide and environmental contaminant residue problems. FARAD is a nationally funded program that is administered by three universities – NC State, the University of Florida and the University of California-Davis.

At issue is the antibiotic Ceftiofur, which is used to treat a number of problems in cows such as respiratory disease, pneumonia and lameness. Ceftiofur is approved for injection into the muscle and under the skin, but, according to Smith, some farmers have injected Ceftiofur directly into the mammary glands to treat mastitis – an infection of the mammary gland.

“That led to several violations when residue of the drug showed up in the milk of several dairy farms. There were several cases that were referred through FARAD of large losses of milk that had to be dumped because of Ceftiofur residue,” Smith said.

Smith and his colleagues at FARAD, including Drs. Jim Riviere, Ron Baynes, and Ronette Gehring, have just concluded a study that specifically addressed the practice of injecting Ceftiofur directly into the quarters, or mammary glands, to treat mastitis. Smith’s findings have just been published in the Journal of the American Veterinary Medical Association. “Until now, there’s been no data telling us how long that drug residue remains,” Smith said.

While there is no special issue with Ceftiofur that makes it dangerous to humans, Smith says the study is part of the effort to keep drugs out of the human food supply unless they are totally inert. “There are also drug allergy issues. It’s best to avoid any and all contamination of the food supply,” he said.

Smith’s research involved using the drug in five dairy cows located on the NC State dairy farm. “We took milk samples at milking time twice a day, for 10 days,” Smith said.

Smith then used chromatography analysis to measure the drug’s concentration in the milk and determine how long it remained present. The researchers found that Ceftiofur disappears after about seven days. “That’s longer than a lot of drugs. With some of the other drugs labeled to treat mastitis you only have to throw the milk away for 36 to 48 hours,” he said.

“Seven days is a long time, but sometimes mastitis doesn’t respond well to the other drugs. It’s better to throw away the milk from one cow for seven days than to risk contaminating an entire tanker truck of milk and face a fine of maybe six, seven or eight thousand dollars,” he said.

Smith’s study cost only $10,000 – the most expensive portion was the analysis of the data on a specialized chromatography machine. “With some rare exceptions we need to avoid expensive studies because there just isn’t the funding that there used to be. We try to be as efficient as possible,” Smith said.

“There’s been a lot of positive feedback on the research. It’s very practical and the USDA has recommended that FARAD continue this type of research. It’s research that needed to be done,” Smith said.