Editor's note: The following information is excerpted from a U.S. Food and Drug Administration news release.
A new method is available for testing animal feed for prohibited materials.
The method relies on polymerase chain reaction (PCR), a molecular technique that amplifies small amounts of genetic material to produce larger amounts for analysis. Once the new PCR-based method is routinely used, it will enhance the U.S. Food and Drug Administration's ability to make sure animal feed is safe and free of prohibited materials that may spread the agent thought to cause bovine spongiform encephalopathy (BSE).
In 1997, the FDA prohibited most mammalian protein from being used to make animal feed for ruminants. In April 2008, the FDA strengthened the feed ban by prohibiting high-risk materials from being used to make all animal feed, including pet food. High-risk materials are those materials from cattle that have the highest chance of carrying the agent thought to cause BSE, such as the brains and spinal cords from cattle that are 30 months of age or older.
To make sure animal-feed manufacturers comply with the feed ban, the FDA tests feed samples for prohibited materials. Feed samples are typically collected by field investigators in the Office of Regulatory Affairs, the FDA's investigative arm. The samples are analyzed by feed microscopy, a technique that uses a microscope to visually identify the components in the sample. Samples that test positive for a prohibited mammalian protein then undergo PCR-testing to confirm the positive result.
For years, feed analysts used feed-microscopy methods to detect mammalian protein in animal feed. But these methods have various limitations.
In 2009, the Office of Research of the FDA's Center for Veterinary Medicine developed a faster, simpler method based on real-time PCR. In real-time PCR, a fluorescent dye is used to tell how much genetic material or DNA is being produced during the reaction. The fluorescent dye binds to the DNA, and the bound DNA fluoresces and emits a light signal that is detected by the PCR instrument.
An important criterion was the ability of the new method to detect mammalian protein when present in animal feed at a concentration of at least 0.1 percent.
The new real-time PCR-based method met strict requirements for sensitivity (ability to detect true positive samples), selectivity (ability to detect true negative samples), and specificity (ability to detect only the targeted animal species).
After strict in-house testing, the new method underwent a peer-verification trial to assess how well it worked when used by other laboratories and if the instructions on how to use it were clear. Two outside laboratories participated in the peer-verification trial. The results showed that the method had 100 percent specificity in identifying three types of prohibited materials, such as cattle meat-and-bone meal, lamb meal, and goat meat meal. There was only a 0.6 percent rate of false positive results.
The peer verification trial proved that the new real-time PCR-based method can easily and reliably be used by other laboratories.
In less than 2.5 hours, the new real-time PCR-based method can detect processed materials from cattle, sheep, and goats, as well as a select set of processed materials from chickens, turkeys, and geese.
The new 2009 real-time PCR-based method will become the FDA's "one-stop shop" for testing animal feed. It will replace feed microscopy as the FDA's method of choice for screening animal feed for prohibited materials. It will also be used to confirm the presence of prohibited materials in animal feed, replacing the 2006 PCR-based method.
Once it fully replaces both feed microscopy and the 2006 PCR-based method, the new 2009 real-time PCR-based method will increase the FDA's ability to detect prohibited mammalian protein in animal feed and prevent BSE in U.S. cattle. This strengthens the FDA's mission to protect animal and public health by keeping the food supply safe for both animals and people.