Depletion of fenbendazole sulfone residues in northern bobwhite (<i>Colinus virginianus</i>) liver following medicated feed treatment

Northern bobwhite quail (Colinus virginianus) are an important game bird that generates substantial revenue for rural communities and is also an important grassland conservation species. Unfortunately, northern bobwhite populations have been declining across their range for more than 50 years. In the southwest bobwhite range, parasites are suspected to contribute substantially to the decline. To test the relationship of parasites and wild northern bobwhite populations, an anthelmintic medicated feed was developed. The medicated feed was then tested as part of the U.S. Food and Drug Administration registration process. Because northern bobwhite are a game species and harvested birds are ingested by people, it was necessary to estimate the tissue clearance rate of the drug. This study examined how quickly the conjugated metabolite fenbendazole (FBZ) sulphone was cleared from quail liver. A validated liquid chromatography-tandem mass spectrometry method was used to determine clearance rate from pen-reared northern bobwhite fed the anthelmintic at 110 ppm in feed. Results of the tissue clearance study found the drug never exceeded the maximum allowable concentration of 6 ppm and was cleared from the liver in 9.38 hrs. Based on the Center for Veterinary Medicine guidance for industry #3, a 0-day withdrawal period was assigned to the recently registered medicated feed in wild northern bobwhite. Thus, the anthelmintic FBZ was shown to be rapidly cleared from northern bobwhite and represents a viable option for treating wild populations for parasite infections, while treated game birds remain safe for human consumption.