Epidemiologists are investigating the possible link between the recent avian flu outbreaks in dairy cows and the use of poultry litter in animal feed. Poultry litter, which is a mixture of manure, feathers, and other materials, can contain disease-causing bacteria and viruses, including the highly pathogenic H5N1 strain of avian flu. Although the practice of feeding poultry litter to cattle is legal in many states, it raises concerns about the potential for disease transmission and the safety of the food supply. California has banned the feeding of poultry litter to lactating dairy cows, but it is still legal to sell it as feed for beef and other cattle. While the federal government does not regulate poultry litter in animal feed, some states have implemented their own regulations to address contamination and processing concerns.