February 2015 for a set of 100 mammals (including cats, dogs and production animals) deemed appropriate as pets on the recommendations of Wageningen University. Parliamentary debates about such a pet list date back to the 1980s, with continuous disagreements about which species should be included and how the law should be enforced. In January 2017, the white list was expanded to 123 species, while the black list that had been set up was expanded (with animals like the brown bear and two great kangaroo species) to contain 153 species unfit for petting, such as the armadillo, the sloth, the European hare, and the wild boar. Killing and eating pets In January 2011, the Belgian Federal Agency for the Safety of the Food Chain stated that people are not allowed to kill random cats walking in their garden, but '[n]owhere in the law does it say that you can't eat your cat, dog, rabbit, fish or whatever. You just have to kill them in an animal-friendly way.' Since 1 July 2014, it is illegal in the Netherlands for owners to kill their own cats and dogs kept as pets. Parakeets, guinea pigs, hamsters and other animals may still be killed by their owners, but nonetheless when owners mistreat their companion animals (for example, in the process of killing them), the owners can still be prosecuted under Dutch law. Environmental impact Pets have a considerable environmental impact, especially in countries where they are common or held in high densities. For instance, the 163 million dogs and cats kept in the United States consume about 20% of the amount of dietary energy that humans do and an estimated 33% of the animal-derived energy. They produce about 30% ± 13%, by mass, as much feces as Americans, and through their diet, constitute about 25–30% of the environmental impacts from animal production in terms of the use of land, water, fossil fuel, phosphate, and biocides. Dog and cat animal product consumption is responsible for the release of up to 64 ± 16 million tons CO2-equivalent methane and nitrous oxide, two powerful greenhouse gasses. Americans are the largest pet owners in the world, but pet ownership in the US has considerable environmental costs. Types While many people have kept many different species of animals in captivity over the course of human history, only a relative few have been kept long enough to be considered domesticated. Other